Assessment of urban trees and shrubs using remote sensing technology: A case study on Ramna and Uttara
INTRODUCTION 1.1 Background Dhaka is one of the fastest growing urban areas in the world and largest city in Bangladesh. It has a population about 9 million within DCC area and over 10 million in the Dhaka Metropolitan area, which seems beyond its â€˜carrying capacityâ€™. Historically, the city is the hub of multifaceted activities including commercial, residential and industrial etc. Rapid and unplanned urbanization with poor population characterized it as a chaotic city. Landscape of the city is characterized by Pleistocene Madhupur tract and depression flood plain deposit whereas most of the built up areas were developed in Madhupur tract. Physiographic nature of the city is bounded by flat land tilted from north-west to south-east. It is also surrounded by four rivers such as Buriganga at the south, Tongi khal at the north, Turag at the west and Balu at the eastern side known as Metropolitan area. Urban Dhaka is rapidly growing and the mega city is facing various severe environmental problems like wetland loss, biodiversity loss, huge extraction of ground water, unplanned high rise building, discharge of industrial wastes in rivers and water bodies, pollution due to sound and gas emission, water quality degradation and over all vectors of many diseases find a heyday to create health problems
The increasing population exerting pressure on the land cover of greater Dhaka city by converting the lands to built up areas. Thus the landscapes are changing in the form of filling-up wetlands and water bodies together with destroying vegetation cover. These activities are happening mostly unplanned manner which leads the land cover to inundate extensively and to flood vulnerability.
Again, climate change signifies the impact of land use change. As land use change contributes to the global warming by increasing temperature and high rainfall anomaly creates the problem of flood vulnerability. Due to the destruction of vegetation cover and wet lands, the percentage of relative humidity and evaporation is showing undulation over the time period which creates problems to the health of urban population. For sustainable development of environmentally polluted and hazard prone mega city, an integrated urban planning is very important. The present study will try to seek those problems especially urban greening and its various prospects at Ramna and Uttara.
1.2. General Greening Activities in Dhaka city. The development of multifunctional urban green structures can be an important contributor to sustainable urban development in terms of improving the quality of life and environment for current urban populations (Konijnendijk et al., 2004). Once the present Dhaka city forest and green areas were managed by the Forest Department, but after the establishment of Dhaka City Corporation (formerly named Dhaka Municipality), it is the main responsible organization for greenery activates. Besides, the Rajdhani Unnayan Kartripakkha (RAJUK) had been emerged in 1987 through the ongoing crisis of planned and controlled development of Dhaka City which prime intension was to develop, improve, extend and manage the city and the peripheral areas through a process of proper development planning and development control. The jurisdiction of RAJUK includes the City of Dhaka and it's vicinity in the Districts of Dhaka, Narayanganj and Gazipur covering an area of 1528sq. kms. With DCC and RAJUK, a number of state bodies, autonomous bodies, private organizations, NGOs, different societies are involved with greening activities in and around Dhaka city. Of them, the key state and autonomous authorities are Department of Environment (DoE), Local Government and Engineering Department (LGED), Bangladesh Forest Department (BFD), Dhaka Urban Transport Project Authority (DUTP), and Dhaka Transport Coordination Board (DTCB), Department of Archeology, etc. Apart from these, some NGOs like ASHA, PROSIKA, different financial organization, donor agencies such as ADB, World Bank are also taking part in greening activities in Dhaka city. Some social organizations like Society of Arboriculture, Bangladesh National Nursery Consortium (NNC) are also contributing their efforts for promoting greening activities. The greening activities in Dhaka got impetus during the British regime. The British rulers took several attempts in earlier phase of the previous century to develop Dhaka as a beautiful capital city of Assam and East Bengal with adequate greenery. Most popular Ramna Park is a successful outcome of their endeavor. Some remarkable improvement was happened during the Pakistan regime. Street and avenue plantation, establishment
of gardens, large area allocation tree plantation were the major activities at that time. After the independence in 1971, greening activities have not got any importance rather than other wide variety of urban development projects including sanitation, drainage, housing, and infrastructure. The first Master Plan of Dhaka was prepared in 1959 by a British firm. The Plan covered roughly 830 sq. km (320 sq. miles) with a target population little over 1 (one) million assuming an average annual population growth rate of 1.75% in the city areas. The Plan in general, suggested a broad planning principle and zoned the urban area accordingly for various activities. Protect urban trees, rehabilitate what has been destroyed, and plan for enhancing green resources were some key policies in this plan but unfortunately, there were no mentionable development that happened under this plan due to lack of financial resources, government unwillingness for allocating money, coordination of the activities of different organization etc. Although, the Plan was prepared for a period of 20 years (1959-79) but it lasted almost double till the enforcement of new plan in 1995. In 1995, Dhaka Metropolitan Development Plan, 1995-2015 was prepared for overall development of the city and its surrounding. The plan addressed Dhaka's urban planning issues at three geographic levels: sub-regional, urban and suburbs. This plan, indeed, a mile stone, for city greening with the aim of creating green areas compatible and functional for urban design and meeting the basic needs and values of local communities. Another remarkable planning policy is the National Forest Policy, 1994, prepared by the Ministry of Forest, which included multipurpose objectives for afforestation, social forestry, protected area management, etc. through the coordinated efforts of the government and NGOs and active participation of the people in order to achieve self reliance in forest products and maintenance of ecological balance. A 20-year strategic visionary plan then dubbed the 'Dhaka Environment Programme' which has been devised by the DoE for the improvement of the city's environment including strategies and approaches to establish a 'Green Dhaka'.
Though some form of greening activities were carried out in different times, indeed, it has got priority very recently. DCC has taken initiatives for beautification and greening of Dhaka city by planting trees in existing parks including establish new parks, play grounds, constructing fountains and other installations at various intersections/ roads and maintenance of 67 road medians and islands for a four-year term. Beside, unpaved parts of roads and footpaths are used for the plantation of decorative plants and shrubs. The implementation of the project is running by the Beautification Cell of DCC involved with large number of banks, educational institutions, hospitals and business organizations. Dhaka Urban Transport Project (DUTP) and Dhaka Transport Coordination Board (DTCB) have also taken different actions to make the city roads beautiful and decorated, with the support from different organizations. Another activities are carrying out under the project named 'Good Governance and Development' by linking all Ministries, Departments and Agencies. Bangladesh National
Nursery Consortium (NNC) and Horticulture wings of Agriculture Ministry are continuously trying to promote nursery and gardening activities in the city. Prime Minister's Award for afforestation and Tree fair introduced in 1992 and 1994 respectively in nationwide for creating awareness and inspired the people for tree plantation. Again the Uttara residential area is recent development of RAJUK and City Corporation (North). The large green fields are now converted into residential though most of the place remained untouched.
1.3 Remote Sensing and GIS: Land use and Greening Remote Sensing and Geographic Information Systems have widely been used for land use mapping (Dewan et al. 2006). Remotely sensed data provides the instantaneous and synoptic view for land use and vegetation cover assessment. The typical spectral reflectance is useful to obtain correct information from the ground objects. Land use change can be analyzed with the help of Remote Sensing data. Extraction of land cover information can be done by using Land sat ETM and ASTER Images directly. The 15m ASTER image can provide more accurate data than 30m Land sat ETM image. It can be monitored and evaluated the rapid changes of land cover by using RS and GIS mutually. In contrast to the land use and flood hazard assessment, the 90m Shuttle Radar Topographic Mission (SRTM) data were further re-projected with Survey of Bangladesh (SOB) used projection in order to obtain the land elevation information of Dhaka using Remote Sensing extensively. 1.4 Underlying Principle Trees have been an important part of human settlements throughout history, only recently has their full value to urban dwellers been considered. Trees and green spaces play an important role in improving city living conditions and to save from environmental degradation. In the past, urban forestry in developed countries was considered almost exclusively on the basis of its aesthetic merits. Now, a closer look is being given to the environmental services and quantifiable economic benefits they provide. In most developing countries, like Bangladesh, government and international support for urban forestry has been limited The dramatic urban population increase in these countries, together with a corresponding growth in needs for food, fuel and shelter, calls for the design of strategies in which forestry will play a larger role in providing such commodities and in improving the urban living environment
Moreover, sufficient study and research are not undertaken to improve the Dhaka city plantation. This paper discusses on status of Dhaka city plantation and inquiry the possible solution for the development of roadside plantation. I think my study will be helpful regarding this.
2. OBJECTIVES OF THE STUDY The aim of this research is to explore some association of population and for that matter land use with vulnerable situation due to floods and environmental disasters. The following are the specific objectives of this study: 1. The determination of land covers change. 2. The delineation vegetation coverage. 3. The analysis of climate change due to vegetation and land cover change. 4. Inquire the possible solution for the development of avenue plantation.
3. STUDY AREA 3.1 Introduction The study area is the Metropolitan Dhaka city (Uttara and Ramna) having an area of approximately 306 km² (Islam 2005) is surrounded by a network of natural drainage system the Buriganga at the south, Tongi khal at the north, Turag at the west and Balu at the eastern side. The area is gradually sloping towards the east (14m to1 m elevation) and characterized by vast wetlands and agricultural area Figure 2.1.The focused study areas are Uttara and Ramna statistical thana. It is a low elevated area which has the maximum elevation of 14 m. It is extending through north and south-east and Spatial location is 23° 50'N 90°20'E and 23°40'N, 90°30'E respectively.
3.2 Land cover Situation in Dhaka City Geologically, Urban Dhaka is a flat land and is located mainly on an alluvial terrace of madhupur tract (most built up areas), younger and old natural levee deposit (western and southern part) and high floodplain and depression (eastern and northern part) deposit (The Daily Star 2011). It has a fascinating history of erosion and deposition, changes of sea level and in climate change. The exceptional uniformity of clay sediments of this area reveals that it frequently undergoes tidal or marine conditions. It is also slightly tilted to the southeast so that the western edge generally stands 3-6 meters above the adjoining flood plains and the southeastern part is low and has been invade upon old Brahmaputra sediments. The elevation ranges from 1 to 14m above Mean Sea Level (MSL) which is shown in Figure 3.2 by using Shuttle Radar Topographic Mission (SRTM)-90m resolution data which shows undulated topographic condition.
The soils are relatively mature. In profile, they consist of a thin brown loamy topsoil overlying a red, friable, clay loam to clay subsoil which at 0.7-1.5 meter grades into a strongly mottled friable to clay substratum with red, brown, drained, but acid in reaction and relatively low in plant nutrients . The study area also lies in the madhupur tract and younger and old natural levee deposit, which is characteristically different form each other. Figure 3.1: The Study Area denoting Dhaka Metropolitan Area (Uttara and Ramna) Hydrologically, the study area is situated in the terminal of the three major rivers - the Jamuna, the Padma, the Meghna and the old Brahmaputra flowing towards southeast (Sultana 2005). It is also closely dissected by a number of rivers and khals which are hydro-dynamically connected to the major rivers. The rivers carry the highest amount of rainfall during the monsoon season which is 90 % of the mean annual rainfall (Huq and Alam 2010). They discharge highest amount of water during the monsoon and reached to the highest level during this season (June-October). The incised drainage system is well developed and floodplains consist of back swamps, depressions and meander lakes which are comparatively ill drained. The hydro-dynamically mighty rivers and stream-streamlets are strongly interconnected. The Buriganga branching off from Dhaleswari and flows towards south east. The Turag river comes from the north and joins the Buriganga near Mirpur. The Balu river also comes from the north running through the eastern side and joins the Lakhya river near Demra. The Tongi khal takes water from the Turag river and discharge it into the Balu river. The Turag, Balu and Tongi khal all are perennial (Sultana 2005). These rivers shrink during dry season and turn into overloaded during rainy season. Climatologically, it is characterized by hot and humid subtropical climatic conditions demarked with short and cool winter and hot summer with high rain fall. It is situated at the Southcentral climatic zone (Banglapedia 2008) with highly variations of temperature, humidity and evaporation etc. The mean annual rainfall is 2147 mm and average relative humidity (70-75%) with 1150mm of evaporation (BMO 2011). The temperature is highly variable than surrounding rural areas. The city is characterized by increasing trends of population (Figure 2.2) and high density. It is the fourth largest mega city
(UNFPA 2009). Average density of population is 7918.43 per kmÂ˛. The annual growth rate is 4.5 % (Islam 2005) showing the increasing trends over the year.
Figure 3.2: Digital Elevation Model (DEM) of Dhaka Metropolitan Area (DMA) by using Shuttle Radar Topographic Mission (SRTM) data.
Figure 3.3: The population growth of Dhaka Metropolitan Area (Source: BBS 2001, 2008; BARC 2004 and BCAS 2005, Islam 2005, UNDP 2010). 3.3 General Landuse Scenario General land use of the city comprised of commercial and industrial activities mostly occurring in unplanned manner. The land comprising of residential, industrial and commercial are about 33.45% of 208km² and percentage of vacant land is about 3.09 (BCAS 2005). The physical growth of the city mostly directed to the north-east. Rapid and unplanned urbanization, commercial development and with population pressure have made this city worst in terms of living perspective.
4. REVIEW OF LITERATURE 4.1. Urban forestry concept Urban forestry is not a new concept, but it is one which appears to have growing potential. This is particularly true in developing countries, where urbanization is increasing at a rapid rate and a demographic switch from a predominantly rural to a predominantly urban society is taking place. Although United Nations (UN) (1991) figures indicate that in 1990 only 37% of the total population of developing countries was urbanized, it is predicted that by the year 2025 the proportion will be 61%. Already rapid and uncontrolled urbanization in many developing countries is having fundamental social and environmental consequences. The role of urban trees in ameliorating this situation might, at first thought, appear to be small. 4.2. Definition of the term ‘urban’ Urban areas in developing and developed countries are often very different. Furthermore, although we know intuitively what is ‘urban’ and what is ‘rural’, there is actually no universally accepted criterion for distinguishing between such settlements. The usual mechanism, common in national censuses, is to take population thresholds. Once a nucleated settlement grows beyond a certain threshold, it becomes ‘urban’. However, the threshold used varies widely from country to country, and may even change in successive censuses (Hardoy and Satterthwaite 1986). The United Nations has attempted to standardize data by defining settlements of over 20,000 people as ‘urban’, over 100,000 as ‘cities’, and over 5 million as ‘big cities’. In contrast, Hardoy and Satterthwaite define any nucleated
settlement of more than 5,000 as an urban centre, those having a population of less than 20,000 being ‘small urban centres’, and those having some 20,000 to 100,000 inhabitants being ‘intermediate urban centres’. Whatever the figure used, generalizations are inevitably unsatisfactory. A small Pacific island whose total population is under 20,000 will obviously have a different perspective on urban settlements from a large, heavily populated country such as India. Different national perspectives may well reflect historical, cultural and political differences. This varied concept of an ‘urban settlement’ should be remembered throughout the ensuing discussion. It is also worth noting that the ‘cut off point’ on the ground for an urban centre is interpreted differently in different countries. An obvious example of this is in China, where cities often ‘annex’ a number of adjacent districts into their administrative areas in order to ensure control over the supply of essential urban services, such as reservoirs or power plants. The official population of many Chinese cities thus includes many rural dwellers (Drakakis-Smith 1987). 4.3. Definitions of urban forestry The definition of urban forestry given by Miller (1988) is of, “An integrated, city wide approach to the planting, care and management of trees in the city to secure multiple environmental and social benefits for urban dwellers.” The definition of urban forestry given by Grey and Deneke (1986) is of, “Urban forestry is the management of trees for their contribution to the physiological, sociological, and economic well-being of urban society. Urban forestry deals with woodlands, groups of trees, and individual trees, where people live - it is multifaceted, for urban areas include a great variety of habitats (streets, parks, derelict corners, etc) where trees bestow a great variety of benefits and problems.” 4.4. Concept of Peri-urban forestry Peri-urban forestry is loosely defined as forestry on the fringe of urban settlements, but given the lack of conformity between countries as to what constitutes ‘urban’, a precise definition of ‘peri-urban’ is unfeasible. To use the simple definition of the area used by urban residents is inadequate, since this may extend far into rural areas; as theories such as that of Von Thunen have shown the sphere of influence of a city or town may be very wide. To define peri-urban solely in spatial terms is also unsatisfactory, since it can be so variable. Many urban foresters are unwilling to accept peri-urban forestry as a separate concept; they argue that the peri-urban area, or urban fringe, is simply one location for urban forestry. This argument has been accepted in the compilation of this document, so that all further mention
of urban forestry may be assumed to include peri-urban locations, unless otherwise indicated. (Carter 1993). 4.5. A new approach to the potential of urban forestry in developing countries The potential of forestry in and around urban settlements may be approached from one of two broad perspectives. One is to focus upon the trees themselves; the potential benefits and problems that may be expected from their cultivation in an urban environment; how they may be managed to maximize the former; and what threats an urban environment pose to their survival. An alternative perspective, which this paper attempts, is to focus first on the residents of urban areas, their needs and the nature of their invariably diverse living conditions, and then to consider how trees might be of benefit to them To learn more about the urban dweller, especially in the developing world, it is necessary to consult geographical or other social science texts. These rarely devote much attention to peoples' use of and perceptions of trees, except, to a certain extent, in the case of fuel wood supplies from periurban areas (Carter 1993). 4.6. History of urban forestry The planting of trees in human settlements and as an integral part of landscape architecture is not new; it has its roots in ancient Chinese, western Asian and Greek civilizations (Jellicoe 1985). A number of ancient cities had highly developed parks, gardens and other green spaces - the most notable being Babylon, "the mother city of gardens'', dating back more than 3000 years. The Assyrian civilization and, much later, the classical Persian and Greek civilizations arising in the fifth century BC, also had such a tradition, based on amenity as well as cultural and religious beliefs In Europe in the seventeenth and eighteenth centuries, municipal and crown forests were managed for recreational hunting. Later, the elite developed urban gardens and parks as visual amenities in many European cities, particularly Italy, France, Austria and England. The practice of urban amenity plantings subsequently spread to colonies in Africa and Asia. Spanish colonization introduced into Latin America the concepts of interior patios in houses and public plazas in urban centre. Just as the rate and extent of urbanization vary considerably in the Third World, the nature and character of urban settlements also vary according to the individual culture, politics and past of different countries. This is reflected in urban forestry practices, with some countries having a long history of urban tree cultivation. For example, it is known from the writings of Marco Polo that extensive roadside tree plantings were a feature of 13th century China (Pollard 1977). In Mexico City, the forest of Chapultepec was first established by the
Aztecs as temple gardens (Benavides Menza 1992), while in India a number of urban parks were established by sultans and maharajas (an example being the Lal Bagh park in Bangalore -Sunder 1985). Many countries of the Third World share a history of colonialism which exerted a profound effect on the process of urbanization. They are an early mercantile period (beginning in the 1500s or later), a period of industrial colonialism (the 1850s onwards), followed by late colonialism (1920s onwards) and then independence (late 1940s to 1960s). The dates are given as an indication, and pertain most closely to Asia. Outside influence during the mercantile period was mainly confined to existing urban settlements, particularly ports, where residential areas tended to be already segregated along ethnic or occupational lines. During the industrial period, colonial control was exerted at all levels of the urban hierarchy, and a tendency towards urban primacy emerged (one â€œprimateâ€? city dominating all others). Often laborers from outside the local area were imported to work in assembly or production. Social, economic and spatial separation was generally reinforced, so that different areas of a city took on a particular character. According to Onganga (1992) in the minds of many local Kenyans, at least, this has left urban amenity trees negatively associated with the colonial past. In some countries, continuing contacts with former colonial powers, then short of labour, resulted in a flow of workers to Europe during the 1960s. This, however, was short lived; by the end of the 1960s, the world economic system began to change radically, and labour in the North was becoming more organized and expensive. Many European and North American companies began to relocate in Third World cities, where labour was cheaper. It is this phenomenon, the New International Division of Labour, which has had the most sweeping effect upon the nature of Third World cities today. For the purposes of the present discussion, a number of key points may be noted. The vegetation of Prague has been influenced by agriculture since neolithic times. Historical records from the thirteenth century describe a wood shortage which led King Jan to establish a wood marketplace near the city. In 1350, King Charles IV ordered the preparation of strict regulations controlling the use of forest lands. In 1740, King Charles VI ordered the planting of trees along roadsides; nobles owning land abutting on roads were to care for and profit from the trees. In 1752, Empress Maria Theresa broadened the decree to include the planting of trees on all new roads in order to orient
travelers in fog and snow, increase wood production and enhance the appearance of the landscape. The first major reforestation of Prague was undertaken in 1854 and, between 1897 and 1908; substantial efforts were made by public beautification commissions to revegetate open spaces and eroded hillsides throughout the city (Valesova 1985).
4.7. Purpose Urban forestry The need for urban forestry to be a planned, integrated, and systematic approach to urban tree management should be stressed. Planning is important because trees are very often considered as an afterthought once development has taken place, rather than being incorporated at the original design phase. An integrated approach implies the participation of many different organizations - local councils, municipal and national planning bodies, departments, etc. Systematic management entails regulated tree management; operations such as planting, pruning, and felling must all be conducted in an organized manner, at the appropriate time. In industrialized countries urban forestry is concerned primarily with environmental enhancement. Even in countries (e.g. Germany), where timber is harvested from peri-urban forests, the major management objective is providing recreation/education of the urban dweller, and timber harvesting operations are significantly modified accordingly (Carter 1993). Urban forestry plays a vital role in the following ways---4.7.1. Improving the aesthetic quality of urban areas It is the aesthetic and recreational value of trees, forests and parks that is most directly identified by most urban dwellers, in developed and developing countries alike. Trees fulfill certain psychological, social and cultural needs of the urban dweller (Dwyer Schroeder and Gobster 1991). They play a very important social role in easing tensions and improving psychological health; people simply feel better living around trees. Parks provide easily accessible recreational opportunities for people. 4.7.2. Ecological maintenance As a result of the predominance of concrete buildings, asphalt and metal as well as the concentration of transport systems and industrial activities in and around urban areas, the median temperature is higher (the "heat island" effect), the air is drier and often polluted,
rainfall is less efficiently absorbed and the environment is generally noisier than in a rural setting (Kuchelmeister and Braatz 1991). 4.7.3. Cleaning the air One of the major problems in urban areas is poor air quality. Plants help remove pollutants from the air in three ways: absorption by the leaves or the soil surface; deposition of particulates and aerosols on leaf surfaces; and fallout of particulates on the leeward (downwind) side of the vegetation because of the slowing of air movement. Research on the removal of airborne pollutants by vegetation shows that plants are effective sinks for pollution. Trees absorb sulphur dioxide very efficiently. Keller (1979) has quantified an 85 percent reduction in lead behind a shelter-belt of trees. Soil effectively absorbs gaseous pollutants, including carbon monoxide, sulphur dioxide, nitrogen oxides, ozone and hydrocarbons. Trees intercept dust: a belt of trees measuring 30 meters in width has been found to intercept almost all dust in the air. 4.7.4. Modifying temperature extremes Trees, shrubs and other vegetation help to control temperature extremes in urban environments by modifying solar radiation. The shade of one large tree may reduce the temperature of a given building to the same extent as would 15 air conditioners at 4000 British thermal units (BTU), i.e. 4220 kJ, in a similar but unshaded building. Energy saving through tree-planting around houses ranges from 10 to 50 percent for cooling and from 4 to 22 percent for heating (NAA/ISA 1991). 4.7.5. Noise reduction Noise is often referred to as invisible pollution. Excessive noise levels in most major cities contribute to both physical and psychological damage. Trees can help both by absorbing and refracting or dissipating noise such as that produced by the heavy vehicular traffic which characterizes urban areas (Kuchelmeister and Braatz 1991). 4.7.6 Meeting resource-poor people's basic needs Beyond their aesthetic and ecological value, trees can contribute to the satisfaction of energy requirements as well as the daily food requirements of urban dwellers, particularly in the case of the poorest elements of society (Kuchelmeister and Braatz 1991).
4.7.7. Urban forestry provides Fuel wood Although "high technology" sources of domestic and industrial energy are available in most cities (electricity and petroleum products such as diesel, kerosene, gas), their relatively high price puts them out of the reach of much of the urban population in the developing world. Therefore, people continue to depend on fuelwood and charcoal for their energy needs which are consequently satisfied by uncontrolled collection, often resulting in the extensive degradation of areas around many urban settlements in developing countries. When "free" wood energy supplies are exhausted or are too difficult for people to tap into, fuelwood markets develop. Even this energy source is relatively expensive; studies report expenditures of 30 to 40 percent of total income by low-income groups to meet domestic energy requirements. Wood-based building materials - poles, branches and leaves for thatching, for example - are also in high demand in many urban areas (Kuchelmeister 1991; Ducchart 1989).
4.7.8. Food production Urban agriculture is common in many cities in Asia, Latin America and Africa (Yeung 1987; Sanyal 1985; Streiffeler 1987; Ninez 1985; Skinner 1981). Who and how many people practice it as well as what form it takes differ greatly from place to place. It is most often practiced in the urban fringe area by low-income families but, in places such as Africa and the Pacific Islands, urban agriculture is widespread within cities. Although in most places the emphasis is not on the production of staple foods, through the production of vegetables, fruits and condiments, urban agriculture can contribute to the improvement of the nutritional value and variety of city dwellers' diets. 4.7.9. Environmental benefits Environmental benefits to be gained from urban trees in the developing world include landscape enhancement, recreation, education, and general well-being; a habitat for wildlife; climatic modification; the control of air and noise pollution; erosion control; the protection of catchments areas for urban water supplies; and the productive use or safe disposal of urban wastes. (Carter 1993) 4.8. Potential problems from urban forestry
A number of the potential problems of trees in urban areas are discussed with regard to species selection. However, a brief review is of use here, both of the problems and possible means of avoiding them. 4.8.1. Cost Urban forestry initiatives conducted on a scale beyond small home gardens can cost a large amount of money to implement. This is particularly the case if instant results are wanted in amenity plantings, so large saplings are planted which require intensive after care in the first year or so of establishment. Maintenance costs, in particular irrigation, can be very high in such situations. Poorly run tree planting campaigns can also prove to be very costly, if mortalities are high as a result of inadequate or misdirected support. There are numerous ways in which costs can be minimized and benefits maximized through appropriate technology and careful planning but arrangement for regular maintenance is crucial. (Carter 1993) 4.8.2. Threats to human safety Poorly planted or inappropriate tree species can serve as a hazard to urban inhabitants, either directly (through falling branches or the falling over of the entire tree) or indirectly. The former may be particularly likely in countries where typhoons or hurricanes are regularly experienced. It is possible that they are also of increasing occurrence in former colonies where colonial tree plantings are now over-mature and in need of replacement. Whereas in many developed countries there is provision for ensuring the removal or treatment of dangerous trees, this may not exist, or fail to be implemented in some developing countries. The general result is that there is probably more cause for genuine concern about the safety of trees in cities of developing rather than developed countries. Onganga (1992) comments that in Kenya, for example, problems with â€œtrees blocking highways and falling on roofs of houses are common in urban areas.â€? Careful planting and choice of species, regular maintenance and a clear line of responsibility for dealing with dangerous trees would help to increase human safety. 4.8.3. Structural damage The roots of street trees often cause the cracking of roads and pavements and sometimes water pipes. Urban trees can also cause structural damage to buildings, both at foundation level due to their roots, and through the falling of whole trees or branches. As with
human safety, such problems can be minimized by careful species choice and maintenance (Biddle 1987). 4.8.4. Vandalism and browsing Damage may be inflicted on trees simply out of intent to destroy; out of casual disregard; as a consequence of harvesting tree products; and by browsing livestock. While many foresters and arboriculturalists would classify all these as vandalism, there are clear differences. Only deliberate and casual vandalism are generally a problem in the developed world, whereas all four occur in Third World cities. Apart from any other considerations, this probably renders them a more difficult environment in which to raise trees (Sunder 1985). The most important issue in combating all forms of human and animal-induced tree damage is gaining local people's support for and active involvement in tree cultivation. Apart from this, urban amenity plantings can be planned to minimize the likelihood of vandalism. Trees planted within cultivated ground tend to be less susceptible to deliberate or casual damage than ones surrounded by tarmac or concrete, as are ones planted in groups compared with lone trees. This is substantiated by observations of street trees in Bangalore, India. Here it was noted that, the position of tree stakes can also influence vandalism; trees with stakes that reach to breast height are more likely to be snapped off at this point than ones which have lower, less obvious stakes (Sunder 1985). 4.8.5. Access to solar energy In developing as well as developed countries which receive significant solar radiation, solar power is an increasingly utilized energy source. While trees may be valued for their cooling shade, if this reduces solar radiation falling onto a solar panel, it may be viewed as a nuisance. In many States of the USA, there are now laws regarding access to solar energy which effectively require trees blocking solar radiation to be pruned or removed (Miller 1988). Although such legal difficulties are unlikely to affect urban tree growers in developing countries, the issue of access to solar energy is one which may be of increasing future importance. The extent of mutilation is clearly inversely proportional to the extent of tree cover in a locality. The fewer the trees, the more insidious the process of destruction, we have either very little, or almost total mutilation in any locality it seems as if there is a psychological threshold involved: once people get over the inhibitions and into the habit of hacking trees,
they go and hack every one of them(Gadgil and Parthasarathy 1977).It is common in Kenya, during funerals of important people or when a home team wins a prestigious cup, for people to cut trees and carry branches as a sign of sorrow or victory. One day's riot can leave an entire park stripped of thousands of trees (Onganga 1992).
4.8.6. Unorganized waste disposal Rather than being a means of recycling urban waste, urban forests may be used as dumping grounds in manner that is wholly deleterious to the environment. Urban forests are considered by many people as the most ideal place to dump industrial waste. This is a major problem which is not easy to solve in Kenya because it involves very rich and influential people. Waste from tires, bottles, and other industrial by-products quite often covers several acres that otherwise could be used for tree planting. These waste products have also become a health hazard to the urban dwellers (Onganga 1992). 4.9. Changes in Urban Forests through Time The structure of the urban forest changes through time in response to a wide range of powerful forces. These changes originate from diverse human and natural actions operating directly and indirectly on the urban forest and its management. The impacts of these forces for change vary over time and across and among urban systems; they contribute to different urban ecosystems and rates of change across urban areas. By understanding how human and natural forces interact within urban systems to create change, management can minimize negative forest changes and facilitate positive changes (Dwyer Nowak Noble and Sisinni 2000). Human forces for change in urban forests include: •
Urban resident involvement in tree planting, maintenance, and management
Plant community and species preferences or fads
Influx of funds to plant trees and other vegetation
Management of urban infrastructure
Urban development and land use change
Development of new urban forest management techniques and tools
Increased interest in quality of the urban environment and urban life
Changing character of the urban population (race, ethnicity, and age structure)
Byproducts of urbanization (for example, air and water pollution)
Natural forces that can lead to changes in urban forest structure include: •
Extreme precipitation or temperature events
Storms and other natural disasters
Aging of the existing forest
Insect and disease outbreaks
(Dwyer Nowak Noble and Sisinni 2000) What most distinguishes the urban forest from exurban forests is the dynamic influence of people. Human activities not only change urban forest structure to meet design and functional needs but also try to minimize and prevent detrimental changes due to natural forces (for example, controlling insects and diseases or altering structure to reduce the risk of wildfires) to sustain desired forest structure. A combination of human actions and natural forces will continue to shape the urban forests in the years ahead. These interacting forces highlight the need to coordinate urban forest resource management with many other urban activities (for example, land use planning, environmental protection, residential development, infrastructure development and maintenance, community empowerment and revitalization, and environmental education). Management of these complex, dynamic systems requires involvement of many disciplines, organizations, owners, users, and managers to sustain ecosystem health and desired functions. A principal goal of urban forestry is to sustain forest structure, health, and benefits throughout the urban ecosystem over the long term. Comprehensive and adaptive management approaches are needed to do this. Expanding the management focus of urban forests to all trees, associated resources, and their benefits across the urban ecosystem will require nontraditional urban forest management techniques. The overall societal benefits of implementing such management are likely to be substantial (Dwyer Nowak Noble and Sisinni 2000). Management also must be comprehensive in terms of its process, and it must be adaptive to allow for adjustments in management activities based on new situations and information. To attain comprehensive and adaptive management, urban forest managers should consider: •
The desires and needs of the community
What urban forest structure is necessary to best address community needs?
Periodically reassessing community needs and urban forest structure to ensure
that management plans remain appropriate To facilitate comprehensive and adaptive management to sustain the entire urban forest ecosystem, the following topic areas need to be emphasized: •
Improving inventory and assessment
Improving dialogue among owners, managers, and users
Fostering collaboration among agencies and groups
(Dwyer Nowak Noble and Sisinni 2000) 4.10. Opportunities for Improving Urban Forest Resource Management •
Improving the understanding of how forest configurations influence forest use
and benefits •
Increasing knowledge about factors that influence urban forest health
Improving the dissemination of information about urban forests and their
management With improvements in the above areas, urban forest resources can become a more highly valued component of large-scale and long-term environmental and community planning. Facilitating the effective management of urban forest ecosystems in the United States requires forging partnerships and collaborative efforts across resources, disciplines, organizations, and geographic areas. One continuing issue is to understand the relation between the management of urban and exurban resources, such that collaborative management efforts across these areas can be fostered. This assessment is the first step in developing a comprehensive understanding of the national urban forest resource and can assist in development of comprehensive adaptive management plans in both urban and exurban environments. As an increasingly urban population continues to play a key role in the social and political structure, understanding and managing of urban forest resources will be a critical mechanism for improving forest benefits and connecting people with ecosystems in the 21st century (Dwyer Nowak Noble and Sisinni 2000). 4.11. Urban Forestry Round the World Most of the country practices urban forestry around the world. We discuss here into two ways- outside Asia and within Asia. 4.11.1. Urban forestry in the United States
The beginnings although the term did not come into common usage until the 1960s, urban forestry has been around as long as people have been planting trees in towns and villages where they live. In North America, early settlers cut the virgin timber to clear building sites and farm fields, construct their buildings and heat their houses, but it was not really until the late 1700s and early 1800s that Americans began to plant trees in towns and villages. In fact, Philadelphia, a historic city in Pennsylvania, did not have street trees until the late 1700s, partly because insurance companies would not insure houses with trees in front of them (Zube 1973). Community groups of all kinds participated in the planning and development of these forests, including schools, local governments and churches. Their activity marks the beginning of the American people's involvement with their forest resources. By 1953 a census of community forests recorded a total of 1752815 ha (Duthie 1953). Today, few people who benefit from these forests realize their size or value. One common problem for the urban forests of American cities is the creeping crisis that sets in as city trees grow and mature while budgets and programmes shrink. In 1984, the delegates at the national meeting of the directors of parks and recreation identified trees as their biggest maintenance problem, a problem they have yet to communicate effectively to the public or their political leaders (Moll and Gangloff 1886). 4.11.2. Green space in metropolitan Prague today Today, fully 10 percent of metropolitan Prague is covered with forest vegetation. There are marked differences among the tree compositions of streets, parks, private yards and courtyards. Vegetation structure is influenced by several factors but the age and structure of buildings appear to have had the greatest influence. The density and type of tree tends to reflect the management choices and species preferences at the time of neighborhood establishment. In Stare Mesto (the old town), which retains a medieval character, vegetation is almost absent, but in sections of another old zone, Mala Strana (the lesser side), where palace gardens are common, green space may be as high as 20 percent of total land area (Profous and Rowntree1990 ). The densely constructed apartment blocks which were common at the turn of the century also have very little green space, while newly constructed residential areas may have as much as 60 percent, largely because of the presence of undeveloped city blocks (Jelen 1985). 4.11.3. Urban forestry in Debre Birhan, Ethiopia
Debre Birhan is situated on the high plateau 140 km north of Addis Ababa. In Ethiopia, over 90 percent of all energy consumed is for domestic needs, and fuelwood supplies 40 percent of the total. The rest comes from animal dung, crop residues and kerosene. The consequences of this rapid deforestation are severe, especially for urban centres, fuelwood when it is available at all, can cost as much or more than kerosene. A recent effort to meet the problem of urban fuelwood supply is the FAO Debre Birhan fuelwood Plantations Project, started in 1986. Financed by a US$2555690 grant from the Danish international Development Agency, the project's major goal is to increase the fuelwood supply on a long-term basis. It also aims to strengthen Ethiopia's capacity to plan and manage similar projects in some 50 urban areas already identified as facing critically low supplies of wood. Studies indicated that an adequate, sustainable fuelwood supply for the city would require at least 3200 ha of plantations, mostly of fast-growing eucalyptus. However, such plantations would require 25 percent of all land in the area, land now used for crops and grazing. Since a sudden change in land use on this scale would have drastic economic and social consequences, only 1100 ha have been scheduled for planting over the next three years (Haque 2003). 4.11.4. Urban forestry in Tashkent, USSR Tashkent, lying at the western end of the Tien-Shan mountain range in Soviet Central Asia, is the capital of Uzbekistan and the site of a large textile industry. The present centre's open plan combines decorative modern buildings with attractive landscaped areas. Tree canopies shade many of the streets from the intense summer sun. The most common street species by far is the western variety of maple (Acer negundo var. californicum), with its bold and very hairy foliage. Other frequently seen North American species are white ash, honey locust and Osage orange. English oak, with its luxuriant foliage, provides excellent shade (Haque 2003). 4.11.5. Urban forestry in Colima, Mexico In Colima, Mexico citizen groups at times can play a decisive role both in heightening public awareness of the value of trees in the urban environment and teaching people how to care for them. One example is the recent work of the Pro-Ecologia de Colima, a nongovernmental organization based in Colima, a town near the Pacific Coast directly west of
Mexico City. To encourage citizens to take the initiative in planting and tending trees, the guide gives illustrated instructions as to where and when to plant trees, how to prepare the soil, how to plant to ensure maximum chances of survival and the care needed for good growth (Haque 2003) 4.11.6. Milton Keynes, UK - Trees as investment In Milton Keynes, however, urban forestry is seen not just as a social investment but as a commercial one as well. Established and financed by the national government, Milton Keynes is intended to be one of several model communities which will repay the initial investment by enhancing rental income from housing and industrial sites. In Milton Keynes, these woodlands include: three natural "parks", the largest of which is 40 ha and the smallest 20 ha: 1200 ha of "linear parksâ€? or major green belts which run across the city; and some 22 small spinney and coppices. All of these have been developed from existing tree stands augmented by selected planting of exotics and regeneration planting of native oak, ash, field maple, cherry and hazel. All street and park planting and maintenance are carried out by the Landscape and Forestry Division of the town's Recreation Unit (Haque 2003).
4.11.7. Urban forestry in Canberra, Australia In Canberra the Australian government has kept to its original vision by passing legislation consistent with that purpose and has overtly encouraged the Imaginative use of the existing natural environment. Urban development has been allowed chiefly in the valleys, preserving the naturally forested hills and ridges which screen it off from most vantage points. River corridors are maintained as green space. In 1975, the concept of "essential landscape foreground areas" was introduced. Half a dozen of these landscapes, examples of typical Australian countryside, have been established along major highways on the south and western urban fringes where they provide a foreground to the seasonally snowcapped mountains in the distance (Haque 2003). 4.11.8. Urban forestry in Windsor, Ontario, Canada The city of Windsor, just across the river border from Detroit, Michigan, incorporates seven smaller communities interspersed with the remnants of market gardens and abandoned farmlands. Before the municipality hired its first urban forester in 1970, the area's tree cover,
predominantly elm and maple, was poorly managed and vulnerable to disease and insect attack. Now, however, Windsor has a carefully planned, well-managed urban forestry system with 600 ha of municipal parks and a closed canopy of mature trees along 1000 km of streets. Trees occupy almost 20 percent of the total space. In Windsor, Ontario tree planting has been a major activity. Since 1968 over 20000 street trees alone have been established. Most municipalities in Ontario use the common "bareroot" planting of trees 2 or 3 m in height. Although this method allows a large number of street trees to be introduced inexpensively, Windsor found that poor establishment and vandalism caused an estimated 30 percent loss (Haque 2003). 4.11.9. Kampala, Uganda - Fuel wood and ornamentals Urban forest management in Kampala, the capital of Uganda, focuses primarily on the expansion and maintenance of fuel wood plantations to meet the increasing demand for firewood and charcoal as the urban population grows and imported kerosene becomes more expensive. An important but secondary activity is the establishment of ornamental trees. As fuel wood purposes eucalyptus introduced from Australia and New Zealand, although the slower-growing Cassia siamea Lam is also used and as ornamental value include mango, papaya, avocado, guava and cashew nut used. Over a hundred species of ornamentals are being used, including several kinds of cypress and pine, Grevillea robusta, Callistemon citrinus (bottle brush tree), Sterculia acerifolia (flame tree), jacaranda, Delonix regia (flamboyant tree) and Araucaria (Haque 2003).
4.11.10. Urban forestry in Dunedin, New Zealand Few cities in New Zealand have large forest tracts within or close to their boundaries, and those that do have generally left them unmanaged. A notable exception is Dunedin, on the southeast coast of South Island. Dunedin has over 8300 ha of forest preserve inside the city limits. One tract of 200 ha is unique in that it almost encircles the city only 1 km from the centre. Forest management has been so successful from both an environmental and a financial point of view that the city council recently decided to increase the forest area to 12000 ha (Haque 2003). 4.11.11. Urban forestry in Beijing, People's Republic of China
Driving the 25 km from the airport to the city of Beijing, one is immediately struck by the trees - pines, willows and poplars three or more rows deep - which completely shade the entire route. Once in the city, trees continue to strike the eye, for they line virtually every street, flourish in every residential area, surround most public buildings and fill the many public gardens and parks. In modern China, tree planting is everyone's business. The national goal of "Five Ones" includes, as one of its "Ones", one hundred trees planted by each person. The national slogan of "Four Around Plantation" calls upon people to plant trees around houses (1), villages (2), along roads (3), rivers and canals (4) for production, protection and aesthetics. Urban forestry is taught in schools as part of labour education and the national health movement. However, responsibility for urban forestry is decentralized, and trees in Beijing and other urban centreâ€™s are maintained by the people, not "tree experts"(Haque 2003). 4.11.12. Hong Kong - Maximizing the use of space When the British first came to Hong Kong, they described it as a "barren" island with practically no trees. While the largest forest in a sense is now the city itself - a forest of concrete, glass and steel - almost 40 percent of the land area is "green space". And over onehalf of all existing stands of trees and shrubs were planted in recent years. The concern for urban forestry in Hong Kong is not new. A botanical garden was opened in 1864, and a decade later the forestation of Victoria Peak began. Before the 1950s, however, the city's only outdoor recreational facilities were one major park and a collection of private clubs. After the Second World War, a plan was commissioned which proposed the creation of 30 ha of green recreational space for every 100000 inhabitants. The proposal remained more or less on the drawing board until 1968, when a new recommendation halved that goal to 15 ha of green space per 100000 people in the city and 20 ha for towns in the New Territories. These targets have very nearly been met (Haque 2003).
4.11.13. Urban forestry in Yokohama, Japan Overlooking Tokyo Bay south of the capital, Yokohama has been an international port since Commodore Perry "opened" Japan to the West some 130 years ago. Yokohama has 1209 parks covering almost 600 ha, with an additional 4500 ha of suburban woodlands. This greenery, one of the striking features of Yokohama's river-fed delta plain and the surrounding
hills, has been the result of conscious policy, careful planning and hard work. For years the municipal government has been buying land in the suburbs in order to preserve it as "greenery conservation districts" or "citizens' forests". In 1980, a master plan for greenery activities was drawn up and incorporated into the "21st Century Plan for Yokohama", a comprehensive scheme to ensure an attractive and comfortable urban environment for present and future inhabitants. The plan calls for the protection and expansion of green zones in the city outskirts, the management of urban parks, the development of urban agriculture and forestry, and special protection of over 1000 individual famous trees, it also sets a target of 10 million planted trees by the year 2000, three times the present number (Haque 2003). 4.11.14. Singapore, Republic of Singapore - Aerating a concrete jungle The early 1960s saw Singapore's population mushroom; they also brought a firm commitment to make this world trade and tourist centre a garden city, a green metropolis. Since there were then relatively few trees within the city proper, the Singapore Parks and Recreation Department had to undertake a massive effort to achieve this goal. Two keys to its success are its massive "aeration" and "screening" programmes. Plants and trees in urban environments, where there is an abundance of concrete and asphalt surface, suffer from a poor distribution of rain-water and an inadequate air supply to their root systems. The "aeration programme" is designed to alleviate these problems. Present tree plantation not only provides growing space for trees and shrubs but also minimize the disturbance to root systems during the laying or repairing of cables, water mains and sewers. Car parks, both old and new, are planted with trees to reduce asphalt surfaces and many have been paved with perforated slabs to allow better air flow and water drainage (Haque 2003). 4.12. Characteristic of the urban forestry 4.12.1. Diversity Diversity is one of the most distinctive attributes of the urban forest. This feature is primarily a function of the many components of the urban forest, including trees and ground covers, soil types, microclimates, wildlife, people, buildings, infrastructure, and other developments. These elements are found in almost unlimited combinations in an intricate mosaic across the urban landscape. The elaborate mixture of natural and human-made resources in complex urban ecosystems broadens the scope of urban forestry beyond traditional forestry, arboriculture, and other natural resource disciplines. The diversity of urban forests is also a function of variations in land uses, land ownerships, residents and
visitors, and management objectives across and between urban systems. Urban areas are characterized by multiple land uses and diverse populations; consequently, the management of activities by different individuals and groups creates a complex landscape pattern reflecting an area’s unique combinations of physical, biological, and social attributes. With the diversity of land uses and owners in urban areas, the objectives and issues facing managers of the urban forest are wide ranging, extending from wildlife management to the mitigation of air pollution, enhancing aesthetic value, and providing recreation, flood control, fire prevention, and other benefits. Several factors serve as catalysts for increased diversity in urban forest ecosystems. Shifts in population, changes in economic activity, improvements in transportation, and other developments increase the range of land uses, broaden the spectrum of people involved, and complicate the mixture of old and new, artificial and natural, and native and exotic natural resources in urban areas (Dwyer Nowak Noble and Sisinni 2000). 4.12.2. Connectedness Connectedness among resource components, and with other resources, activities, and functions within and beyond the urban environment, is another key attribute of the urban forest. Other elements of urban environments include roads, homes, industrial parks, and downtown centers. Whether connected by the logistics of managing urban infrastructure (for example, coordinating maintenance of urban trees and power lines, sewers, sidewalks, and roads), or by contributing to the overall character of the area, urban forests link “landscape” with “architecture” and become an important component of urban planning. The connectedness of urban forests is reflected in their contribution to a wide range of urban issues, programs, and initiatives. Urban forests and their management are connected to programs for improving air and water quality, flood control, energy conservation, microclimate control, aesthetic enjoyment, recreational opportunities, environmental education, and other goods and services in the urban environment. With the many benefits that urban vegetation can provide, the management of urban forests may be linked to an array of other urban initiatives, including urban renewal and community revitalization, economic development, community empowerment, and environmental education. Urban forests represent a critical link between people and forest resources. Ownership and use of residential holdings, as well as experience with public parks and forest preserves in urban areas, are how many citizens experience, appreciate, and learn about natural resources (Dwyer Nowak Noble and Sisinni 2000).
4.12.3. Dynamics Like all forests, urban forests undergo significant change with the growth, development, and succession of their biological components over time. The growth and development of urban forest resources occur, however, in the context of much more powerful and swift human-induced factors. Coupled with the relatively slow rate of tree growth and plant succession, the swift human forces for change make the dynamics of the urban forest particularly challenging for managers and users. The expansion and development of urban areas bring important changes in urban vegetation and other urban resources. Alterations to the distribution of land uses, intensity of urbanization, and population characteristics in urban areas result in different combinations of ground cover, increased or decreased opportunities for tree establishment and growth, changing environmental conditions, different resource-use patterns, and altered management objectives. New developments in transportation technology or manufacturing and service industries can bring considerable change to the condition, function, and management of urban lands and associated resources. The introduction of exotic plants and animals into interstate and international trade centers can have a profound influence on the urban forest, as has been the case with Dutch elm disease, gypsy moth, and the Asian long horned beetle. Changes in the composition of neighborhoods can prompt different approaches to the management of forests in residential areas, parks, and other open spaces. Urban trees are becoming more widely appreciated for their ecological, economic, social, cultural, and historical value throughout the urban environment (Dwyer Nowak Noble and Sisinni 2000). 4.13 Constraints and the need for improvement The preceding sections of this article highlighted the value of urban forestry. A number of important constraints, however, stand in the way of full achievement of this potential. Not all of these constraints can be removed, but they must at least be considered. 4.13.1. Inadequate funding A lack of funding is a major obstacle to systematic tree management and the promotion of more effective urban forestry programmes. Moreover, the situation is unlikely to improve, as municipal and national budgets continue to suffer economic restrictions, escalating inflation and resource shortages. Urban forestry efforts will therefore increasingly need to demonstrate that their benefits exceed their costs. This places emphasis on the need
for quantitative research on the positive results of urban forestry efforts. It will not be acceptable to claim that "trees reduce solar radiation", that "trees can absorb atmospheric pollutants" or that "trees can help alleviate fuelwood shortages"; specific data on costs and benefits will be essential (Nowak and McPherson1991). 4.13.2. Low priority Decision-makers (at both national and international levels) have tended to consider urban forestry as a low-priority activity and one more easily deferred than other programmes. This is partly a result of inadequate education, information, awareness and understanding regarding the economic, social and biological benefits of trees in the urban environment. Even today, urban forestry still tends to be regarded as a cosmetic, aesthetic amenity issue or as a luxury activity that is not worthy of support. Without political will, due attention to urban forestry and the realization of its full potential are impossible (Kuchelmeister and Braatz 1991). 4.13.3. Dispersal of tree management responsibilities Responsibility for the management of urban trees and forests is often shared by various administrative structures that have competing and even conflicting responsibilities. Because of the initial focus on aesthetic values, park and recreation departments are the agencies most commonly delegated primary responsibility but public works agencies, utility companies, environmental protection agencies, national forestry and/or agriculture departments may also be involved. Governments will need to establish lead agencies and ensure intersectoral linkages in order to make the best use of scarce financial and human resources (Kuchelmeister and Braatz 1991). 4.13.4. Lack of land The limited availability of land is a key constraint to urban forestry efforts. Urban sites are complex environments in terms of the availability of appropriate land for planting as well as in terms of ownership and tenure. In some cases, for example in extremely densely populated, unplanned urban fringe areas, the lack of land may be an absolute constraint. In others, people's participation may permit an efficient use even of scarce resources (Kuchelmeister and Braatz 1991). 4.13.5. Environmental stress
The urban environment is generally a harsh habitat for trees. Stress from the environment reduces the vigour of many tree species and increases their susceptibility to disease and pest infestation. Urban trees are subject to poor soils (compacted, low in organic matter, deficient in nutrients and moisture), air and water pollution and vandalism (Beatty and Heckman 1981). Species selection takes on paramount importance in overcoming these constraints. 4.13.6. Lack of training, extension and communication There are relatively few opportunities for training and education in urban forestry, particularly in developing countries, while a lack of appropriate instructional material is another constraint. As opportunities increase in the use of urban forestry as a tool for development, new skills will be required for urban vegetation managers. Foresters must learn to combine knowledge of trees with an understanding of city government and the needs of society. In addition to training to improve biological knowledge, there is a need for skills in ecological landscape planning, extension, communication and sociology and related subjects. Generally speaking, extension in urban forestry is very weak. Practical approaches are yet to be worked out in order to reach and involve citizens, especially the poor (Burch, Jr and Grove 1993). Networking has proved an efficient tool in research and development in many sectors, but formal global or regional urban forestry networking activities are extremely limited. One networking structure functioning on a global level is the International Union of Forestry Research Organizations (IUFRO) Project Group on Arboriculture and Urban Forestry. Other possible approaches to information exchange include: "twinning" arrangements between the urban forestry establishment of a city in an industrialized country and its counterpart in a developing country; and special programmes established by professional organizations through which city planning authorities, companies and individuals may contribute to a fund to subsidize the cost of collecting and disseminating information (O'Rourke 1990). 4.14. Management of urban forestry in Bangladesh The main objectives of managing urban forests in Bangladesh are- To Maintenance and sustenance of natural processes such as water, gaseous, nutrient cycles and support of flora and fauna, Provision of economic and social benefits, To get fuel wood and shade from urban forestry. Many of the general principles of arboriculture are applicable throughout the world, although specific management requirements will be dictated by such factors as the
species and climatic regime in question. A poor choice of species can be ameliorated to a certain extent by appropriate arboricultural treatment; for example, a tree which has grown too tall for its surroundings can be pruned. However, this is undesirable for tree health, aesthetically unappealing, and wasteful in terms of maintenance costs. It would have been far better to select in the first place a tree that only reaches a low height on maturity. Important arboricultural principles of general application include site preparation, tree establishment and early maintenance, tree surgery and protection, and the removal of tree waste. Each is discussed briefly here, drawing attention to recent changes in thinking and practice. The extent to which these principles are currently followed in Bangladesh is generally uncertain, although mention is made if any information on this subject was available (Carter 1993). 4.14.1. Site preparation As noted above, urban soils are often poorly suited to tree growth. Common problems are low levels of available nutrients, and high compaction due to the impact of human and vehicular traffic. This is compounded by low soil organic matter levels. The â€˜traditionalâ€™ response to this has been radical site amelioration prior to planting. Current thinking entails a more modified approach, depending on site conditions. In general, alleviation of soil compaction is seen as being more important than other soil treatments. This may be achieved in a number of ways, the most important being subsoil ripping of the planting site. Current arboricultural practice also places far more emphasis on choosing a species to fit the given site rather than modifying the site to fit the desired species (Carter 1993). 4.14.2. Tree establishment and early maintenance Plantation stock it is particularly crucial in urban settings to plant nursery stock of good form and quality, with a healthy root-to-shoot ratio. Saplings without this are unlikely to survive planting in compacted urban soils, but even if they do, they may become a hazard in later life, being more prone than trees with a well-developed root system to being blown over, or to other damage. Similarly, saplings which have damaged stems will grow into trees with an unbalanced branch system; this may not only look unsightly, but could be dangerous. The size of seedlings or saplings planted in urban situations is often considerably larger than those used in normal plantation forestry. However, the use of seedlings of no more than 60 cm height is now considered by many professionals to be sounder practice. They are often so much more vigorous than larger saplings that they catch up in size with the latter after a short period (Carter 1993).
4.14.3. Planting techniques Following site preparation, it is of course important to ensure that planting pits are dug to an adequate size, and preferable that they are prepared well in advance of, rather than at the moment of, planting. It may also be necessary to take into account the existence of underground utility services (water pipes, etc.) when planning where to plant. In professionally conducted urban plantings, particularly in the case of street trees, a variety of techniques may be employed to ensure good tree establishment and to guard against future problems (Webb 1991). 4.14.4. Watering and mulching Watering is often considered essential for the establishment of urban trees, but it may be very difficult to provide in some circumstances. One example is provided by tree growing in self-help housing areas where even drinking water is in short supply. Apart from taking the obvious precaution of timing planting to coincide with the beginning of the rains, and ensuring that the pit is at least well watered at the time of planting, various options may be considered. These include the use of drought-tolerant species, regular weeding, the application of mulch, irrigation (possibly using wastewater), and the incorporation at the time of planting of a pipe to facilitate water penetration (Carter 1993). 4.14.5Weeding Weed control may be affected either by manual weeding or by the use of appropriate herbicides, both before planting and on a regular basis afterwards. While the use of herbicides in the case of UK plantings is often recommended (Davies 1987), this may be less appropriate in developing countries for a variety of reasons, both social (employment generation may be desirable) and technical (herbicides may act differently in warmer, wetter climates). 4.14.6Staking In general, staking is no longer recommended in amenity plantings, as it inhibits the development of sturdy stems and can cause problems when finally removed. Forgotten stakes and ties can also badly damage growing trees. It is now considered preferable to plant seedling/saplings which are small enough to require no support (Patch 1987).
4.14.6. Tree surgery and protection Since the mid-1980s, arboricultural theory and practice in the Western world has been strongly influenced, if not “revolutionized”, by the work of the American arboriculturalist, Alex Shigo. While his ideas are not universally accepted or even necessarily new, his practical recommendations are now quite widely implemented in North America, Europe, Australia and cities elsewhere with a strong urban forestry programme such as Hong Kong. In Bangladesh these practice need to be started. Possibly the most celebrated of Shigo's theories is that of CODIT, Compartmentalization of Decay in Trees. CODIT is a model that describes a tree's defense system - its response to wounding. It is used to explain why traditional pruning regimes using flush cuts are bad for tree health, and that ‘Natural Target Pruning’ (NTP), cutting off the branch at an angle (leaving the branch collar, if one exists, intact), is better practice. CODIT theory is also used as an argument against treating wounds with a seal to guard against pathogens. In place of sealants, a variety of gel formulations with systemic fungicidal properties are now more commonly recommended (Clifford and Gendle 1987). It is uncertain to what extent the ideas of Shigo are put into practice in developing countries, although it is unlikely that they are widely known or followed. In general, knowledge and skill in tree surgery varies widely by country. For example, Hill (1992) reports that in Quito, Ecuador, poor pruning practices were attributed to excessive demand for services and poor tools, rather than lack of experience and skill. In South China, Jim (1991) have noted that despite quite high standards of tree selection and planting design, pruning is conducted with very scant regard to tree health. Johnston added that this was certainly not merely a reflection of a lack of suitable equipment. Timely and efficient tree surgery is one of the most important means of preventing the spread of disease in trees once it occurs, but good arboricultural practice also implies minimizing the possibility of pest and disease attacks. Attention to this in the early years of tree establishment, including an appropriate choice of species/provenance/cultivar is clearly important, as is the prompt and complete removal of any infected tree material (which should be duly destroyed).
4.14.7. The removal of tree waste Key issues in the removal of tree waste are public safety, utilization of removed material as appropriate, and (as mentioned above) limiting the spread of pests and diseases. In
Bangladesh, many urban authorities make use of tree prunings by shredding it for compost or mulch, and such recycling is becoming an increasingly important feature of urban forest management. Inevitably urban trees grow old and must be removed, or parts of them removed, before they cause any damage. Technically, there are often complications in this due to the close proximity of buildings and other urban infrastructure. However, perhaps the most important issue for urban foresters is advance planning - ensuring that removal operations are timed to avoid any public hazard, rather than responding to one (Carter 1993). 4.15. Management, structure and factors of urban forestry in Dhaka city Urban forestry needs multi-management approach. It does necessitate appropriate planning before embarking upon an urban forestry programme. The goals based on the local needs have to be determined in the planning phase. A management plan should serve to sustain psychological health for human perception as well as to maintain whole some environment (Zabala 1991). The primary objective of urban forest management is to maintain the health and vigor of the vegetation without undue interference of the city dwellers. Apart from others, urban forest management has three fundamental needs, tree planting, maintenance and removal. 4.15.1. Tree Planting The followings are the factors which should be considered for urban planting of trees. 220.127.116.11. Species-site selection The urban site is a complex environment where soil, temperature, moisture availability, pollutants etc. vary from one place to another. The species therefore, selected for planting at a given site must be adapted to it. 18.104.22.168. Species composition Diversification of species is needed. As a general rule, the species composition promotes species diversification by restricting a species to not more than 15% of the population. 22.214.171.124. Spacing of trees Determined by the local conditions, species, plant height, spread form and use. Spacing recommendation â€˘ Trees which attain bole dia greater than 30 cm when mature should be planted in space less than 1m. â€˘ Trees should not be planted within 10 m of an intersection.
• Trees should not be planted within 3m of utility poles or fire hydrants. • Large trees should be planted 12-18 m apart. • Medium tree should be planted a minimum of 10 m apart. • Small trees should be planted a minimum of 8 m apart. (Zabala 1991) 126.96.36.199. Selection of species Availability of space is the most critical factor in selecting tree species in cities since it is limited by buildings, overhead wires, curbs etc. So, tree species have to be selected considering the available space when these will mature. The following are some of the species which may be used in the urban forestry programme in Dhaka city. 4.15.2. Suggested tree species for a particular use The following are some of the species which may be used in the urban forestry programme in Bangladesh: Table188.8.131.52.: List of trees for used Energy conservation Local Name Akashmoni Kala koroi Gamar Eucalyptus Sada koroi Sissoo Ipil ipil Mangium
Scientific Name Acacia auriculiformis Albizia lebbeck Gmelina arborea Eucalyptus camaldulensis Albizia procera Dalbergia sissoo Leucaena leococephala Acacia mangium (SourceSattar1999)
Table 184.108.40.206.2: List of trees used roadside and avenue planting for beautification Local Name Sonalu Minjiri Krishnachura Polash Eucalyptus
Scientific Name Cassia fistula Cassia siamea Delinix regia Butea monosperma Eucalyptus camaldulensis
Used parts Yellow flower Yellow flower Red flower Red flower White flower
Eucalyptus Jarul Jacaranda Debdaru Jhau Neem Koroi Ashok
Lagerstroemia speciosa Jacaranda mimosa Polyalthia longifolia Casuarina equisetifolia Azadirachta indica Albizia procera Saraca asoca
Purple flower Blue flower White flower White flower White flower White flower Orange flower (Sattar 1999)
Table220.127.116.11: List of trees used Parks, memorials, etc. for shade
Local Name Raintree Simul Gora neem Bot Krishnachura Sissoo Kadam
Scientific Name Albizia saman Salmalia malabarica Melia azadirachta Ficus benghalensis Delinix regia Dalbergia sissoo Anthocephalus chinensis (Sattar
1999) Table18.104.22.168.: List of trees used Screening for hiding undesirable objects Local Name Nageshwar Akashmoni Shetkanchan Karamja Hizal
Scientific Name Mesua ferra Acacia auriculiformis Bauhinia variegate Pongamia glabra Pongamia glabra (Sattar
1999) 4.15.3. Maintenance of trees One of the primary concerns of urban forest management is to maintain the health, vigor and compatibility of vegetation with the environment. It involves all practices to control growth, damage from insects and diseases right from the time of planting to removal (Zabala 1991). 4.15.4. Growth control The objective of growth control are to retard or redirect and accelerate growth of trees, the forest objective may be achieved by pruning and application of growth retardant chemicals. The second one can be met by fertilization, irrigation and control of competing vegetation (Zabala 1991). 4.15.5. Pest and diseases The insects and diseases that attack the forest trees are also those which attack urban trees as well. The urban trees are generally high valued, and as such pest control is aimed at single tree, rather than simultaneous treatment of as trees as practiced in the forest plantations. Biological, mechanical and chemical controls are used for insect attack. In selecting the insecticides, attention must be given to city animals and human beings (Zabala 1991).
4.15.6. Removal The purpose of removal of trees from urban forests is to reduce the risk of injury to people and damage to property as well as to clean the surroundings of unsightly debris. Dead trees, hazardous trees, overcrowded trees, pruning debris, storm debris, stumps and leaves must be removed. Debris and leaves need to be collected when these fall on the roads, sidewalls, residential lawns, etc. in the plantations, these are not necessarily taken out as they add to the fertility of the soil once decomposed (Zabala 1991). 5. METHODOLOGY 5.1 Introduction In this study the main objective is to find out the relationship between land use change in DMP areas or zones (i.e. Ramna and Uttara) by using multi-spectral and multi-temporal satellite images towards sustainable land use management. The study also designed to find out the critical relationship between land use and vegetation change with climatic change. In order to reveal the changes of land use two date satellite images were used such as Land sat ETM 10 January, 2011 and ASTER 07 February, 2010 and to determine the climate change over 30 years data (1981-2010) of climatic factors such as temperature, rainfall, humidity and evaporation were collected and analyzed. After the identification of flood hazard thematic information from multi-temporal images then it was superimposed on land use change thematic map to determine the areas where the settlements were established by the urban people or peri-urban people to lead their life. The following steps are involved in this study to obtain the fruitful result by analyzing and processing of data for the study. The overall methodological framework was given in Figure 4.1 which represents the general methodology of work. Here general methodology of landuse classification and evaluation of the impact of climate change were given concisely. 5.2 Data Preparation for Landuse Classification Digital Image processing involves the interpretation and manipulation of digital images with the aid of computer. It is a very broad subject and procedures are mathematically complex. There are several operations needed for the processing of digital images (Lillesand et al. 2004).
First, the images were acquired and rectified. Rectification was done by using geometrically corrected image. Geometric correction addresses errors in the relative positions of pixels. It may be induced by sensor viewing geometry and terrain variations (ERDAS Field Guide 2002). The image was geometrically corrected with reference to previous image of 2005. At least 170 well distributed Ground Control Points (GCPs are specific pixels in an image for which the output map coordinates are known and consist of X, Y pairs of coordinates, to correct more complicated types of distortion higher orders of transformation can be used and more GCPs are needed for transformation process) are used in the rectification process. The Root Mean Square error is the distance between the input location of a GCP and the retransformed location for the same GCP and here the root mean square error (RMSE) varied from 0.25 to .45 pixels. Finally a first order polynomial fit ( a mathematical expression consisting of variables and co-efficient) was applied and all the data were resampled to 30 m pixel size for Land sat ETM and 15m for Aster by using the Nearest Neighbor Method. The Nearest Neighbor Method is used in which the output data file value is equal to the input pixel that has the coordinates closest to the retransformed coordinates of the output pixels. Such as to determine an output pixel’s nearest neighbor, the rectified co-ordinates (x₀,y₀) of the pixel are retransformed back to the source co-ordinate system using the inverse of the transformation (Figure 5.2). Urban Land use Change Determination of Land use Change Determination of urban landuse change Multispectral Image Processing Rectification and Georefencing Ground Truthing Multi-temporal Image Classification
Accuracy Assessment Analysis of Landuse data Analysis of relationship between Land use Change and vegetation Analysis of Climate Change due to landuse and vegetation change
Determination of land Use Change (Land sat’11) Determination of urban land use change(ASTER ’10)
Analysis of Digital Elevation Model (DEM)
Figure 5.1: Methodological Steps involved in data generation and analysis.
The retransformed coordinates (x₁,y₁) are used in bilinear interpolation and cubic convolution as well. The pixel that is closest to the retransformed coordinates (x₂,y₂) is the nearest neighbor.
(x₂,y₂) Nearest to (x₁,y₁)
Figure 5.2: Nearest Neighbor Method (source: ERDAS Field Guide 2002, p 347 For geo referencing Bangladesh Transverse Mercator System (BTM) was used as the coordinate system which is an area specific standard Universal Transverse Mercator (UTM) projection system for Bangladesh (Dewan and Yamaguchi, 2008). Besides, a number of Geospatial data including Metropolitan boundary, rivers and geomorphic units and elevation units have been constructed from various sources. 5.3 Data Preparation for the Climate Change Climate change is very critical issue as the digital data are not available widely. Bangladesh meteorological department collect weather data such as temperature, rainfall, humidity and evaporation etc. For the study, climatic data of about 30 years were collected and analyzed. The data were presented here in graphical format. The impact of climatic data
was critically assessed to determine the impact of climate change on the flood with reference to land use change. 5.4 Data preparation for urban trees and Shrubs For the data preparation of vegetation, we simply used Remote sensing technology to classify the coverage. We also collected Average 30 sample location of urban green tree places like Uttara and Ramna to identify the species. Geographic Information Systems (GPS) used for this purposes. Then we put it into GIS environment (Arc GIS 9.3.1 and ERDAS Imagine 9.2) and analyze with the help of those tools. At last we assessed landuse and vegetation coverage of Uttara and Ramna area. Land use classification maps are an effective way to observe spatial pattern from Remote Sensing multispectral image data. The objectives of image classification procedures are to automatically categorize all pixels in an image into land cover classes or themes. Normally multispectral data are used to perform the classification and indeed the spectral pattern present within the data for each pixel is used as the numerical basis for categorization. That is different feature types manifest different combinations of Digital Numbers (DNâ€™S) based on their inherent spectral reflectanceâ€™s and emmittance properties. (Lillesand et al. 2004). Land cover/ Land use classification is used to detect and analyze the spatio-temporal pattern and change of lands at various spatio-temporal scales. The term land cover means the vegetational and artificial covering of land that is physical conditions of the ground surface and the term land use includes the dimension of manâ€™s activities on land which are directly related to the land (Townshed 1981). The uses of Land cover is increasing alarmingly in urban areas of developing country like Dhaka city. The rampant urban sprawling exerts great pressure to roads, housing and employment opportunities. Thus, the quality of the environment degrading due to uncontrolled growth and abusive manner of urban population. Human being is involved in encroaching lands through clearing the natural vegetation cover. They are also filling up the agricultural lands and wetlands by destroying the ecosystems and biodiversity of the surrounding urban area of Dhaka city though this agricultural lands meet up the most demands of agro-products to the urban people.
This rapid urban growth and transformation of rural lands to built up areas such as roads, commercial areas and infrastructures becomes crucial concern that can contribute to the increase of landlessness and jeopardize the economy (Dewan et al. 2006). Rapid urbanization also led to the deterioration of environment, particularly mounting flood risk potential, severe environmental pollution and spectacular growth of informal sector settlements (Dewan and Yamaguchi 2008). No
Land cover types
Urban/ Built up
Level 1.1 Residential 1.2 Commercial & Service 1.3 Industrial 1.4 Transportation, communication &
utilities 2.1 Cropland
2.2 Orchards, nurseries & horticultural 3.1 Deciduous areas 3.2 Evergreen
3.3 Mixed forest land 4.1 Streams & canals
4.2 Lakes 5.1 Forest land
5.2 Swamps, bogs, marshes etc fill/Vacant 6.1 Sandy areas 6.2 Bare soil/open space
Table 5.1: The landcover types and level which were adopted from Lillesand et al. (2004) for the study purpose. 5.5 Landcover Classification Algorithms Multispectral classification is the process of sorting pixels into a finite number of individual classes or categories of data, based on their data file values. Depending on the type of information original data are extracted and classes are associated with known features of the ground. Standard classification algorithms involve with the following steps:
Here, the steps represent the procedures of image classification. Standard image classification for my study purpose used only supervised classification process and this process is very useful for land cover classification. Supervised classification is used basically for quantitative analysis of remotes sensing image data and rests upon using suitable algorithms to label the pixels in an image as representing particular ground cover types or classes (Richards, 1993). The designated bands (Table 5.2) and Standard Land cover types (Table 5.1) were used for the study purpose. The used band combinations are 4, 3, 2 for Land sat and 1, 2, 3 (VNIR) for ASTER image. Supervised training/classification is controlled by the analyst with particular algorithms and unsupervised training is more computer-automated as it is depended upon the less known data. A set of signatures defines a training cluster corresponds to a class and is used with a decision rule to assign the pixels in the image file to a class based on parametric and non-parametric statistical rule. After defining the signatures, the decision rules enables actual sorting of pixels into distinct class of values. The classified maps are shown in Figure 5.1 and 5.2. Land sat ETM List
ASTER (VNIR) Principal
Wave length (Îźm)
(Îźm) Band 1
penetration Band 2
Water body and analysis
vegetation. Band 3
Design to sense Red
Determining vegetation types, delineating water bodies.
Infrared Band 5
Indicative of vegetation moisture content
Infrared Band 6
Vegetation stress analysis & Thermal mapping analysis.
Useful for discrimination of mineral, rock types
Table-5.2: Landsat ETM (Enhanced Thematic Mapper) and ASTER (Visible & Near Infrared) Thematic Mapper Spectral Bands. Source:Lillesand et al. (2004). To extract useful land use classesâ€™ ground truthing (acquisition of knowledge from field work) data were collected by using global positioning system (GPS) though a number of errors and inaccuracies also remained. Training samples (a set of pixels) are obtained through digitizing polygon (represents area of interest (AOI) or known ground information) and autoassisted high degree of user control by evaluating the accuracy of the signatures. On the other hand, unsupervised training requires only minimum initial input and it is also known as clustering through ISODATA clustering (Iterative Self-organized Data) and RGB (Red, Green and Blue) clustering. The ISODATA clustering uses spectral distances but iteratively classifies the pixels and redefines the criteria of each class as in the sequential method. The RGB clustering plots pixels in three dimensional feature space.
Figure 5.1: Landuse/ Landcover Classification of Dhaka Metropolitan Area Using ASTER image of 2010
Figure 5.2: Landuse/Landcover Classification of Dhaka Metropolitan Area Using Landsat ETM Image of 2011
Nonparamatic Kappa Coefficient
Digital Image Classification 4. Evaluating Signature Creating Signature Decision Rule Supervised Signature
2. Unsupervised 1. Supervised Parametric Selecting Training Sample Unsupervised Signature Digitized User Defined Polygon Identify Seed Pixel Create Non-parametric Signature Evaluate Feature space Signature 3. Creating Signature File RGB Clustering
Clustering Non-parametric Parametric ISO data clustering
5. Signature Manipulation Jefries-Matusita Distance Separability
Using signature Data
7. Classification Decision Rule Parametric & Non-Parametric Maximum Likelihood/ Bayesian Decision Rule
8. Accuracy Assessment Non-parametric Parametric 6. Fuzzy Classification Random Reference pixels Error reports 9. Output
Figure 5.3: Schematic classification Procedures (compiled from Lillesand et al. 2004 & ERDAS Field Guide 2002) So, in supervised technique once signatures are created that can be evaluated, modified and manipulated. Signature reparability measures the distance between two signatures and calculated by using Jefries-Matusita distance (a function of separation between spectral class means) technique. After significantly signatures has been evaluated then performed classification of data by using Maximum Likelihood algorithm which assumes that the histograms of the bands of data have normal distributions. It is apparent that pixels are not always distinct but it is rather mixed make-up. When data are obtained that contained two or more categories of data and Fuzzy classification method takes into account that there are pixels of mixed make-up. Class
ASTER’2010 Produce User’s
Landsat ETM’2011 Produc User’s Area
n Agricultu re Wetland
8 53 Landfill 86.8 90.0 32.1 7.7 83.2 89.3 32.4 7.8 Total 416.5 100 416.5 100 Table 5.3: Accuracy Report and Classification of recent satellite images (Land sat ETM’11and ASTER’10) for the study. Accuracy assessment is a general term for comparing the classification to geographical data that are assumed to be true basically it is done by assuming-true data are derived from ground truth data. Therefore, a set of reference pixels (points on the classified image for which actual data are known) is used and more than 250 reference pixels (stratified random pixels) are needed to estimate the mean accuracy of a class to within plus or minus five percent. From the accuracy assessment ‘Error Matrix’ report is derived and to express the proportionate reduction in error generated through classification process compared with the error of a completely random classification. In my study classification overall accuracy was obtained 85.07% for Land sat ETM’08 and 88.82%for ASTER’10 image. The report and classification are presented here in table 5.3. The overall Kappa co-eficient is 0.8517. 6. DATA COLLECTION 6.1 Ramna Green Space: Ramna Thana (DHAKA district) with an area of 7.85 sq km, is bounded by Tejgaon and KHILGAON
thanas on the north, LALBAGH and KOTWALI (Dhaka) thanas on the south, MOTIJHEEL and
Khilgaon thanas on the east and DHANMONDI thana on the west. Ramna Lake is located on the west side of the thana. Ramna area comprises with shabagh, Sohorawordhi Uddyan, Ramna Park and Dhaka university areas. The green space serves the city as a unique recreational space. It also serves the people various environmental including landscape, recreation, education and general well being and a habitat for wildlife.The basic importance of Ramna area is that it acts as a great temperature absorber of Dhaka city. The change of climatic phenomena is greatly modified by the park’s multifarious trees. Population 195167. Land use Urbanisation 100%. Agricultural land 2%, residential 35%, commercial 20%, business centre 8%, office establishment 30%, public use 2%, low marshy land 1%, fallow land 1% and others 1%.
GREEN AREAS IN DHAKA CITY Legend Area
Others Field Graveyard Park
Figure 6.1: Green Areas in Dhaka City showing Ramna and Uttara Green Space
6.2 The GPS Location of various trees at Ramna Area: There are 30 sample location of trees were collected using GPS. These are the dominant species in Ramna area. The table shows the variations of trees species of Ramna area. Sl No 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
Latitude 234403 234402 234401 234401 234359 234401 234402 234359 234358 234400 234402 234404 234403 234302 234404 234403 234402 234404 234403 234401 234258 234105 234407 234407 234406 234405 234403 234401 234411 234412
Longitude 902329 902330 902329 902328 902328 902335 902341 902341 902346 902348 902349 902359 902359 902358 902400 902359 902357 902356 902358 902357 902345 902347 902404 902403 902402 902404 902401 902402 902409 902413
Name of Tree( Local) Koroi Mehogoni Koroi Koroi Koroi Mehagoni Jarul Rain Tree(Koroi) Mehogoni Koroi Mehagoni Mango Rain Tree( Koroi) Mehagoni Mehagoni Mango Coconut Banyan Tree Koroi Jack fruit Banyan Mango tree Akash moni Mehagoni Acacia Jarul Shimul Mango Shimul Acacia
Scientific Name Albizia lebbeck Swietenia mehagani Albizia lebbeck Albizia lebbeck Albizia lebbeck Swietenia mehagani King Lagerstroemia speciosa Albizia saman Swietenia mehagani Albizia lebbeck Swietenia mehagani King Mangifera indica Linn Albizia saman Swietenia mehagani King Swietenia mehagani King Mangifera indica Linn Cocos nucifera Ficus benghalensis Albizia lebbeck Artocarpus heterophyllus Ficus benghalensis Mangifera indica Linn Acacia auriculiformis Swietenia mehagani King Acacia auriculiformis Lagerstroemia speciosa Salmalia malabarica Mangifera indica Linn Salmalia malabarica Acacia auriculiformis
6.3 Uttara green space: Uttara Thana (DHAKA district) with an area of 36.91 sq km, is bounded by GAZIPUR SADAR upazila on the north, PALLABI, CANTONMENT and BADDA thanas on the south, RUPGANJ upazila on the east and SAVAR upazila on the west. Population 108077; male 54.41%, female 45.59%; Muslim 96.10%, Hindu 3.32%, Christian 0.49% and others 0.09%; population density per sq km is 2928.Land use Urbanization 100%. Residential, commercial, business, educational, office, etc 81%, and low
lying marshy land 19%. Main crops Paddy, vegetables. Extinct or nearly extinct crops Aus paddy, jute, wheat and oil seeds. Main fruits Mango, jackfruit, black berry, coconut, banana. Fisheries, dairies and poultries Dairy 57, fishery 13 and poultry farm 27.
6.4 The GPS Location of various trees at Uttara Area: There are 30 sample location of trees were collected using GPS. These are the dominant species in Uttara area. The table shows the variations of trees species of Uttara area. Sl No
Name of Tree( Local)
Mangifera indica Linn Swietenia mehagani
9 10 11 12 13 14
235158 235157 235156 235154 235152 235149
902322 902323 902324 902325 902325 902325
Coconut Banyan tree Mehogoni Mango Mehogoni Mango
Cocos nucifera Ficus benghalensis Swietenia mehagani Mangifera indica Linn Swietenia mehagani Mangifera indica Linn
18 19 20 21 22 23
235154 235247 235246 235153 235153 235348
902347 902333 902332 902324 902322 902321
Mango Jackfruit Jarul Mehogoni Boroi Mango
Mangifera indica Linn Artocarpus heterophyllus Lagerstroemia speciosa Swietenia mehagani Zizyphus mauritiana Lamk. Mangifera indica Linn
24 25 26 27 28 29 30
235446 235047 235046 235147 235146 235051 235044
902315 902315 902326 902328 902327 902357 902330
Koroi Mehogoni Mango Jarul Mehogoni Boroi Jarul
Albizia lebbeck Swietenia mehagani Mangifera indica Linn Lagerstroemia speciosa Swietenia mehagani Zizyphus mauritiana Lamk. Lagerstroemia speciosa
6.5 Species found in the location: Uttara and Ramna The study shows that in location Uttara and Ramna different species with the Mehagoni (Swietenia mehagani King) as a common species in the two locations. Due to this diversity of tree species, urban forests can mitigate urban heat island effects and conserve cooling energy by shading buildings and other heat-absorbing surfaces, as well as lowering summer air temperatures through evapotranspirational (ET) cooling (Meier 1990/91). Trees can save space-heating energy by reducing wind speeds, thereby reducing the amount of cold outside air that infiltrates buildings (Heisler 1986). In Dhaka city these diversity of tree species help the tolerance to pollution. For example, the tolerance to pollution and other urban environmental stresses of Platanus acerifolia (London planetree, or hybrid plane), a tree widely planted in European cities, is well recognized in China, where it is widely cultivated in warm temperate and to a lesser extent in sub-tropical cities (Jim 1991). In countries (e.g. Germany), where timber is harvested from peri-urban forests, the major management objective is providing recreation/education of the urban dweller, and timber harvesting operations are significantly modified accordingly. Largely having been conceived initially in terms of landscape improvement and amenity provision, urban forestry is now increasingly concerned with other, additional benefits, such as the control of air and noise pollution, and microclimatic modification (Carter 1993). One of the major problem in the Dhaka city is that air is either of foul odor or contaminated with dust and chemicals emitted by many industries and innumerable vehicles in the city. These diversity species can help to reduce air pollution. One example is provided by Mexico City, where the average
level of particulate suspension in the atmosphere has risen from 65 mg/m 3 in 1974 to 400 mg/m3 in 1990. Over the same time span, atmospheric sulphur dioxide levels rose from 60 mg/m3 to 120 mg/m3 (Chacalo and Pineau 1991). Air pollution may be compounded by local conditions, notably air inversions (warm air lying over cold air) which trap polluted air over cities or towns for prolonged periods. Examples of this phenomenon include Mexico City and Kathmandu, Nepal. Again many countries practices urban forestry only few purposes. For example- in Debre Birhan, Ethiopia - Growing trees for fuelwood, Hong Kong - Maximizing the use of space, Tashkent, USSR - An international array of trees, Milton Keynes, UK - Trees as investment, Singapore, Republic of Singapore - Aerating a concrete jungle, Brussels, Belgium - The forest of the sun, Kampala, Uganda - Fuelwood and ornamentals, Dunedin, New Zealand - Logs and loans, Beijing, People's Republic of China - Continuing an ancient tradition (Haque 2003). Although the potential of these processes has not been well documented in Dhaka city of Bangladesh, studies have been conducted in other cities round the world (Akbari and Taha 1992 McPherson 1993). 7. DATA ANALYSIS 7.1 Comparative Analysis Land cover / Land use classification is very useful to delineate the spatial pattern of land use scenario. Again, satellite image provides more accurate data of the land use changes. In my study two multi-temporal images were employed to extract the land cover condition of Dhaka city which was also done by Dewan et al. (2008) and Ahmed B (2010). Among them Dewan et al. (2008) studied land use change broadly from 1960-2005 and Ahmed (2010) studied
land cover condition of 1999 and 2009 by using Markov Cellular Automata
approach. Their study was considered here for comparative analysis of land cover change was presented in table 5.4.Ahmed (2010) found that the built up area has increased distinctly and in unplanned manner.The decrepitude of vegetation,wet land and fallow land also noticed and predicted.The condition of waterbodies are worsening in condition though he found difference by using Markov Cellular Automata (CA Markov) modelling. A detail study was conducted by Dewan et al. (2008) to estimate the land cover change of Dhaka city and he found that the water body, vegetation and wet land is in decreasing trend.
It was shown by the study that built up area and land filing activities are increasing in a haphazard way. In my study, it was emphasized on the recent and updated information of the land over change of greater Dhaka city from 2008-2011. It reveals that the built up area and land filing by encroaching and forcefully filled are increasing in a drastic manner where as the water body, wet land and vegetation are decreasing in an alarming way without considering the environmental regulations of conservation and management. So the studies are combined here and graphically presented (Figure 7.1) to obtain real
416.5 100 416.5 100 416.5 100 416.5 100 416.5 100 416.5 100 416.5 100
7.8 32.49 3.0
4.3 32.18 7.4 18.2 1.2 12.5
12.3 52.88 91.24 22 71.28 17.2 54.49 13.3 32.5 131.55 31.6 127.15 30.6 107.97 26
13.4 54.64 33.3 120.40 29.0 90.24 21.7 85.74 20.6 84.66 20.4 42.37 15 64.55 14.3
14.7 65.85 15.8 57.93 13.9 43.91 10.6 39.92 9.6 37.73 4.3 27.89 6.7
6.5 7.1 29.76 7.2 21.01 5.1 18.86
55. 8 11.1 55.50 13.4 108.58 26.1 144.86 34.9 161.04 38.7 205.49 49.4 213.4 51.3 231.93 5
20.50 4.9 21.01 5.1 23.08 5.8
% Area % % Area % Area % Area % Area % Area % Area
features of land cover or land use change of Dhaka city for best analysis.
Area Land cover Type
Table 7.1: Land use/ Land cover type of greater Dhaka city showing the comparative change from 1960-2010. Areas are in KmÂ˛. The table was adopted from Dewan et al. (2008); Ahmed B (2010) and recent classification was done by the Author using Land sat ETM (2011) and ASTER â€˜10).
Figure 7.1: The changing trends of land cover types of Dhaka city 1960-2010. 7.2 Analysis of the Landcover / Landuse Change Dhaka is the mega city in the country, enjoys distinct primacy in the national urban hierarchy (Islam 2005) and this primate city is now expanding towards south to north-eastern direction (Ahmed 2010) that is one directional growth. Historically, the direction of urban expansion of Dhaka has greatly been constrained by the low elevation of lands (Dewan et al. 2008) and depressed depositional flood plains of Dhaka. This is happening by converting the space into multifaceted land use patterns. Thus major developed establishment was on high and medium madhupur terraces. It reveals that the transformation of land to built up areas from converting water bodies, wet lands and vegetation etc. The crucial features of land use change is that people encroaching the land by earth filling and constructing different types of religious places on the bank of river side, wetlands and water bodies etc. The infringement of agricultural land to residential and commercial purposes is largely results in the worsening condition of urban sprawling. Another vulnerable situation is that the conversion of vegetation covers. People are fallowing lands in drastic manner without considering the future demand of urban livelihood as observed in field visit. It is obvious from the above table 7.1 and graph 7.2 that the built up and land fill categories have been increased significantly. Such as the built up areas increased from 46.25231.93 ²km which is 11.1 to 55.8% of land cover during 1960-2011. The land fill category increased 49.8-32.49 km² which is 1.2 to 7.8 % of land cover during the same time. The amount of wetland and water body is decreasing drastically. It is observed that the amount of wetland was 135.14 km² (32.5%) in 1960 which is decreased to 52.8 km² (12.53%). Again, the diminishing water body warns the urban planners to surmise the future
water crisis and drainage capacity during monsoon season of the city. The shrinking condition of rivers is very critical as the ‘Carrying capacity’ of them is decreasing with time interval. The water body (pond, river, Lake Etc) is slightly decreased from 29.65-25.04 km² and in percentage from 7.1 -6.5% though it is different from the real situation. On the other hand, the vegetation cover changes show the negative trend (Ahmed 2010) which is from 61.09-18.65 km² (14.7%-4.8%) and this cover was mostly changed into built up areas. Land Cover types (%) 1960 1975 1988 Bulit up 11.1 13.4 26.1 Water bodies 39.6 38.8 35.7 Vegetation 14.7 15.8 13.9 Agricultural Land 34.5 32 24.2 Total 100 100 100 Table 7.2: The predicted land cover change of
1999 34.9 30.5 10.6 24 100 Dhaka
2003 2005 2010 2011 2030 38.7 49.4 51.3 55.8 66.3 26.9 22.3 19.6 19 15.2 9.6 4.3 6.78 4.8 3.6 24.8 19.3 22.4 20.9 16.59 100 100 100 100 100 city using Landsat ETM’2011and
Figure 7.2: The predicted changing trends of land cover types of Dhaka -city. Again, if we categorize the land cover into four types (Table 7.2 and Figure 7.1) then the following situations would be resulted. From the graph, the land cover change indicates that the built up area is increasing with the cost of wet land, water bodies and vegetation covers. The cultivated land is degrading by land filling and extending residential areas. It is seen that about 10.9% agricultural lands were converted to built up areas where as about 9.8 % vegetation cover and 19.8% water bodies were also converted. However, in near future about 66.3% area will be converted into built up area and water bodies and agricultural land will also be decreased simultaneously. In contrast to the above unnatural activities, there is another most important noticeable activities were found during the field investigation. There are about 290 or more real estate development companies are operating at Dhaka city to convert and develop the urban and peripheral lands to multi-facet activities. They are the most responsible community who are degrading the agricultural lands which is the mainstay of food sectors and wet lands of fringe and peripheral areas of Dhaka city.
The amplification urban land use change is rapid on the land cover due to rampant sprawling and environment deterioration. The process of urban expansion is detrimental to the environment and particularly, the increase of flood risk susceptibility (Dewan et al. 2008). Moreover the increasing slums and squatter at the fringe zone who is most vulnerable people to flood risk are worsening the situation by creating unplanned establishment. Again, the construction of 32 km Buckland embankment/ Buriganga embankment on the western side and 28 km embankment on the eastern side (DND) together with the proposed Eastern bypass encourages people to set up establishment in flood plain areas of Dhaka city as observed during field study. So, to properly manage this megacity urban expansion should be controlled on wetlands, water bodies, vegetation and floodplains. The classification of two high resolution multi-temporal images provided more accurate data in comparison to previous study. The study was further validated with the previous studies of different authors and organizations. The accuracy assessment is satisfactory and highest accuracy obtained by using ASTERâ€™ 2010 image which would be very useful for the future planning of Dhaka Metropolitan Area
7.3 Comparison between Uttara and Ramna Area
Figure 7.4: Landuse/Landcover Classification of Dhaka Metropolitan Area (Ramna Area) Using Landsat ETM Image of 2011 Figure 7.5: Landuse/Landcover Classification of Dhaka Metropolitan Area (Uttara Area) Using Landsat ETM Image of 2011.
Landsat ETM’2011(Ramna) Producer User’s Area s
Landsat ETM’2011(Uttara) Producer User’s Area % s
7 So it is observed that 40.7% of Ramna comprises with vegetation where as Uttara 76.7% areas are occupied with vegetation, though they are economically and environmentally important place in Dhaka city. 7.4 Climate variables and its impact Determination of Climate variability and its impact is a complex issue. It is obvious that world’s climate is changing and it is creating various drastic impacts on land and human activities. Among the various phenomenon of climatic change global warming i.e human involvement is very crucial. As we know global warming is largely because of certain long lived industrially and agriculturally generated atmospheric trace gases. These gases trap some radiant heat that earth emits after receiving solar energy to contribute in greenhouse effects and fortunately Bangladesh has a little contribution (Ahmed 2009). The levels of carbon di-oxide (CO2) have increased 40% over the last 200 years and currently at the highest level than at any time within the last 750,000 years. The Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC 2007) predicted that global climate system is unequivocal and global average near-surface temperature rose 0.74±0.18ºcelcius in the last century. It also warnned that sea-levels will probably rise by 18 to 59 cm with frequent warm, heat waves, heavy rainfall and cyclones and extreme high tides(Bhattacharya 2009). The thermal expansion of oceans and melting of ice together will cause sea-level rise and some low laying countries of the world including coastal parts of Bangladesh will be submerged. A rise of a 0.4ºc warming in the last century has apparently lead to a 5 cm rise in
the sea-level is predicted to rise in the order of 1m by the year 2100. (Ahmed 2009). The Global atmospheric Carbon di-oxide (CO 2) -equivalent concentration of the six greenhouse gases that included in the Kyoto Protocol (i.e. CO2, CH4, N2O, HFC, PFC, SF6) and Chlorofloro carbon (CFC’s), Ozone and various cooling aerosoles have increased markedly as a human activities since 1750-2011. The following Figure 7.4 shows the projected concentrations “kyoto” greenhouse gases (EEE 2011, Bhattacharya 2009). Figure 7.4: Measured and projected concentrations of "Kyoto" greenhouse gases: 17502100. Source: European Environment Energy, 2011 7.5 Climate Change and Bangladesh Climate is the average condition of the atmosphere near the earth’s surface over a long period of time considering temperature, precipitation, humidity, wind, evaporation and moisture content etc. The climate of Bangladesh is characterized by high temperature, heavy rainfall, often excessive humidity and fairly marked seasonal variations as it is located in the tropical monsoon region. Reversal wind circulation between summer and winter is the striking feature which is an integral part of south Asian climatic system. With three distinct seasonal variations (Dry season-November to February, Pre-monsoon-March to May and Rainy season-June to October), it is characterized by high ranges of temperature 7º-40ºc, wind 3-16 km/hr, pressure 1,005-1,020 millibars, relative humidity 57-80% , cloud cover 7590% and rainfall 150 -400 cm throughout the country. With these high ranges of variations makes this country more vulnerable to atmospheric disasters (Banglapedia, 2008). Bangladesh is one of the most climate vulnerable countries in the world as 75% of it is less than 10 meters and 80% is flood plain which makes it more disastrous country than other low laying countries of the world.
As geographically it owned funnel shaped coast and located at the footstep of Himalayan ranges, so it experiences various hazard i.e cyclone, tornado, storm surges and catastrophic climatic phenomena flood etc ( Papaioannou, 2000). However, it was manifested over the last two decades that it ranked high at risk mostly for tropical cyclone, nor’westers, tornadoes and flood. Among them flood is most disastrous climatic occurrence as every year it flooded about 26,000 square kilometers (around 18%) of the country, killing over 5,000 people and destroying over 7 million homes.
During 1998’s flood, 75% of the country including capital Dhaka city was flooded and this volume is 95% of total annual inflow (The Daily Star 14th October 2011). On the other hand, sea-level rise (SLR) is another vulnerable ingredient of climate change. According to the geological surveys, a rise of the sea level by 1m implies submergence of about 15 percent of Bangladesh’s landmass (Islam 2009). The consequences of SLR are that 2, 5086 square kilometer area will be submerged; 5 million people will lose their habitat and migrated to urban areas. Moreover, the salinity intrusion due to sea-level rise will harm agriculture, vegetation, flora and fauna i.e extensive biodiversity loss etc (Nishat 1998, khalequzzaman, 2010, IPCC 2007). So, it can be said that climate change is increasing the frequency and severity of natural hazard especially cyclones and floods. The reason behind this disastrous situation is largely because of geological, hydro-meteorological, biological and by social factors such as unplanned urbanization and indiscriminate manipulation of natural resources. 7.6 Climate Variability and Dhaka City Meteorologically, Dhaka lies at the micro climatic sub region of south-central zone (Banglapedia 2008) of Bangladesh. With three distinct season Dhaka city has remarkable features as winter (November-February) with temperature 10-20°c , pre-monsoon(MarchMay) with hot temperature reaching up to 40°c and the monsoon (June-October) very wet with temperature around 30°c. Dhaka experiences about 2147mm of rainfall of which around 80% falls during the monsoon time. As a microclimatic region, it can be analyzed by considering the combined effect of temperature, rainfall, humidity and evaporation of previous years to observe the impact of climatic change on this region. However the range of variations of climatic factors at this micro region is not highly distinguishable but it has major impact on agriculture, land use, economy and human health etc. It is observed that the temperature is increasing day by day as increasing population contributing to change the land cover by establishing infrastructure there. Again, Rainfall-another variable of climate is showing the decreasing trend which has great impact on urban livelihood. Urban life would be unbearable if this drastic trend of climatic variable sprint over time. However, this mega city has a little contribution on global climate change by creating global warming in consideration to other contributing countries as it is not an industrially developed country but it is experiencing. As we observed from the Digital Elevation Model (DEM) of greater Dhaka that about 60% area lays in between 1-6 meters above sea level and
this area frequently submerged due to perennial flooding. These geologically depressed areas hold water for weeklong by inundating built up (residential and commercial) and cultivated areas with a 1-1.5 meters depth of water. A national green house gas inventory for Bangladesh revealed that the energy sectors contribute more than 60% of the total GHG’s of 15,178 Gigagrammes per year. The contributing sectors are industries (35%), transport (17%) and residential sectors who are the key consumer’s of different fossil fuels. Having Multiplicity of sectors of Dhaka, it consumes electricity of which more than 85% generated from natural gas, gasoline, diesel-fuelled generators, petroleum and compressed natural gas. (Alam and Rabbani 2007) It must be noted that the surrounding brick kilns and land fill sites also contributes to global green house gases though the total amount of contribution is negligible but not inconsiderable as population and land use rate indicates that the contribution of Dhaka increasing. 7.7 Rainfall Variability and Climate Dhaka has faced a number of severe flooding in previous years since its establishment due to erratic and excessive rainfall. Excessive rainfall creates serious problems by inundating the surrounding area for several days due to drainage congestion and inadequate pumping facilities to remove the stagnant water. It also creates water logging to the built up areas which are developed mostly in unplanned manner. The water depth in depressed areas may be as high as 1-1.5 meters. Rainfall analysis of previous 30 years (1981-2010) reveals that the annual average rainfall of Dhaka is about 2147 mm and monthly average rainfall is about 350-450 mm. It also observed that flooding year average rainfall is 2300-2400 mm but non-flooding year average rainfall is about 2500-3000 mm. So it can be said that excessive rainfall is not the only cause of flooding in Dhaka city. Again, the number of ‘months without rainfall’ is increasing such as from 1981 -2010 about 54 months did not experience any rainfall. So days without rainfall is increasing (Alam and Rabbani 2007) though it is not affecting the average annual rainfall. On the other hand, the trends of rainfall exposing that it is decreasing with the time. The following Figures (Figure: 7.8, 7.9 and 7.10) show the variability of rainfall. The classification was done according to Banglapedia for Dhaka city to analyze the climatic factors more conveniently. 7.8 Annual Rainfall Variations
Figure 7.8: Rainfall Variability from 1981-2011 showing the Changing Trend line. 7.9 Winter Rainfall Variations
Figure 7.9: Winter Rainfall Variability from 1981-2010. 7.10 Pre-monsoon Rainfall Variation
Figure 7.10: Pre-monsoon Rainfall Variability from 1981-2010.
7.11 Monsoon Rainfall Variation Figure 7.11: Monsoon Rainfall Variability from 1981-2010. It is observed from the above graph (Figure 7.11) that monsoon rainfall is three times greater than winter rainfall and average pre-monsoon time rainfall does not show high variation. It may be noticed that the rainfall month is shifting from August to September as more rain is falling at September than August. So, Excessive rainfall is not only causing flood in Dhaka city. The high flood plain and depression deposit areas developed with younger natural levee deposit are remained inundated during moderate to low flooding. Besides the natural situation the poorly drained and low elevated areas holds flood water. Unplanned urbanization, haphazard establishment, land encroachment and filling by transcending low are the behind reason of flooding. Erratic rainfall affects the livelihood of urban people basically to the fringe and peripheral people of greater Dhaka region. 7.12 Temperature Variability and Climate Change Being a uniformly hot, humid and tropical monsoonal microclimatic region it is characterized by high variations of temperature and fairly marked seasonal variations. The
climate is partly dominated by summer and winter winds which controlled seasonal changes of temperature. The Urban climatic scenario is quite complex thing as it has to play multifaceted activities. Temperature is one of the strongest ingredients of climatic change and urban areas are mostly responsible for this situation. As the number of urban areas increasing in recent times so they are exposing themselves to climate change. The climatic conditions of Dhaka in terms of temperature is highly variable as the annual variations of minimum and maximum is very high (Figure 7.12). The highest minimum annual temperature observed 6.5°c in 1995 where as highest maximum temperature was 39.6°c in 2000. Figure 7.12: Range of Annual Temperature variations (minimum and maximum). 7.13 Temperature Variations: Minimum The annual minimum temperature graph (Figure 7.12) showing the decreasing trend of temperature and which is not strongly linearly correlated (R² = 0.051). Monthly variations of Seasonal minimum temperature reveal the highly changing nature. The eighty decade started with minimum temperature of 10°c and in the early of 21 st century it is showing decreasing trend with minimum 9.6°c. In winter season, January is the coldest month and February shows highly undulating trend of temperature over the most period of the year. In pre-monsoon time, April started with minimum 14.7°c-31.3°c with increasing trend. Again, temperature variations at monsoon time didn’t show so much variation than average. 7.14 Annual and Monthly (Minimum) Temperature Variations Figure 7.14: Annual Temperature Variability from 1981-2010.
7.15 Winter Temperature Variations Figure 7.15: Winter Temperature Variability from 1981-2010. 7.16 Pre-monsoon Temperature Variations
Figure 7.16: Pre-monsoon Temperature Variability from 1981-2010.20 7.17 Monsoon Temperature Variations Figure 7.17: Monsoon Temperature Variability of Dhaka City from 1981-2010. 7.18 Temperature Variations: Maximum Urbanized Dhaka is experiencing increasing temperature with the time of land use and climate change era. In early decade of 1980’s the maximum temperature was 36.5°c which is also known as commencing period of industrialization in Bangladesh (Islam 2005). After four decade of development the temperature reaches upto 39.6°c marking augmentation of 3.1°c temperature. So it can be said that temperature is rising. 7.19 Annual and Monthly (Maximum) Temperature Variations Figure 7.19: Annual and Monthly Temperature Variability from 1981-2010. In consideration to winter maximum temperature, it is noticeable that the temperature is slightly increasing (27°c-29°c) but in February it reaches it’s highest mark of point 35.9°c (Figure 7.19). During the pre-monsoon time, the temperature ( 34°c-39.6°c) shows highly undulating trend by reaching up to 39.6°c demarking as a hottest month of the year. Again, the monsoon temperature also shows variability considering increasing trend. 7.20 Winter Temperature (Maximum) Variations Figure 7.20: Pre- Monsoon Temperature Variability from 1981-2010. 7.21 Pre-monsoon Temperature (Maximum) Variations
Figure 7.21: Pre- Monsoon Temperature Variability from 1981-2010.
7.22 Monsoon Temperature (Maximum) Variations Figure 7.22: Monsoon Temperature Variability of Dhaka City from 1981-2010.
So, it is observed that the temperature (maximum) is increasing and the minimum temperature is also decreasing in trend. About 3.1°c temperature increased from 1981-2010 and 0.4°c temperature fall within this time. It is also remarkable that the urbanization factors such as industrialization, developing of built up areas, extensive land filling, clearing forest and vegetation cover, destroying cultivated land, burning fuel from brick kline’s and unplanned housing are responsible for this drastic increment of temperature. The increasing population is the vital cause of rising temperature. Over the decade the population growth reached beyond to the ‘carrying capacity’ of the city. Again the transportation sectors contributing highly to the rising temperature of the urban area. 7.23 Humidity Variations (Monthly) Table 7.23: Monthly Humidity variation from 1981-2011.
7.24 Humidity and Climate Change Humidity is another important ingredient of climate. The amount of humidity depends on the availability of moisture in the upper air. The higher the vegetation cover and agricultural field, the amount of humidity would be high. Other than if these cover change than it will impact the content of relative humidity in the air. March and April are the least humid months of country. The lowest average relative humidity (57%) recorded in the month of March. The average relative humidity for the whole year ranges from 78.1% -70.5% throughout the country. In Dhaka, the average relative humidity in winter season is 67.3% where February is the lowest humid month. Again, in pre-monsoon time, the average relative humidity varies from 61.5-80.2% where as the relative humidity of the monsoon season varies from 75-85.6% (Figure 7.23). There is an important thing to notice that the average relative humidity shows highly variation. It is clear that climate is changing from the historical time period. The Dhaka city is also contributing in the climate change by emitting various heating elements. Though, the concentration is very low. However, land uses change contributing to this climate change extensively. 7.25 Role of Urban Vegetation in Climate Variation ( Uttara and Ramna):
Ramna is the core environment saving region in Dhaka city. It plays a great role to absorb excessive heat produced by the urban dwellers. It may perceive during the pahela Boishakh and various others occasion in Dhaka city. It is observed the ramna and uttara green areas moderately tempered in comparison to other places of the Dhaka city. Moreover, it also helps to protect the city from being heating due to â€œ Urban Heat Islandâ€?. 7.25.1 Direct economic benefits of urban forests In Bangladesh though budget incurred on the urban forests is tensed to negligible, nevertheless if they can prove their cost-effectiveness their sustainability could draw the kind attention of the policy makers. Though some residents wonder whether it is worth the trouble of maintaining street trees in front of their home or in their yard. Certain species are particularly bothersome due to litterfall, roots that invade sewers or heave sidewalks, shade that kills grass or exudates that foul cars and other objects. Branches broken by wind property, Thorns and low-hanging branches can be injurious. These problems are magnified when trees do not receive regular care, or when the wrong tree was selected for planting. So for our better understanding of the values of urban forest, we can seek the answer of the following question: 1. Are trees worth it? Do their benefits exceed their costs? If so, by how much? 2. In what locations do trees provide the greatest net benefits? 3. How many years does it take before newly planted trees produce net benefits in Dhaka? 4. What tree-planting and management strategies will increase net benefits derived from Dhaka urban forest? A Benefit-cost analysis could be used to answer the aforesaid questions. But due to the unavailability of relevant data it was not possible to assess their benefits (McPherson et al.1997). Most literature available on urban forestry concerns trees, rather than the people who might benefit from them. There is a particular dearth of published information about the relationship of Third World urban dwellers (particularly the poor) to urban trees and forests; on whether or not they value, use, or would like to use trees; and how urban trees affect their health and well-being(Carter 1993). But from a simplified view we can easily understand the worth of urban forest especially of most densely populated and highly polluted Dhaka city. 7.25.2 Urban Forestry for maintenance of wholesome environment
The urban environment is very much different from the rural or countryside environment. Cities are characterized by predominance of concrete structures such as buildings, road, post and also stone, asphalt and metal. These metals absorb and radiate heat easily. The materials have also high reflective power for light and sound (Olembo and Rham 1987). On the top of these, metabolic and industrial activities in the cities produce a great amount of heat and dust. The air thus becomes filled with carbon dioxide, carbon monoxide, sulphur dioxide and many other pollutants and dust. As a result, the climate of a large city is affected adversely resulting in higher temperature and lower humidity. The sunlight is often partially covered by haze, smoke or even fog induced by emissions. If the situations of the cities of six municipal corporations such as Dhaka, Chittagong, Rajshahi, Khulna, Sylhet and Barisal are compared with those of rural areas, a significant difference in respect of temperature, humidity and cleanliness of the air will be observed. The reason is obvious. Apart from the absence of pollutants, the trees around the homesteads and farmlands exert positive effects in ameliorating the wholesome environment. (Zabala 1991) The major urban centers in the country are the metropolitan cities of Dhaka, Rajshahi, Khulna and Chittagong. Dhaka is one of the most densely populated cities in the world. 7.26 Annotations
Based on the results of the above study, the following conclusions are made: 1. The urban land cover is changing rapidly as 55.8% of land turned into built up area from 19602010. That has been done by destroying wetlands (22.21%), waterbodies (0.6%), vegetation cover (4.4%) and agricultural lands ( 20.16%) etc.The land filling activities have increased( 6.6%) significantly.This activities are happening at the cost of wetlands and agricultural lands. 2. In future, about 66.3% land will be converted into built up area where as water body (15.2%) , vegetation cover (3.6%) and agricultural lands (16.59%) will be decreased enormously. The security of urban food and water will be hindered to support the growing population. 3. The vulnerability of urban flooding will increase as 236.87 km² still remain at the moderate to very high flood hazard zones. Of them, 85.96 km² area is highly vulnerable, where about 1.1 million people reside 4.The people’s exposure to the flood hazard due to perennial flooding is more hazardous than natural flooding. People’s exposure to this perennial flooding is 37.5% where as 39.92% was in the natural flooding year of 1998. 5. The urban minimum temperature has slightly decreased (0.4˚c) where as maximum temperature increased ( 3.1˚c) from 1981-2010. The rural-urban maximum temperature variation is high in range (31.6˚c to 39.6˚c).This phenomena support the urban heating as well as global warming.
6. The rainfall, evaporation and humidity conditions are highly variable in Dhaka Metropolitan Area. The average annual rainfall ( 2147mm) remains same but ‘the months without rainfall’ is increasing. About 54 months didn’t experinces rainfall from 1981-2010. 7. The rate of evaporation is decreasing (1120mm -950mm) and the percentage of relative humidity also decreasing (85.6%-67.3%) from the average of 75.6%. This is the clear impact of landuse change.
8. LIMITATIONS OF THE STUDY
The study has been conducted under the several constraints particularly the following things were very crucial. The limitations are-
The study was carried out by using 90 m SRTM data. More précised data can
show better result.
The study considers the Ramna and Uttara area due to the paucity of
available time their costing.
Due to time constrain, analysis of vegetation coverage by using GIS and RS
were done hastily.
Land use classification was done soundly but quandary is remaining as
Only 30 years of climate data were collected to firm the impact climate and
land use change relation which is very diminutive step in terms Geological time Scale.
9. CONCLUSIONS We need to plan for our city and make it a better environment to live in. Whatever determines the fortune of our environment determines also the fortune of our people. We have the power to change our world and everything we do, say and think shapes our reality. Saving the environment is a vital task for all of us. Pollution is increasing in the cities of Bangladesh in spite of government regulations to control it. Parks, squares, street trees, and other greenery and open space in are vital assets of a healthy and livable city. The ecological benefits of these resources are substantial: landscape improves air quality and lowers dust levels, provides vital habitat and corridors for birds and wildlife, reduces water run-off and erosion, and allows groundwater recharge. Trees and other plants absorb carbon dioxide and thus lower the city's contribution to global warming, an important capacity since the phenomenon of global warming has recently passed from theory to confirmed reality. Urban forestry may be practiced to redress the adverse effects of pollution and thus ameliorate the environment. Trees reduce air pollution by filtering air through leaves by the process of sedimentation. Gaseous pollutants and unpleasant odor are reduced either by absorption or masking them with pleasant foliage and floral fragrance. Vehicular noise is also absorbed by the leaves and trees can reduce sound pollution. The vegetation can also provide comfort to the city dwellers by improving the climate like temperature, humidity and air movement. In the wealthier developed countries, urban forestry focuses on amenities and environmental benefits. In poorer countries urban forestry must first pay attention on assisting in fulfilling basic necessities. Much more study is needed to quantify the benefits of urban and peri-urban forestry, to understand the dynamics of demand and flows of forest and tree resources between the rural and urban areas, and to develop a scientific knowledge base for urban forestry. 10. RECOMMENDATION Human and Natural forces can change urban forestry in our country as well as Dhaka city. By understanding how human and natural forces interact within urban systems to create change, management can minimize negative forest changes and facilitate positive changes. Human forces (e.g. urban resident involvement in tree planting, maintenance, and management) and Natural forces (e.g. Extreme temperature events, Fire). Human activities not only change urban forest structure to meet design and functional needs but also try to minimize and prevent detrimental changes due to natural forces (for example, controlling
insects and diseases or altering structure.) to sustain desired forest structure. A combination of human actions and natural forces will continue to shape the urban forests in the years ahead. To facilitate comprehensive and adaptive management to sustain the entire urban forest ecosystem, the following topic areas need to be emphasized: •
Improving inventory and assessment
Improving dialogue among owners, managers, and users
Improving the understanding of how forest configurations influence forest use
and benefits •
Increasing knowledge about factors that influence urban forest health
Improving the dissemination of information about urban forests and their
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Published on Sep 28, 2013
Dhaka is one of the fastest growing urban areas in the world and largest city in Bangladesh. It has a population about 9 million within DCC...