Assessing Water Management Challenges and Capacities in African Cities 75
kilometer; and 21 have densities higher than densely populated cities such as Rio de Janeiro (with 5,900 inhabitants per square kilometer) or Beijing (with 4,200 inhabitants per square kilometer). In more than half (17) of the cities, between one-half and three-quarters of the population live in informal areas. In 13 of the 31 cities, less than half the population has access to improved sanitation. This represents a serious social, health, and environmental challenge (Water and Sanitation Program, 2012). In addition, contamination from the informal areas can have a negative health affect for populations in richer parts of the city. In Indore, reducing this health threat was a major driver behind their slum upgrading program (see Chapter 2, Box 2.4). By managing the urban water cycle as a single system, the contamination of water sources by poor sanitation might be lessened.
The Spatial Dimensions of a Growing City Matter to Water Management Rapid urbanization and its spatial dimensions are key drivers of several aspects of the urban water management challenge. However, traditionally, we know little about the location and size of the future development areas. To fill the void, we created maps of past and future urban extent for the 31 selected cities based on satellite imagery and on a methodology for projection of future urban extent.8 This work complements the groundbreaking research by the Lincoln Institute (Angel et al., 2010) that consists of historic maps for 120 cities globally, including 11 cities in Africa. In addition, using a simplified, cellular automata approach based on the Slope, Landuse, Urban Extent, Transportation and Hillshade (SLEUTH) model (Clarke et al., 1997), we developed another set of future extent maps for these 31 cities.9 Future urbanization is described through a four-step process: 1. Define suitability for future urbanization of the areas surrounding the existing city. 2. Exclude certain areas from urbanization (for example, water bodies, national parks, and so on). 3. Determine the size of the future area to be urbanized (in our case by the year 2025). 4. Allocate population growth to highest suitability areas first, then the next suitable, and so on.