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The world’s global population has crossed the 7 billion people threshold, and this has triggered much debate regarding resource availability to accommodate such increasing human numbers. An objective appraisal of the scientific knowledge pertaining to the current and future state of global water resources has been undertaken to discern the certainty with which we identify areas of evolving water stress and how such knowledge is applied by users. Through a selection of country-level case

What constitutes water st security in the 21 Century? The challenge of synthesising hydrological and socio-economic knowledge within the uncertainty surrounding climate change The world’s global population has crossed the 7 billion people threshold and continues to rise, as have resource requirements. This has triggered much debate regarding resource availability to accommodate such increasing human numbers and continued economic growth. The added pressure of climate change and potential perturbations to the global hydrological cycle further complicates our ability to plan for and implement adaptive measures to ensure water security. An objective appraisal of the scientific knowledge pertaining to the current and future state of global water resources has been undertaken to discern the certainty with which we identify areas of evolving water stress and how readily such knowledge can be applied by stakeholders. The data and tools Spatial scale - national/regional/basin/gridded/city/water resource zone Temporal scale – yearly average/minimum/season/monthly/drought/flood/present/future Data on water use and consumption- national/institutional/private enterprise/modelled Meteorological and hydrological data – precipitation/temperature/evaporation/land use/soil/crop types Hydrological model s and water distribution models – land surface/rainfall runoff/water budget/water distribution Vast array s of global data required to assess MDG and WWDR indicators Water in the environment Surface water – rivers, lakes, reservoirs, glacier melt Groundwater - fossilised or renewable Polluted water – arsenic, nitrates, diffuse, point Green / Blue water concepts Consumptive use or loss from systems Water footprint and trading of virtual water in products Who is concerned and why? Government – ensuring water security Water companies and regulators – meet demands and manage supplies to mitigate low input and future supply demand International policy maker – maintain global development NGO – access to water supply Industry – water security for business development Consumer – hosepipe bans and bills Farmer – crop requirements Scientist –climate change and environmental impacts

Source: International Water Management Institute

How can we define water stress and water security – what must we consider? Management and socio-economic factors Water technology – reservoirs, treatment, infrastructure, water efficiency Institutional management – water companies, regulatory bodies Access to sanitation and safe supply Per capita consumption Education

Source: ROCKSTROM, J., FALKENMARK, M., KARLBERG, L., HOFF, H., ROST, S. & GERTEN, D. 2009. Future water availability for global food production: The potential of green water for increasing resilience to global change. Water Resources Research, 45.

Some of the vast array of indictors* Drought – severity, frequency River flows – Q95, MAR, TAWR, % change Precipitation – percentage decrease Water company – deployable output Falkenmark indicator Human water requirements and MDG Watershed sustainability index Water supply stress index Physical and economic water scarcity Water Stress Indicator Water Resources Vulnerability Index Water Footprinting Water Poverty Index Adjusted Human Water Security * The World Water Development Report 4 (2012) reports that over 160 indicators were reported in the first edition of the WWDR to monitor the state, sue and management of water resources for a wide variety of purposes, and this has reduced to 49 for the most recent assessment

Environmental security Environmental flow requirements Habitat loss Aquatic species, terrestrial species, migratory species Water pollution - arsenic, nitrates, diffuse, point and impacts on ecology Regulations – WFD, RAMSAR,

Source: Sullivan, C.A., Meigh J.R. and Fediw T (2002) Developing and testing the Water Poverty Index: Phase 1 Final Technical Report. Report to Department for International Development, CEH Wallingford

Source: Vörösmarty, CJ, McIntyre, PB, Gessner, MO, Dudgeon, D, Prusevich, A, Green, P, Glidden, S, Bunn, SE, Sullivan, CA, Reidy Liermann, C & Davies, PM 2010, 'Global threats to human water security and river biodiversity', Nature, vol. 467, no, 7315, pp. 555-561

Add climate change to this complex array of factors that compound uncertainty when considering water stress and the task for a policy maker or scientist in providing a clear statement of change is challenging. •Uncertainty of GCM projections based upon variable future emissions scenarios • Natural variability of systems and inter annual variability •Climate model uncertainty in changing precipitation and temperature •Uncertainty in how global scale models provide accurate downscaling •What impact will these changes have on water supply and demand

Our best guess – how confident can we be about the future? What does a synthesis of the available evidence reveal? Recently published work in collaboration with the Met Office Hadley Centre and the AVOID team (http://www.metoffice.gov.uk/climate-change/policy-relevant/obs-projections-impacts ) conducted a review of all post AR4 science on the subject of water stress and drought for 24 countries. Some of the key conclusions are listed below and highlight the difficulty in providing a simple definitive assessment of climate change impacts on water security and the uncertain language that results from combining variable models, indicators and climate change uncertainty.

United Kingdom – National scale studies mask water stress on the south and east of the UK where droughts are expected to increase while the rest of the UK may be relatively unaffected. Median AVOID results from 21 climate models suggest no increase in UK water stress as a whole. Australia – A high degree of uncertainty in how climate change will affect water availability and a wide array of indicators of water stress applied makes corroboration of impacts difficult. AVOID results differ from existing literature and indicate no change in water stress. India – A consensus that water stress could increase but the magnitude is uncertain due to wide-ranging estimates from climate change projections. Why should we continue to work together to distil current knowledge into fewer, simpler, universal water indicators that can consider future uncertainty?

Because effective adaptation and communication to ensure water security requires consistent, transparent and readily interpreted indicators.

James Miller – millj@ceh.ac.uk

The challenge of synthesising hydrological and socio-economic knowledge  

James Miller, Centre for Ecology & Hydrology, UK--- The challenge of synthesising hydrological and socio-economic knowledge within the uncer...

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