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Future development of water related extremes and water stress: A global assessment

Congress: 2008
Author(s): Lucas Menzel, Frank Voss, Martina Floerke, Joseph Alcamo
Center for Environmental Systems Research (CESR), University of Kassel, Kurt-Wolters-Str. 3, 34125 Kassel, Germany

Keyword(s): water stress, hydrological extremes, scenarios, global, WaterGAP
AbstractThere is no doubt that social and economic development will lead to higher future water demands. Consequently, water stress will further increase in many regions on Earth. Climate change will enforce this process through its impacts on both water availability and human water demand, a situation exacerbated by the requirement to maintain river flows for environmental needs and services. The described developments require an assessment tool which combines both the simulation of water availability and its dependency on climatic conditions as well as the modelling of water use impaired by climatic, social and economic development. For this purpose we develop and apply the global water model WaterGAP. It consists of both a hydrology and a water use component. The latter includes a series of modules which simulate water use in households as well as in the industry and agricultural sectors. They take into account the most important drivers for water use intensity, such as climate conditions, population development, economic and technological change, irrigated area, livestock density etc. WaterGAP calculations cover the entire land surface of the globe which is divided into a 0.5 model grid. In this study we address global change and water related issues based on the scenarios and driving forces developed for the latest Global Environment Outlook (GEO) project, launched by UNEP.GEO aims at providing comprehensive, scientifically credible and policy-relevant assessments on the interaction between environment and society. CESR is contributing to GEO by designing and modelling future water related scenarios. The following assessments have been generated by the use of WaterGAP: data on people and area suffering from severe water stress (i.e., the ratio between water availability and water withdrawals), change in runoff extremes, and discharge of treated and untreated wastewater. This was carried out for a total of four different GEO scenarios. They share the common time horizon around the year 2030 but include different policy approaches regarding the management of future challenges. The range of policy initiatives covered by the four scenarios will have different effects on the occurrence of water stress. The results indicate however that growing populations and the increase in economic activity lead to an increased demand for freshwater in most scenarios. The number of people living in areas with severe water stress will therefore increase in nearly all parts of the world, especially in large regions of Asia, Africa and South America. This is partly due to further population growth in already water- stressed areas and partly due to new areas experiencing severe water stress. In other regions (e.g. Northern Europe and North America), elevated precipitation totals and reduced water withdrawals will lead to increased water availability and decreased water stress. According to the scenario assumptions, there will also be increases in the occurrence of runoff extremes. More dry extremes occur in regions with decreasing precipitation totals accompanied with an increase in the coefficient of variation for runoff (e.g. large areas in the Mediterranean and Northern Africa, Southern Africa, Asia, Australia and South America).
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