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Drought is a natural phenomenon that has significant economic, social, and environmental impacts. Drought differs from other natural hazards in that its onset and end are difficult to determine. It develops slowly, and its impacts may remain for years after termination of the event. No single definition of drought exists that applies to all circumstances, but most definitions of drought are based on an expression of deficiency of precipitation resulting in water shortage for some activity related to use of water (Wilhite and Glantz, 1985; Dracup et al., 1980). Water resources planners usually rely on quantitative indices to decide whether or not a drought exists. Consequences of drought are usually defined by the impacts that human use systems place on water supply. Drought impacts are usually first apparent in agriculture but gradually move to other water-dependent sectors. Recovery time for water stored in surface and subsurface systems can be quite long under severe drought conditions.
Risk of drought is still a major concern in parts of Turkey where precipitation amounts are low and extremely variable. The combination of rainfall deficiency and other climatic factors, especially high temperature, creates a serious risk of drought in the central and southeastern parts of the country, where agriculture is the main economic sector (Komuscu, 1998). The impacts of drought in the low and variable rainfall regions of the country can be widespread, affecting such diverse sectors as agriculture, irrigation, and energy. In particular, the southeastern Anatolian region, which is the host of the Southeastern Anatolian Project (GAP), may face a serious threat from persisting drought conditions. Moreover, the project includes large-scale irrigation, which stimulates higher competition among the water-dependent sectors.