Regional effects of greenhouse warming on water resources, and more specifically on surface runoff, were assessed for a mountainous region of central Greece comprising four drainage basins by using a conceptual model and plausible hypothetical scenarios of temperature and precipitation change. Results showed considerable sensitivity of runoff characteristics to climate change and indicated certain basin morphoclimatic characteristics such as snow cover, basin aridity and morphology, runoff coefficients etc., which modify considerably basin response.
The sensitivity of some critical water management issues, such as reservoir storage and hydroelectric production, to climatic variability and change on a regional basis was analysed as well. By using a set of plausible hypothetical climatic scenarios to represent both greenhouse warming and precipitation changes, the sensitivity of the guaranteed annual fresh water and energy supply levels has been evaluated under conditions of altered runoff for four connected multipurpose reservoirs in central Greece. It was shown that reservoirs designed and operated under current climatic conditions are, in general, affected by the climatic changes examined. A dramatic increase of the risk associated with the annual guaranteed quantity of water supply and energy production would occur if greenhouse warming was accompanied by a reduction in annual precipitation. Significant increases of storage volume would then be needed to maintain existing water and energy yields at tolerable risk levels.