ABSTRACT
The long term management and planning of catchments for f lood protection and water resource conservation, agricultural practices (irrigation, crop types and yields), civil and industrial water supply, hydroelectric power, etc. need the accurate knowledge of heavy rainfall and drought regimes which are connected to the climate variability and trends. According to the Third Assessment Report (TAR) of the Intergovernmental Panel on Climate Change (IPCC) (Houghton et al., 2001), the climate system is forced by natural factors (solar energy output, volcanic ash and aerosols, internal dynamics, and feedbacks) and anthropogenic forcings (emission of greenhouse gases and aerosols, land use changes). There is a general understanding and agreement on the sign (positive) of the thermal response of the climate system, the surface, and the atmosphere to the current anthropogenic forcings, although large uncertainties concerning the warming rate remain (e.g. Houghton et al., 2001). The chance of abrupt warming resulting from temporary heat storage in large natural reservoirs, especially the deep oceans (Pielke, 2003), the effects of the land use, vegetation and carbon cycle feedbacks (Jones et al., 2003; Rial et al., 2003), and of the water vapor feedbacks (Del Genio, 2002) are still not completely understood.
