IPCC Third Assessment Report suggests that eastern and central European countries could become highly vulnerable to global warming. Our investigations support these findings, especially, in case of two subregions: (1) Hungarian Great Plain, (2) watershed of the Lake Balaton. Severe shortage of precipitation occured in the last few decades in both areas, therefore, ecosystems must face to high risk of environmental change. The Great Plain is the largest agricultural area in Hungary where high variability of floods and droughts cause severe damages in crop yields and human settlements, as well. Although the recent mean precipitation decrease is small and not significant, frequent extreme events (e.g., floods with fast runoff) may result in unstable climate conditions and increased vulnerability of agricultural activity in this region of the country. The largest lake in Western and Central Europe is the Lake Balaton with its unique 3.3 meter depth on average. In the last few years, the mean water level has decreased by 60-80 cm several times for a few months period. The only outflow of the lake, a small creek (called Sio) has been regulated and a sluice system has been built in 1863 in order to control the water runoff from the lake to the river Danube (120 km distance). Nowadays ships cannot use the channel because of the recent low water level, and the sluice system must have been closed for years.

These facts highlight the importance of hydrological and agricultural planning, and encouraged our research. The aim of our investigations is to compare climate change scenarios for these two sensitive regions. Several downscaling techniques have been compared, namely, (1) stochastical downscaling method nested in coupled ocean-atmosphere GCMs, (2) an upwelling diffusion energy balance model combined with GCM outputs and IPCC emission scenarios. The stochastical downscaling method includes large-scale circulation of the atmosphere, and also, it is able to represent the linkage between the local surface variables and large-scale circulation. Seasonal and annual changes in temperature and precipitation have been determined for Hungarian stations in case of the 2xCO₂ climate and compared to historical time series. Furthermore, several IPCC emission scenarios have been compared and GCM outputs have been analysed in order to project climate conditions (inlcuding daily mean, maximum and minimum temperature, and precipitation) for the 21st century in the Carpathian Basin.