Estimates of possible regional hydrologic regime changes in the 21st century based on global climate models

Numerical results of global climate models are used to infer possible changes in regional hydrologic cycle characteristics, including precipitation and river runoff, in the 21st century. Both coupled atmosphere-ocean general circulation models and a climatic model of intermediate complexity, forced by scenarios of an anthropogenic increase in the atmospheric greenhouse cyas content, are used. The model results show that the precipitation amounts considerably increase in the high latitudes, in particular, over Eurasia, under anthropogenic warming in the 21st century. This is associated primarily with a large increase in the winter precipitation intensity, especially over northeastern Eurasia. The changes in summer precipitation differ widely, with a large neoative trend occurring in the midlatitudes. This trend is associated with corresponding changes in the probability of wet days. Despite a decline in summer precipitation over a large Eurasian region, the precipitation intensity increases. The relative contribution of intense precipitation to the total precipitation amount increases as well. Model estimates are presented for possible changes occurring in the 21st century in precipitation and river runoff over various regions, including the basins of the Volga, the Caspian Sea, the Neva, Lake Ladoga, the Ob, Yenisei, and Lena rivers. On the whole, the precipitation and runoff in these basins, as well as their variability, are found to generally increase in the 21st century against the background of considerable interannual and interdecadal variability. The average runoffs of the Volga, Ob, Yenisei, and Neva rivers somewhat decline in the first half of the 21st century in the general circulation climate models, whereas no such decline is found for the Lena runoff.