抄録
Simulated daily discharge data derived from a relatively high-resolution (T106) coupled general circulation mode (GCM) were used to investigate changes in the risks of global discharge extremes associated with changes in atmospheric composition caused by anthropogenic factors. The present-day GCM simulation reproduced the magnitude of discharge in 100-year return periods and the global distribution of the flood parameter, even though the absolute value of that parameter was underestimated. The simulated increase in floods and droughts between 2071 and 2100 significantly exceeds the natural change between 1941-2000 and 1971-2000. The frequency of very large floods was projected to increase over many regions, except for continental North America and middle to western Eurasia. Globally, the drought frequency was shown to increase in most regions except over the northern high latitudes, eastern Australia, and eastern Eurasia. Changes in flood and drought are not simply explained by changes in annual precipitation, heavy annual precipitation, annual evapotranspiration, or differences between annual precipitation and annual evapotranspiration. Several regions were projected to have increase in both flood frequency and drought frequency in the future. Such regions include basins in the northern high latitudes, where the timing of snowmelt would be earlier in warmer climates, and basins where precipitation patterns may change so as to decrease precipitation days but increase days with heavy rain. Because the predicted future changes in floods and droughts varied among rivers and sub-basins, projections of disastrous extremes in discharge using high-resolution GCMs will become important for local risk assessment.
