IPCC-AR4 suggests a large precipitation change under the climatic force by increasing green house gases. However, the large model-to-model precipitation deviation between CMIP3 models limits the ability to quantify the regional precipitation or runoff trends. Using a Q-Q technique, we built up a mapping index linking each specific modeled river catchment precipitation and its observational discharge measured close to the mouth. Through those indices, the observational river discharges are well reproduced from the 20th century run (20C3M) model results. Furthermore, with the same indices, we simulate the future 21st century river discharge on Yangtze, Ganges, Brahmaputra, Blue Nile and Murray-Darling River basin under different SRES scenarios.

The Yangtze, Ganges, Brahmaputra River discharges are predicted to have large increase of both mean value and excessive events in the 21st century through the time. In the other hand, modeled Blue Nile and Murray-Darling River discharge present large uncertainty and do not suggest a significant increase or decrease trend from multi-model average.