Abstract: Summer precipitation changes in the middle and lower reaches of the Yangtze River under global were estimated, using the historical simulation of the fifth coupled mode comparison plan (CMIP5) and the experimental data under the high concentration scenario of the typical concentration path (RCP8.5). The results show that the multi-mode average predicted global warming has a small increase in precipitation variation in the middle and lower reaches of the Yangtze River. On the one hand, global warming leads to an increase in water vapor content, which is conducive to the increase of precipitation in the Yangtze River Basin. On the other hand, global warming has caused the Summer monsoon circulation to weaken, and the weakened summer monsoon is not conducive to the increase of precipitation in the Yangtze River basin. Under the combined effect of the two, the multi-model average estimated mid-downstream watershed in the Yangtze River has no obvious changes in summer precipitation. However, there is a large inter-mode uncertainty in this estimate. The analysis shows that the uncertainty of the prediction of precipitation change is mainly due to the uncertainty of precipitation prediction results caused by large-scale Summer monsoon circulation changes, and the increase of water vapor caused by climate warming has less influence on the uncertainty of precipitation variation. Further research on this source of uncertainty shows that precipitation in the middle and lower reaches of the Yangtze River and changes in the East Asian summer monsoon circulation are strongly correlated with the warming of the North Atlantic and the the Western North Pacific SST. This indicates that in the context of global warming, the warming of the North Atlantic and the Western North Pacific SST has a great impact on the prediction of precipitation changes in the middle and lower reaches of the Yangtze River. If the uncertainty of the prediction of the North Atlantic and the Western North Pacific SST is reduced, the precipitation prediction results in the middle and lower reaches of the Yangtze River will be more reliable.

Key words: global warming, middle and lower reaches of the Yangtze River, precipitation, CMIP5