Projection and Possible Causes of Summer Precipitation in Eastern China Using Self-Organizing Maps

Self-organizing map (SOM) is used to simulate summer daily precipitation over the Yangtze-Huaihe river basin in Eastern China, including future projection. SOM shows good behaviors in terms of probability distribution of daily rainfall and spatial distribution of rainfall indices, as well as consistency of multi-model simulations. Under RCP4.5 Scenario, daily rainfall at most sites (70%) is projected to shift towards larger values. For the early 21^st century (2016-2035), precipitation in the central basin increases, yet significant decreases occur over the middle reaches of the Yangtze River as well as a part of the southeast area. For the middle horizon (2046-2065), the area of rising precipitation expands to the middle Yangtze River. As to the last stage (2081-2100), the mean and extreme precipitations experience an overall increase. Moreover, the total precipitation in the lower reaches of the Yangtze River and south of it may increase from 8% at 1.5°C global warming to 15% at 2°C, while the intensity enhancement is more significant in the middle reaches of the Yangtze River. A clustering is furthermore performed to regroup all SOM nodes into four distinct regimes. The regional synoptic regimes show a remarkable stability for future climate. The overall intensification of precipitation in future climate is linked to the occurrence-frequency rise of a wet regime which brings closer the South Asia High and the westward Western Pacific Subtropical High, as well as the reduction of a dry pattern which makes the two atmospheric centers of action go away from each other.