The Temporal And Spatial Distribution Of Precipitation Over Yangtze River Catchment From 1952 To 2007

The global warming has become hotspot topic within scientific community and also the great concern for our societal development. IPCC (the 4th assessment report, 2007) has confirmed global warming by referring to data of ground temperature, sea-level altitude, and snow cover area, etc. And it also pointed out the global warming had impacted on the redistribution of precipitation. Meanwhile, the Yangtze River basin suffers from sever floods and droughts in the recent decades, which poses a great threat to our country. Therefore, this paper discusses the redistribution of precipitation over the Yangtze River catchment in the past 56 years, in order to reveal the role of precipitation as controlled by adjusted air-circulation in response to the global warming.This paper has carried out the analyses on the time series trend and the abrupt time change of precipitation over the 46 observing stations in the Yangtze River basin. The entire Yangtze basin can be divided into the eastern Tibetan Plateau monsoon area, Si-Chuan basin, southwestern monsoon area, and mid-lower Yangtze basin. Our analyses of precipitation data were conducted based on different time scales, including annual, four seasons, and June, July, and August from 1952 to 2007, by using the Mann-Kendall method. The results are showned as below:1) Dramatic reduction in annual precipitation occurs over the Sichuan Basin and the southwest monsoon climatic region, while slight increase happens over the eastern plateau monsoon region. There is little change over the mid-lower Yangtze basin.2) Precipitation in spring slightly increases over the eastern Tibaten plateau while remarkable reduction occurs over the Sichuan Basin, the southwest monsoon climatic region and the mid-lower Yangtze basin.3) Precipitation in summer shows an increasing trend in general over the whole Yangtze River basin during the past 56 years, but a decreasing trend is detected over the Sichuan Basin and in the central-western part of the southwest monsoon climatic region. 4) Precipitation in autumn shows a dramatic reduction over the whole Yangtze River basin, especially over the Sichuan Basin and the southwest monsoon climatic region.5) Precipitation in winter shows an increasing tendency over the Yangtze River catchment, mostly over the eastern Sichuan Basin and the mid-lower Yangtze basin.6) Analysis of precipitation during the flood season from June to August shows that the change in August differs from June and July obviously. The number of stations with decreasing tendency appears to be more than that of increasing tendency, that is to say that only the mid-lower Yangtze basin presents the growing tendency in August.7) Abrupt changes generally occur in precipitation over the Yangtze catchment during the period from later 1980s to 1990s. Spatial distribution of precipitation over the Yangtze River basin has changed significantly since 1990, characterized by the shrinking rainfall areas both over Dongting Lake and Poyang Lake in April and May and over the Sichuan Basin in July. The rainfall center over the northeastern Sichuan has almost disappeared, but precipitation over the mid-lower Yangtze basin increases remarkably in July.Author suggests that the temporal and spatial redistribution of precipitation over the Yangtze River basin in the past 56 years can be regarded as the regional response to the global warming. In the recent decades, the ground temperature of the eastern and western China has been rising, along with continuous rising in sea surface temperature in China offshore; besides, the heating source effect of the Tibetan plateau is waning down. All these facts have resulted in the redistribution of seasonal ocean-land temperature differences, leading to the weakening of monsoon circulation in the East and South Asia. Weakening of monsoon activities has resulted in the reduction of spring precipitation over the Yangtze basin, and the waning rainfall belt center of Dongting Lake and the Poyang Lake. During summer, water vapor from the Western Pacific, the Bay of Bengal, and the South China Sea can hardly penetrate into the western and the northern Yangtze River basin, leading to remarkable reduction in precipitation over the central & western areas of the Sichuan Basin. Meanwhile, stagnant rainfall belt occurs in the mid-lower Yangtze basin, which has led to frequent floodings in the recent time.