Changes And Probable Causes Of Summer Extreme Precipitation In The Middle And Lower Reaches Of The Yangtze River Under The Background Of Global Warming

In this paper, the temporal and spatial variation characteristics of extreme precipitation in the middle and lower reaches of the Yangtze River were determined by the method of trend coefficient, wavelet analysis and EOF, and found that the intensity and frequency of extreme precipitation in this region showed an upward trend. Again through the synthetic analysis and correlation analysis were analyzed intensity and frequency of abnormal circulation background, and caused a total of extreme precipitation in the region to increase the circulation factor and moisture content, degree of instability, enthalpy change characteristics. The following conclusions are obtained:First, in the middle and lower reaches of the Yangtze River, the annual variation rate of extreme precipitation in summer in most areas of the south of the Yangtze River in the south of 31°N is larger, which is prone to abnormal phenomena. The total amount of extreme precipitation in the middle and lower reaches of the Yangtze River shows an upward trend; the intensity and frequency in most areas of the south of 31°N showed an upward trend, while in the eastern part of Jiangsu and southern Zhejiang there is a small area of decline. Since the 21st century, the Yangtze River on the north side, the Yangtze River to the south area slants little in the middle and lower reaches of the Yangtze River more than heavy rain days mainly for the region’s comments, north-south reverse type; in the middle and lower reaches of the Yangtze River more than heavy rain, the number of modes are quasi Biennial of interannual variation and interdecadal changes, the above heavy rainfall days in the 90s of the 20th century began to increased significantly.Secondly,2000-2011, Eastern by upward still exist "anomalous anticyclonic cyclonic water vapor transport and water vapor transportation in Mongolian Plateau anticyclonic, causing rain stalled in the Yangtze River to the north, resulting in Yangtze River to the South more than heavy rain days less than normal.of the number of South Asia high and the Western Pacific subtropical high strength and position change of summer extreme precipitation intensity in the middle and lower reaches of the Yangtze River, and have significant impact. When South Asia high ridge southerly, strength is too strong, corresponding lower West Pacific subtropical anticyclone westward, southward location of the north and south, the strong side, the regional summer extreme precipitation intensity increases, the frequency increases. North of the South Asia high, strength of the weak, West Pacific subtropical high eastward, the strength of the weak, the regional summer extreme precipitation intensity weakened, frequency decreases. Around the Philippines and the West Pacific region convection anomalies, caused by the wind and zonal wind anomaly, through the influence of the subtropical location, area and intensity and caused East Asian summer monsoon intensity abnormalities induced by to the Rossby wave spread to middle and high latitudes, which leads to the region summer extreme precipitation anomaly.Finally, the change of water vapor content in each layer of the troposphere makes the "upper and lower wet" layer node status more obvious. The increase of the heat content in the middle and lower troposphere provides favorable conditions for the enhancement of the intensity of convective weather. The changes of the two factors are beneficial to the increase of the frequency of extreme precipitation and extreme precipitation in the middle and lower reaches of the Yangtze River, which leads to the increase of the summer precipitation in the region.