The annual variation changes of the drought and flood in summer of southwest region

摘要

This paper uses monthly precipitation data of the 46 stations from 1951–2007 in southwest China, classifies and analyzes the average distribution of the climatic precipitation in summer and the distribution of the yearly anomaly field in southwest region, then does EOF analysis for the exceptional field of summer average precipitation in southwest region. The results of the climatic analysis show: the character of the summer average precipitation is ladder-like distribution in China, and it decreases from southeast to northwest, while the precipitation is the largest in central Sichuan within the precipitation trend in southwest region, the precipitation of this region is mainly annularity distribution. We can know according to the classification analysis: the character of exceptional field distribution of the yearly summer average precipitation in southwest region can be divided four types, south to north, east to west, southeast to northwest, southwest to northeast. It shows according to the EOF analysis of the summer average exceptional field in southwest region: the first eigenvector annual average summer precipitation anomalies in distribution can be basically divided into the north-south negative positive and negative, positive and negative things to positive, positive and negative direction is southeast to northwest, southwest to northeast direction is plus or minus 4 Large type. Southwest region in the summer anomaly field of the EOF analysis of the average results show that: both the first eigenvector and the second eigenvector are contrary to the north and south, and the large value of the positive one is zonal distribution, while the high value the third eigenvector is meridional distribution, the high value of the negative one in the first eigenvector is southwest - northeast slope distribution, and the high value of the positive on in the second and the third eigenvector is concentrated. The time coefficients are all positive to negative alterna--tely after 2000, in which the time coefficients of the second eigenvector has a positive to negative cycle with 28 years between 1966 and 1994 while the third eigenvector are all of the time factor for the positive and negative alternately.