Summer Precipitation Patterns in West China and Its Inter-decadal Changes

Based on the 1961—2000 precipitation observations at 48 selected stations,by using the ISODATA fuzzy cluster method,the summer precipitation in west China is divided into two typical precipitation patterns (characteristic distributions of precipitation).One is characteristic of more precipitation in the most areas of west China and less precipitation in the other areas,and precipitation distributive trends of the other pattern are just opposite to the first pattern.Analyses of the interannual and interdecadal changes of the two precipitation patterns show that the precipitation character in west China has been changed since the mid-1970s.It is also found that the contemporaneous 500hPa circulation and the early time equatorial Pacific SSTA field for the two patterns are remarkably different,which has good indication for the short-range climatic prediction of precipitation in west China.