Analysis on Water Source Area Precipitation Change of The South-to-North Water Transfer Project Middle Line

The water source area precipitation change of the South-to-North Water Transfer Project middle line directly affect the success or failure of the project.The precipitation data of Yunxi,Shiyan and Xichuan from 1961 to 2008 were selected and analyzed by trend analysis method,cumulative anomaly analysis method and spectrum method.The results showed that during the study period,the overall trend of water source area precipitation was decreasing,but there were significant differences in space.The water source area precipitation was concentrated in summer and had a further centralization trend.The water source area interannual precipitation had obvious stage.There were three obvious increasing periods and two decreasing periods.According to the spectrum analysis,there was a 4-year short period of the water source area precipitation change.