Changes of precipitation and runoff and their causes in the Biliu River reservoir basin

The temporal characteristics of intraannual and interannual precipitation and runoff in the Biliu River reservoir basin were investigated in this study based on daily data from 1958 to 2011.The Gini coefficient method,R/S analysis method and wavelet method were used to explore the intraannual variation.Interannual variation and trend,and periodicity of precipitation and runoff.The results showed that the intraannual distributions of precipitation and runoff in the basin were extremely uneven with a unimodal type.The peak values of monthly precipitation moved backwards after the 1980s.Both annual precipitation and runoff had decreased, and the trend of runoff was more significant than that of precipitation,which implied that runoff was also affected by other factors besides precipitation,such as human activities.Both precipitation and runoff sequences exhibited a cycle of abundance and drought change,and the main cycle was 12-16 years,which might be explained by sunspot cycle activity.The oscillation of runoff cycle was weaker than that of precipitation cycle after 1980s,which indicated that other factors also effected runoff generation besides precipitation.

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