Abstract:

Zhelin reservoir has large area and storage,but its catchment area is relatively small.Main constraining factor is deficient water resource.Research of the wet and dry climate conditions and its trend of upstream area in the last 50 years is very important to make effectiveness and scientific investment plan for Zhelin reservoir.Different time scales of standardized precipitation index(SPI index)were calculated by using daytoday precipitation,temperature and other observations data of three conventional meteorological stations in upstream area of Zhelin reservoir from 1958 to 2007.Using SPI index,dry and wet conditions of river basin were studied.Based on FAO PenmanMonteith method,evapotranspiration was calculated.Margin of annual precipitation and evapotranspiration was on behalf of approximate maximum depth of runoff.Linear trend fitting,moving average,and other analytical methods were used to analyze droughts and floods,evapotranspiration,maximum depth of runoff time distribution,seasonal changes,trends and so on.The results show that on the upstream area of the Zhelin reservoir basin,annual precipitation had a significant downward trend,but evapotranspiration had a upward trend since 1998,which led to maximum depth of runoff obvious declining and reservoir water resource being shortage.In the last 50 years,the precipitation concentration showed an upward trend in the river basin.The contribution to the total precipitation of heavy rainfall was increased.The risk of droughts and floods was increased.Droughts and floods appeared alternately in the last 50 years.The frequence of droughts was higher than floods.