The Elaborate Distribution of Precipitation and Interannual Variation of Total Precipitation in the Upstream of the Heihe River

Using the geographical and topographic data with the resolution of 100 m×100 m and the meteorological observation data including precipitation and wind,in this paper,a new local terrain index of coupling slope,aspect and prevailing wind direction was constructed firstly based on the effect of prevailing wind direction and windward slope on precipitation,proposed by Fu Bayou,and the prevailing wind direction effect index,established by Sun Pengsen.The new index has more clear physical meanings of atmosphere-earth interaction.Then regression equations between precipitation from June to September and geographical and topographic factors were established by means of regression analysis year after year(1967—2008).According to the regression equations,the space elaborate distribution of precipitation from June to September can be obtained by spatial analysis year after year in the upstream.On this basis,the total precipitation can be calculated year after year in this area.The result showed that there were very good correlations between the new local terrain index and precipitation from June to September year after year.Cross test results showed that the regression equations can fit well the upstream precipitation.Especially since the late 1970s,the fitted values have been very close to the measured values.The average relative error was less than 10%.Based on the space elaborate distribution of the precipitation,the mean total precipitation from June to September was calculated to be about 98.2 billion m3 in the upstream of the Heihe River.The total precipitation had obviously interannual variation with a slight rising tendency.Before 1982,the total precipitation showed an ascendant tendency.During 1982 to 2000,the total precipitation fluctuated large.Since 2000,the total precipitation has increased obviously.