A Preliminary Study on the Precipitation Variation of Complex Watershed on Forestry and Grasses of Qilian Mountains

In this paper,the precipitation variation was preliminarily studied in the Pailugou complex watershed on forest and grasses,which located in the Xishui research areas of Qilianshan Mountains.The results showed:(1)The precipitation in watershed had obvious seasonal change,plentiful in summer and autumn and rare in winter and spring;(2)The variation of precipitation was a result of comprehensive effects of atmospheric circulation and local micro-climatic and environmental factors.The local micro-climatic and environmental factors could probably more or less influence the precipitation.A markedly correlated linear regression relationship existed among the monthly precipitation(R,mm),vapor pressure(P,Pha),air temperature(T,℃),air humidity(W,%) and evaporation(E,mm): R =-98.206 3 + 11.735 3 P + 1.135 0 W + 0.086 1 E-2.294 6 T,the correlation coefficient is 0.948 6;(3)The point precipitation increased with elevation in certain range.In the elevation of 2 600~3 300 m the precipitation increase rate per 100 meter in elevation was 4.95% in average.The annual precipitation declined with elevation hoisting when the elevation was over 3 300 m or closing the peak.Precipitation varied dependent on slope direction(or vegetation type) besides altitude,and the precipitation in shady slopes was about 7% higher than that in sunny slopes in the studied watershed.Difference vegetation type with same elevation and slope direction would not arouse precipitation discrepancy;⑷The watershed average time or annual precipitation could be comparatively accurately calculated from the measured time or annual precipitation in the climate station located near the watershed outlet with the mode Ⅱ.