Changing Trend and Features of the Runoff from Mountain Areas of Rivers in Shiyang River Drainage Basin

In this paper,measured data of precipitation,evaporation,temperature and runoff from meteorological and hydrometric stations in the studied basins were used for researching the changing trend and features of the runoff from the mountain areas of some main rivers in the region.The result shows that there is a decreasing trend of mean annual runoff in Shiyang river drainage basin,in easten and middle reaches,there is a decreasing trend,but in weasten reaches is tend to increase.The average distribution of the runoff due to the conditions of supply,the runoff of season in turn for the summer,autumn and spring and winter.There is a decreasing trend in the observations on runoff in four seasons,most significant decreases occur in summer,the least in winter;It is also found that the vibration periods of 6~7 a,9~10 a long period and 2~3 a short period are displayed very clear in Shiyang river drainage basin.The probability of mean water is the biggest in different age in Shiyang river drainage basin.On the attribution,we calculated the correlation coefficients of climate factors with runoff,positive correlation between runoff and regional precipitation is significant,and negative correlation between runoff and regional evaporation is also significant,indicating that the variations of regional precipitation and evaporation have predominant effect on the runoff variations,and maximum temperature is important factor.And the regional mean and minimum temperature also have different influences on the runoff variations.Synthetic effect of regional climatic elements is the prime cause for runoff variations in the source region of the Shiyang river drainage basin.