Study for Separating the Impact of Precipitation Variation and Human Activities on Runoff Change of the Upper Reaches of Jing River

This paper analyzed the characteristics of climate and runoff of Jing river upstream in the past 52 years(1954-2005) based on the measured data of climate and the hydrological data at Jingchuan station which is the main controlling station on the upstream.The research fund that the runoff series showed a significantly downward tendency while the precipitation was even and pan evaporation had weak downtrend,indicating that the down trend of runoff was caused by human activities.The double mass curve method were used to detect the abrupt change and made off four stages: 1954-1960,1961-1971,1972-1980,1981-1997,1998-2005.We obtained a regression equation based on the data of precipitation and runoff in 1954-1960.Using this equation the impact of human activities increasing on runoff can be quantified after 1960.The calculated results showed that except that low precipitation was the main reason leading to runoff reducing in period 1991-1997,human activity was the more important reason that impacted the runoff variation in other periods.For example,human induced runoff increasing were 52.71,9.22,3.42 mm in three periods 1961-1971,1972-1980 and 1981-1990 respectively,but precipitation induced runoff increasing was 5.38 mm only in the period 1961-1971 and runoff decreasing were 2.85 mm,2.93 mm in other period 1972-1980 and 1981-1990 respectively;In addition,compared to precipitation that induced runoff increasing 1.73 mm,human activities induced runoff decreasing were 24.87 mm in the period 1998-2005.Finally,we discussed that further quantitative distinguish the contribution of climate warm and specific human activity on variation of evapotranspiration and runoff was the research requirement.