Climate Change And Response Of Surface Runoff In Bosten Lake Watershed, Xinjiang

Climate change has drawn great public attention in the world. With the trend of global warming, Bosten Lake Basin, located in the arid inland area, has changed from the condition from warm-dry to warm-wet, which has brought a series of impacts on the surface water resources.This article focuses on the climate change and its effects on runoff in Bosten Lake watershed from1961to2008.The daily temperature and precipitation data from ten meteorological stations and the hydrological data of two representative hydrological stations at Kaidu River(Dashankou station and the Yanqi station) was analyzed in order to study their interdecadal, inter-annual and intra-annual statistical characteristics, linear and nonlinear trends, mutation point and continuous characteristics, on which we can try to investigate the main influencing factors of runoff and analyze its response to climate at different scales. The conclusions are as follows:The temperature in Bosten Lake watershed shows upward trend, the temperature anomaly percentage of the most ones in10stations are negative during1960s to1980s, and positive after1990s. The annual average temperature are vary from-4.26℃to14.26℃,and the change rates are0.26℃to0.45℃/10a,which is higher than that of Xinjiang province(0.22℃/10a).The temperature change tendencies are alike among the10stations, which all changed from cold to warm, and the catastrophe points happened in around1990s. The Hurst index indicated that current temperature change tendency will be continuous in the future. There are24-year cycles for the temperature of most stations. The warming trend of each season is significant, and the rate is in the order of winter> spring>summer>autumn, with the largest rate is0.46℃/10a in winter. The interdecadal change tendencies of precipitation data from each station is alike, which is rising obviously and most of the interdecadal means is negative before1980, and positive after that year. The average annual rainfalls and change rates over the study period are different, the former vary from14.22mm to266.55mm, and the latter from1mm/10a to55.07mm/10a. There are precipitation mutations for five stations during1970s to1980s.The precipitation mean of ten stations has a25-year cycle, but the cycle of each one is not completely the same. According to the Hurst index, the precipitation will continue to increase in the future. The seasonal distribution of precipitation is uneven, concentrated mostly in summer (67.44%), spring and autumn take about the same amount, and winter is the last. Each season shows an upward trend, with the change rate in a rank order of summer> spring> autumn> winter, and the summer precipitation increases at8.19mm/10a, which made the greatest contribution to annual precipitation change. Before1990s, the runoff anomaly percentages of the two hydrological stations are negative and positive after that. The annual means for many years are35.04*108m3,25.49*108m3,and increases at the rate of2.02*108m3/10a,1.94*108m3/10a.There are obvious nonlinear trends at different time scales. In32(25)year, the runoff of two stations present an obvious ascending tendency, in16(24)year and8(23)year, they take on the rising trend with the fluctuation, and in4(2)year, the curves appear four fluctuation periods, with cycle of about10years, which is very close to that of the temperature and precipitation in the area. The catastrophe points of runoff of two stations happened in1996and1997from low to high, and the current flow will continue to rise in the future. Periodic analysis confirms that the runoff have a24-year cycle, which is closed to that of average temperature and precipitation from ten stations. The seasonal distribution of runoff is uneven, which is higher in summer and lower in winter, the spring and the autumn have similar proportion.The runoff of Dashankou station is changing under the combined influence of temperature and precipitation, and the impact of the latter is larger than the former, runoff is mainly related to precipitation in summer and temperature in winter. From2year to32year scale, the impacts of Climate factors are more and more remarkable. Compared with climate factors, Yanqi station has the highest relationship(-0.64) with artificial exploited water quantity in Yanqi Basin, then the precipitation in the upstream, at last the temperature in Yanqi station. In2year,4year,8year,16year and32year scale, the runoff have positive correlation coefficients with the precipitation and temperature, and inverse correlation with artificial exploited water quantity. As the amplify of time scales.the sensitiveness of the runoff enhances to the precipation upstream,and reduces to the temperature upstream and nearby.At different scales, the response of runoff to different factors is different, at the smaller time scales, the response to precipitation is more obvious than to temperature. As the amplify of the time scales, the response to temperature is more and more prominent, and influence of human is very significant with the runoff at all scales.