Attribution Of Hydrological Trend In Dongting Lake Basin

Climate change is one of the most important environmental issue in theworld, increasing human activities also had a huge impact on watershedhydrologic cycle. It’s necessary to quantitatively study the characteristics andlaw of the water resources evolution and analyze the impact of climate changeand human activities on runoff in Dongting Lake basin, where faces manyextrusive and complex water resources problems (flood and drought disasters).This work is of great significance to sustainable utilization of water resourcesand ecological functions maintenance of Dongting Lake.The essay adopted the linear tendency estimation method, the movingaverage method, Trend-Free Pre-Whitening Mann-Kendall and other methodsare employed to analyze the variation of hydro-meteorological elements inDongting Lake basin. From1960to2010, the annual runoff decreased and waterstage dropped at Chenglingji, and the former variation was caused by the runoffdecrease of three inflows. Compared with the period from1993to2002, theaverage annual runoff and water stage at Chenglingji both dropped significantlyfrom2003to2010. The average annual runoff decreased by59.92billion m3,and58.4%was caused by the runoff decrease of four head streams, whichdecreased by35.04billion m3. The average annual stage dropped0.53m. Bybuilding a linear regression model, the contribution of the variation of thedischarge at Chenglingji and the variation of water stage of Yangtze River to thewater stage decrease can be estimated quantitatively. Results showed that theinfluence quantity were0.26m and0.32m respectively. If the runoff of threeinflows was considered, the hydrological characteristics variation of YangtzeRiver accounted for65%.The essay adopted cluster technique method and Mann-Kendall mutationtesting method to detect the transition point of the runoff series of four headstreams. Considering the important time node in the basin, the essay divided therunoff series into three times stages:1979-1988,1989-2002,2003-2010.Based on coupled water-energy balance relationship, the sensitive coefficient of runoff was derived and had been used to quantitatively analyzethe impact of climate change and human activities on runoff in the four mainrivers in Dongting Lake basin. Results showed that climate change accountedfor120.8%,96.1%,97.8%,453.5%in the first two stages, while humanactivities accounted for-24.5%,2.2%,0.7%,-355.5%. Climate change acounted for206.0%,110.7%,112.6%,100.9%in the last two stages, whilehuman activities accounted for-95.3%,-6.9%,-9.8%,0.6%。GBHM model was built in the Dongting Lake basin in order toquantitatively analyze the impact of climate change on runoff in the four mainrivers. Results showed that climate change accounted for79.6%,69.3%,63.7%,447.2%in the first two stages, while accounted for154.3%,89.7%,107.9%,124.2%in the last two stages.Both the results of two estimating methods showed that climate change isthe dominant factor of the variation of runoff, among it, the variation ofprecipitation plays a major role. Human activities lead to increased runoff inmost of the time, which is influenced by the interactive effects of urbanizationconstruction, soil erosion, soil conservation, reservoir construction, waterconsumption.