Attribution Analysis On The Change Of Runoff In The Upstream Of Miyun Reservoir During Last30Years

In recent years, the impact of human activity and climate change on waterresources and water environment in North China is increasing. Miyun Reservoiris the most important surface water source forBeijing, having importantstrategic significance for the sustainable development and water security ofBeijing. The upstream of Miyun Reservoir basin is selected as the study area,and the sub-basins controlled by Xiabao, Sandaoying, Zhangjiafen, Daiying andXiahui hydrological station are studied respectively. The changes of runoff ofdifferent levels are analysed under the background of climate change andintense human activities during the last30years. The changes of land use andhydro-meteorological data, furthermore, the inflection years were revealedthrough statistical analysis. Two methods based on improved Budyko Curve areused to quantify the respective contribution of land use and climate changes tostreamflows. SWAT model was used to simulate the water yield and evaluate theimpact of land use and climate change.A statistical model was used to simulatethe flow duration curve and the related model parameters were analysed. Baseflow recession was analysed to understand the storage properties and aquifercharacteristics. The main results are as follows:(1)From1980to2008, the annual runoff reduced significantly and thechange point ofXiahui and Zhang Jiafen occurred in1999. The wet seasonstreamflow decreased significantly. In Xiabao sub-basin, average runoff inOctober was larger than that in flood season. Flow duration curves vary indifferent sub-basins.From1986to2005the main characters of land use changewere the fast increase and subsequent slow decrease of forestland and thegrassland and arable land was from descend to ascend. The fastest changingoccurred from1986to1995. Xiabao sub-basin suffered the most dramaticchanges among all the sub-basins.No significant change happened in annualpotential evapotranspiration and precipitation.(2) Baes on the annual water balance model, climate-elastic method andSWAT simulation results, the contribution of different factors to the runoff decrease were evaluated quantitatively.(3) FDC curves can be simulated well using the4parameter statisticalmodel which was based on the extended Burr XII distribution. The relatedparameters respond to the change of climate and landuse, but it’s hard toquantify the relation.The paramters which reflect the storage properties andaquifer characteristics were computed according to the baseflow recessionanalysis. According to the geohydrologic-geomorphic relationship the parametern was set to2. And the results show that the change of parameter K can reflectthe seasonal change to some extent.