Simulation Of The Spatio-temporal Distribution Of Surface Water Resources In Zhangjiakou Section Of Upper Yongding River

The upper reaches of Yongding river(eg.Zhangjiakou C ity)is located in the upper reaches of Beijing and is connected to the capital through the same mountains,rivers and atmospheric environment,and has a special ecological trait.The “Outline of Beijing-Tianjin-Hebei Coordinated Development Plan” lists Zhangjiakou C ity as an ecological conservation area in the northwest,and requires that the outflow of the upper reaches of Yonging river should be gradually increased.However,as a typical arid and semi-arid area,the long-term unreasonable use of water resources has caused a large number of rivers and lakes to dry up in the region.How to rationally allocate and utilize regional water resources to meet both cooperative planning requirements and local development needs is an urgent problem to be solved in the upper reach of of Yongding river region(include Zhangjiakou C ity).To this end,this study attempts to use hydrological models to characterize regional streamflow process and study the distribution of regional surface water resources.The modelling is based on hydrological data and meteriological data at different time periods from 1951 to 2016,the long-term trends of regional hydrometeorological elements were analyzed using Baseflow separation,Mann-Kendall trend test,Double Mass C urves,and Penman-Monteith formula.Based on the Budyko hypothesis,the contribution of climate change and human activities to streamflow changes is quantified.And further discussion about the specific human activities that caused the streamflow decline in the Beijing-Tianjin-Hebei area.Finally,by constructing databases such as soil,land use,and meteorology,the SWAT model is used to simulate streamflow process which based on the distributed parameter calibration and verification.Futhermore,this study taking Zhangjiakou City as an example to reveal the spatial and temporal distribution characteristics of surface water resources in the upper reaches of Yongding river and predict the future regional surface water resources in the context of global change which also provide scientific basis for regional rational use of water resources.The main results presented in this thesis are summarized as follows:(1)Since the 1950 s,the base flow of the upper reaches of the Yo ngding River(including the two major tributaries of the Yang River and Sanggan River)has shown a significant downward trend.The base flow index has increased in most sub-basins,and the contributio n of groundwater to streamflow has increased.The base flow index of the upper reaches of the Ya ng River and Sanggan River is basically smaller than that of the lower reaches,and the streamflow in the upper catchments is more due to rainfall recharge.The streamflow in Upper Yongding River Basin and its subbasins were significantly declining.With relatively steady precipitation and potential evapotranspiration,however,the drought coefficient of each sub-basin has increased significantly,the whole basin showed aridification trend.The streamflow from each basin had the largest elasticity for precipitation,while landscape was the second important parameter,however,the main cause of streamflow variation in upper Yongding Basin was landscape shift caused by human activities,since the 21 st century,the contribution o f human activities to the streamflow decline has increased significantly compared to the 1980 s.Large-scale afforestation and water withdrawal,reservoir storage are the main ways that humans affect regional streamflow.(2)With 2007-2008 as the warm-up period,2009-2012 as the calibration period,and 2013-2015 as the verification period,the SWAT model was used to simulate the streamflow process of six hydrological stations(Shixiali,Xiangshuibao,Tianzhen,Chaigoubao South,C haigoubao East,and Zhangjiakou Station)in the upper Yongding River basin.Among them,the simulation results of Shixiali Station(Calibration period R~2=0.77,ENS=0.57,Verification period R~2=0.79,ENS=0.66)and C haigoubao East Station(Calibration period R~2=0.79,ENS=0.61,Verification period R~2=0.86,ENS=0.79)are better,and the results of Tianzhen Station(Calibration period R~2=0.45,ENS=0.44,Verification period R~2=0.72,ENS=0.72)and C haigoubao South Station(Calibration period R~2=0.41,ENS=0.29,Verification period R~2=0.63,ENS=0.47)are average,but the results in Xiangshuibao(Calibration period R~2=0.12,ENS=-0.07,Verification period R~2=0.22,ENS=-0.16)Station and Zhangjiakou(Calibration period R~2=0.33,ENS=0.29,Verification period R~2=0.48,ENS=0.22)is so bad.In general,the simulation effect in the flood season is better than the dry season,the simulation effect in the upper reaches of the Yang River is better than the lower reaches,and the monthly scale simulation effect in the Sanggan River Basin is better than that in the Yang River Basin but the annual scale simulation effect is opposite.The main reasons for the poor simulation results of some stations and periods include the model's inadequate consideration of the natural-social dual water cycle process,the model's inability to characterize the spring river thaw process,and its poor ability to characterize soil water and groundwater.(3)Compared with the historical period(1956-2003),the current situation(2009-2015)of surface water resources distribution in Zhangjiakou City has not changed.The amount of surface water resources in the inland river basin and Luan river basin is relatively small.The surface water resources in the Yongding river basin,Chaobai river basin and Daqing river basin are relatively abundant,but the total volume has been greatly reduced.The deterioration of suface water resources is most obvious in the urban area of Zhangjiakou C ity,Yuxian-Yangyuan Basin,and Zhuolu-Huailai Basin where has a relatively high degree of population concentration and relatively developed industries.Under the RCP4.5 and RCP8.5 scenarios,with the increase of future precipitation and frequent occurrence of extreme hydrological events(2026-2100),the streamflow during the flood season will increase in Upper Yongding River Basin.Compared with the surface water resources in 2009-2015,except for 2076-2100 under the RCP4.5 scenario,the surface water resources in Zhangjiakou will be significantly improved,and the amount of surface water resources in some periods will be close to 1956-2003.