Hydrological Simulation And Water Resources Management Strategy Of Danjiang River Basin Based On VIC Model

The Danjiang River Basin is one of the important water conservation areas in the "Qinling Mountains",the boundary between the north and south of China in terms of climate and natural geography.It is also an important water source area for the Middle Route of the South-to-North Water Diversion Project.In recent years,with the increasing impact of climate change and land use changes on the water cycle of the basin,as well as changes in industrial and agricultural production and even regional economic development,the water resources in the Danjiang basin have also undergone corresponding changes.Therefore,it is of practical significance to the management of water resources in the Danjiang River basin to make researches into the runoff and hydrological changes in the basin via hydrological modeling.This paper took the Danjiang River Basin in Shaanxi Province as the study area,and built the VIC hydrological model to conduct hydrological simulations to analyze the characteristics and causes of runoff changes in the basin.At the same time,it also predicted the future change of runoff in the river basin,and finally put forward the water resources management countermeasures of the Danjiang river basin.This paper first used the monthly runoff observation data of Danfeng Hydrological Station in the Danjiang River Basin of Qinling Mountains to calibrate the model to localize the parameters,and then established the VIC hydrological model.Then the model is verified with the data of the runoff of the river basin's outlets collected by the Zijingguan Hydrometric Station,the Zhulinguan Hydrometric Station and the Wuguan Hydrometric Station in their actual measurement.Thus the VIC hydrological model is established of the Danjiang River basin within Shaanxi province.Verification is made of the applicability of the model in the Danjiang River basin,and an analysis is made of the inter-regional differences of the VIC hydrological model's runoff modeling within the river basin so as to simulate the hydrological processes in the past and predict the runoff changes in the river basin in the future.By analyzing the driving factors of runoff changes in the basin,the runoff changes was studied under the trend of land use changes and climate change,and a comprehensive analysis framework for runoff changes was constructed to evaluate the ecological flow and ecological water demand of the basin.Finally,the Danjiang River Basin water resources management countermeasures were proposed,which provide a useful reference for the research on the hydrological response of the river basin under the changing environment and the utilization and management of the Danjiang River water resources.The major work and conclusions are as follows.(1)Through the processing of DEM,vegetation,soil,and meteorological driving data,the model parameters of the basin were prepared,and the VIC hydrological model was constructed.The model was applied to the Danjiang River Basin in the Qinling Mountains after adjustments of the parameters were made according to the data of the monthly runoff measured by the Danfeng Hydrometric Station,the data of the runoff observed in Shaanxi Province's Hydrometry Monitoring of the Danjiang River Basin,and the data of the daily and monthly runoffs measured by the Zijingguan Hydrometric Station.At the same time,the application of the VIC hydrological model in the Danjiang River Basin was detected using the data from the Wuguan Hydrological Station and Zhulinguan Hydrological Station,and the temporal and spatial distribution of water resources in the basin was analyzed.The results show that the Nash efficiency coefficient in calibration period and verification period were 0.82 and 0.81 respectively when used the data measured by Danfeng Station for verification,and the VIC Land Surface Hydrological Model could reflect well the daily and monthly runoff processes in the Danjiang River basin in Shaanxi province.In addition,the relative errors of the calibration period and the verification period were 4.51% and 2.13%,respectively,which could well simulate the water balance of the basin.By means of parameter transplantation,the VIC hydrological model established at Danfeng Station was used for calibration and verification in the Danjiang River Basin of Shaanxi Province,and the applicability of the model was verified by the runoff data of the provincial exit section.This fully shows that the VIC hydrological model has a certain applicability in the Danjiang watershed of the Qinling Mountains at the small and medium watershed scale.(2)Combined theoretical analysis and model simulation,on the basis of runoff laws,the driving factors of runoff changes in the basin were analyzed from the climate change that affects the meteorological driving conditions of the upper boundary of the model and the land use change that affects the vegetation change of the underlying surface of the lower boundary of the model.Based on the method of climate elasticity coefficient in Budyko's hypothesis and the VIC hydrological modeling,the attribution analysis of runoff changes within the Danjiang River Basin was carried out..The results show that the contribution of climate change and human activities to the runoff changes in the Danjiang River Basin has significant spatial differences in some sections of the basin.Specifically,Compared with the Wuguan River Basin,Yinhua River Basin,and the downstream areas located in the middle and lower reaches,the impact of changes in underlying surface conditions is more significant for Shangzhou District and Danfeng County which located in the upper reaches of the regional basins and the centers of regional population,industrial and agricultural production,social and economic development,and human activities.Viewed from the response relation between land use/land coverage changes and the runoff,certain correlation is worked out between changes in land use and changes in the runoff in the Danjiang River basin.When grassland and cultivated land decrease,forest land increases,and this trend is in agreement with the trend that the decrease in grassland and the returning of farmland to forests can result in increased evapotranspiration and river shutoff and thus decreased runoff.(3)As to runoff changes and the changes in hydrological conditions in the Danjiang River Basin in the past 50 years,the established distributive VIC hydrological model of the Danjiang River Basin was used to simulate the long-term daily runoff processes in the river from 1961 to 2019.On this basis,combined with the ecological flow(ecological surplus and ecological insufficiency)and IHA indicators,the changes in the hydrological situation of the Danjiang River Basin were analyzed,and the ecological water demand evaluation method of the Danjiang River Basin was constructed to evaluate the water demand status of the ecological environment of the basin.The result shows that in the past 50 years,the runoff in the Danjiang River Basin of Qinling Mountains has shown a decreasing trend,which is consistent with the decreasing thrend of precipitation in the basin.Since the 1990 s,human activities have further intensified the reduction of runoff,and the ecological flow has been generally in ecological insufficiency.The ecological environment water demand,especially for the downstream area,is obviously insufficient.(4)The down-scale data processing of the BNU-ESM,CC-CSM1.1(m),IPSL-CM5A-MR,CSIRO-MK3.6.0 and Can ESM2 modes of the new generation climate change situations CMIP5 of RCP2.6,RCP4.5 and RCP8.5 are used to drive the VIC hydrological model of the Danjiang River basin in agreement with the response of the runoff to temperatures and precipitation in simulated climate change,thus making predictions of the trends of runoff changes in the Danjiang River basin in the Qinling Mountains in future climate situations.The results show that the temperature in the Danjiang River Basin under future climate scenarios will continue to rise,and rainfall in most areas will show a decreasing trend.Due to the comprehensive influence of temperature and rainfall,the average runoff of the Danjiang River Basin will decrease in the future for many years.There will be different degrees of reduction in each month of the year.The decrease of the runoff during the flood season will be smaller,while the decrease of the runoff during the dry season will be more.It is extremely prone to drought disasters during the dry season,and the future water resources management of the basin will face challenges.(5)Based on the evaluation and prediction results of the above VIC hydrological model simulation,this paper has carried out water resources zoning on the Danjiang River Basin in the water source area of the South-to-North Water Diversion.Specifically,it includes the upper reaches of Danjiang Shangzhou District,the middle reaches of Wuguan Danfeng District,Shanyang Yinhua District,and the lower reaches of Shangnan District.At the same time,based on the specific water resources zoning status of the basin,combined the temporal and spatial distribution of water resources and the ecological water demand assessment simulated by the VIC hydrological model and the future water resources predicted by the VIC hydrological model coupling,the corresponding water resources management countermeasures was proposed.It can provide references for the division of river basin water resources,and theoretical support and countermeasures for local water resources management.The proposed management countermeasures mainly include water saving,high-efficiency water use,effective utilization and construction of water conservancy facilities,regional water and soil management,and regional protection of water resources.