Hydrological Responses Of The Fuhe River Basin To Combined Effects Of Land Use And Climate Change

The hydrological cycle,also known as the water cycle,is an important link among multilayer surface processes that determines the spatiotemporal variability of water resources and the evolution of the surface environment under its auspices.Over the past century,the Earth’s climate system has undergone a significant warming trend,and global warming has been accompanied by increased human activity since the industrial revolution,leading to changes in water yield and routing mechanisms and,to varying degrees,in the characteristics of the regional hydrological cycle.Located in the middle and lower reaches of the Yangtze River and part of the Poyang Lake Basin,the Fuhe River Basin has a shallow average depth and is an area prone to seasonal heavy rainfall and flooding.Therefore,under the combined impact of climate change and anthropogenic land use/cover change,it is of great importance to make reasonable predictions of future regional hydrological response trends and water resource vulnerability to manage water resources in the Fuhe River basin.Moreover,awareness of possible future hydrological conditions allows proactive adjustment of adaptation strategies to make the future environment more habitable for human life.In this thesis,the SWAT and VIC models were first validated based on streamflow observations and then evaluated in terms of precision metrics and hydrological signatures.After the applicability and reliability of the two models were confirmed,the SWAT model was chosen to simulate the water cycle in future scenarios.The framework for future water resource assessment was then refined based on the outputs of the five CMIP6 GCMs under three SSP-RCPs.Future scenarios were constructed for three different time periods,namely,the 2030s(2025-2049),2060s(2050-2079)and 2090s(2080-2099).Based on this,the relative changes in water balance components and extreme flow frequencies in the Fuhe River Basin under these specific scenarios were predicted and analysed,and the spatiotemporal tendencies of future flow components and extreme hydrological events were obtained.The main results of this study are as follows:(1)The accuracy of SWAT(NSE=0.855,R2=0.856,PBIAS=2.3%,KGE=0.871,NRMSE=0.605)in the daily runoff simulations for the historical period 2010-2018 is comparable to that of VIC(NSE=0.875,R2=0.877,PBIAS=-6.5%,KGE=0.885.NRMSE=0.561),and the series consisting of 13 hydrological signatures are more strongly correlated with the measured series(Spearman correlation=0.98;Kendall correlation=0.93),which can well reproduce the hydrological processes in the basin,and the simulation is more efficient and applicable to the Fuhe River Basin.(2)Under future scenarios,the regional water cycle in the Fuhe River Basin will accelerate due to simultaneous changes in climate and land use,and the risk of extreme hydrological events will grow:flow is expected to increase by approximately 27.1%30.2%,24.7-39.0%and 35.5%-43.5%in the 2030s,2060s and 2090s,respectively.The increasing relationship between different scenarios is SSP1-2.6>SSP5-8.5>SSP3-7.0,whereby all SSP-RCP scenarios exhibit a greater change in runoff than in climate factors.Water availability increases significantly in February,August and October and decreases in November and December.The relative increase in surface runoff in densely populated downstream areas exceeds 100%,while groundwater decreases significantly over the same period,worsening the uneven distribution of water resources.(3)The range of uncertainty in predicting future extreme flows in the Fuhe River Basin increases with increasing return period,with future floods and droughts more likely to occur,more frequent and more severe in the SSP5-8.5 scenarios than in the SSP 1-2.6 and SSP3-7.0scenario.