Study On The Contribution Of Water Conservation Function To River Runoff In The Hanjiang River Basi

With the impact of global climate change and human activities,terrestrial ecosystems are being damaged to varying degrees,resulting in a more prominent contradiction between water supply and demand,especially in drought-prone and flood-prone areas.Therefore,regional ecological protection and restoration are crucial for enhancing the water conservation function of ecosystems and alleviating the contradiction between water supply and demand.The water conservation function is an important component of the hydrological cycle within a watershed and plays a vital role in maintaining the dynamic balance of water volume,protecting water environment,reducing flood peaks,and improving ecology.The contribution of the water conservation function to river runoff can reveal its regulation and storage capacity and evaluate its impact on basin runoff.This provides a scientific basis for water resource utilization,water environment protection,and ecological restoration in the Han River basin.Using the In VEST model,the water yield of the basin was calculated,and the water conservation function was assessed based on factors such as flow velocity coefficient,soil saturation hydraulic conductivity,and topographic index.Basic data such as digital elevation,meteorology,land use,soil,and hydrology were collected,and a distributed hydrological model,SWAT,was used to simulate the river runoff in the Han River basin.Finally,the contribution of the water conservation function of different scales of sub-basins to river runoff was calculated to provide a basis for watershed management,ecological protection and restoration,and water resources security management.The main research conclusions are as follows:(1)The total water conservation capacity of the Han River basin is 10.11×l0~9m~3,and the average water conservation function is 54.30 mm.The spatial pattern of the water conservation function decreases from east to the central part and increases near the western part.The water conservation function varies significantly with different vegetation types,with forest having the strongest function,followed by shrubland,grassland,cultivated land,and urban land.(2)The SWAT model is used to simulate the water volume of the Han River Basin,and the characteristics of runoff and water volume changes in the basin are obtained.According to the SWAT-CUP tool,the parameter sensitivity analysis is carried out and the highly sensitive parameters are calibrated.The calibration results show that:the regular R2,NSE and PBIAS of the Hanzhong station rate are 0.66,0.62 and 4.8%,and the verification periods are 0.63,0.60 and 5.2%respectively;the regular R~2,NSE and PBIAS of the Ankang station rate are 0.69 and 0.65respectively and 4.4%,the verification period was 0.67,0.62 and 4.9%respectively;the R~2 and NSE of the Danjiangkou Reservoir Hydrological Station during the simulation period were 0.72and 0.65,and the PBIAS was 5.7%,indicating that the overall simulation effect of the model is good,and the simulation results meet the requirements.Basically,it can reflect the runoff characteristics of the Han River Basin.(3)Based on the SWAT model,the water conservation and runoff of three typical land use types,including forest,grassland,and unused land,were calculated at different temporal scales,and correlation analysis was performed,showing a negative correlation between the water conservation function and runoff with correlation coefficients of-0.84,-0.80,and-0.68,respectively.(4)Combining the results of the SWAT model with hydrological and rainfall data,the contribution of the water conservation function to river runoff was calculated,with the contribution rate ranging from 1%to 60%,and the majority of the contribution rate falling between 30%and40%,representing the overall ecological features of the watershed with good hydrological processes and ecological functions.Areas with a contribution rate below 10%may be prone to flood disasters.(5)The graded results of the contribution rates of sub-basins at different scales and the graded results of the strengths of water conservation functions were superimposed for analysis.The conclusions are as follows:1)Regions with relatively high contribution rates(moderate-high and high contribution rates)are mainly distributed in the western and central parts of the basin,while regions with relatively low contribution rates(low and moderate-low contribution rates)are mainly distributed in the northeast and some parts of the central and western regions of the basin.2)The contribution rates of small and medium-sized sub-basins can better demonstrate the relationship between water conservation function and runoff than those of large-scale sub-basins.3)Sub-basins with weak water conservation functions have generally lower contribution rates,while sub-basins within high-grade water conservation areas have higher contribution rates.4)Small-scale sub-basins can better reflect the corresponding relationship between water conservation function and contribution rate in spatial distribution.