Optimal Allocation Of Water Resources In Hongsibu District Of Ningxia Based On WEAP-MODFLOW Coupled Model

The Yellow River Basin,as the birthplace of Chinese civilization,has nurtured the splendid Chinese culture.In recent years,the water retention capacity of the upper and middle reaches of the Yellow River has significantly declined,leading to a continuous decrease in the river’s discharge.At the same time,the increasing agricultural irrigation area and rapid urban expansion within the basin have raised the rigid water demand,exacerbating the water supply-demand imbalance.Therefore,it is urgent to implement comprehensive measures for deep water conservation and control,optimize the water resources allocation pattern,and improve water resources utilization efficiency.Due to its arid climate,low rainfall,high evaporation,and poor natural water resources,the Hongsibu district in Ningxia has become one of the areas with prominent water resource issues in the Yellow River Basin.The region mainly relies on the transboundary water from the Yellow River to support its construction and development.However,due to constraints in initial water rights and industrial development water conditions,the region has low water resource utilization efficiency.To improve water resource utilization efficiency in the Hongsibu district and promote its sustainable and high-quality development,as well as provide a theoretical basis and technical support for ecological protection and high-quality development in other basins,this study selects the Hongsibu district in Ningxia as a typical research area.It constructs the WEAP and MODFLOW models separately and couples them using Link Kitchen software.Based on the coupled WEAP-MODFLOW model,optimization and allocation of surface water and groundwater resources are carried out,obtaining different water resource allocation scenarios for different planning years.Furthermore,the agricultural planting structure in the research area is further optimized based on the allocated water volume.The main results and conclusions are as follows:(1)By examining the runoff replenishment relationship between the supply and demand sides in the research area,the water cycle system in the study area is generalized using the WEAP model.Meanwhile,based on the hydrogeological characteristics and meteorological data of the research area,the MODFLOW module in the GMS software is used to construct a groundwater flow model.The accuracy of the model is validated using daily observed water level data,showing good precision in reflecting the changes in groundwater levels in the irrigation area.Finally,the Link Kitchen software is utilized to create a link file and couple the WEAP and MODFLOW models.The accuracy of the coupled model is evaluated using determination coefficient(R~2),Nash-Sutcliffe efficiency coefficient(NSE),and percent bias(PBIAS)based on the calibration of parameters using measured flow data from pumping stations.The results show that the calibrated coupled model has good accuracy,with R~2=0.98 and NSE=0.97 for the calibration period at monthly scale,and R~2=0.97 and NSE=0.97 for the validation period,indicating its ability to simulate the water resources situation in the research area.(2)Considering the current development status of the research area and the concepts of ecological protection and high-quality development in the Yellow River Basin,four key assumptions are set:reference scenarios,water-saving in urban and rural residents’daily lives,water-saving in agricultural irrigation,water-saving in industry,and population growth.By using a combination of these assumptions,16 research scenarios are established.The WEAP-MODFLOW coupled model is used to solve the water supply,water demand,and water deficit under each scenario.The results show that Scenario 7(S7)has the minimum available water supply and water demand,which are 167.8936×10~6 m~3 and 199.7388×10~6 m~3,respectively.In terms of water scarcity,Scenario 5(S5)has the smallest average water shortage index and average water deficit,which are 0.09229 and 17.6475×10~6 m~3,respectively.It can be observed that different combinations of single-factor key assumptions have a significant impact on the water supply-demand situation in the region.(3)Using economic and social benefits as the objective functions,the WEAP-MODFLOW model with the built-in MILP algorithm is employed to optimize the solutions.Through the analytic hierarchy process,the scenarios and corresponding water resource allocation plans that maximize the comprehensive benefits in the short-term planning year(2025)and long-term planning year(2030)are obtained.The scenario with the maximum comprehensive benefits in the short-term planning year is S14,with corresponding water allocation of 6.3571×10~6m~3 for domestic use,168.5026×10~6m~3 for agriculture,0.1626×10~6m~3 for industry,and 3.8751×10~6m~3 for livestock.In the long-term planning year,the scenario with the maximum comprehensive benefits is S5,with corresponding water allocation of 5.7753×10~6m~3 for domestic use,159.103×10~6m~3 for agriculture,0.1076×10~6m~3 for industry,and 4.0518×10~6m~3 for livestock.(4)The current planting structure in the research area was analyzed,and considering the characteristic economic industries in the area,with the objectives of maximizing total crop production,total crop value,and minimizing irrigation water consumption,and using the NSGA-II algorithm in the Pymoo multi-objective optimization framework,the agricultural planting structure in the research area was optimized.After optimization,for the near-term planning year,the optimized planting areas for corn,wheat,rapeseed,grapes,wolfberry,apples,daylily,and forage were 4513.68hm~2,441.04hm~2,6034.11hm~2,4926.75hm~2,3021.45hm~2,1813.77hm~2,778.93hm~2,and 1076.54hm~2,respectively.For the long-term planning year,the corresponding planting areas for the eight crops were 4613.91hm~2,721.4hm~2,5412.46hm~2,4760.96hm~2,2697.15hm~2,1892.55hm~2,1545.14hm~2,and 1227.95hm~2.Compared to the current baseline year,the total planting areas decreased by 1.37%and 0.21%for the near-term and long-term planning years,respectively.Specifically,for the near-term planning year,the planting areas of corn and wheat decreased by 52.9%and0.5%,while the planting areas of rapeseed,grapes,wolfberry,forage,apples,and daylily increased by18.4%,15.2%,8.9%,2.5%,6%,and 2.7%,respectively.For the long-term planning year,the planting areas of corn and wheat decreased by 52.7%and 0.7%,while the planting areas of rapeseed,grapes,wolfberry,forage,apples,and daylily increased by 15.4%,0.2%,16.3%,2.9%,9.8%,and 7.6%,respectively.The total crop value increased by 6.62×10~8 yuan and 6.47×10~8yuan for the near-term and long-term planning years,respectively,compared to the current baseline year.Meanwhile,the irrigation water consumption decreased by 5.90×10~8m~3and 9.45×10~8m~3for the near-term and long-term planning years,respectively.These results align with the strategic goal of promoting the development of animal husbandry and agriculture as advantageous industries in the hongsibu district,contributing to its high-quality development.