Water-Food-Energy Nexus Analysis In Canal And Well Combined Irrigated Area Based On Coupled Model

Water,food,and energy are vital resources to maintain human survival and sustainable social development.The increase of global population,the acceleration of urbanization and the rapid development of economy have promoted the demand for water,food and energy.About 70%of the global groundwater is used for agricultural production.The pursuit of food production by human beings makes agriculture’s dependence on groundwater continuously increase,which will directly lead to the increasing demand for energy in food production and its supply chain.Taking the water-food-energy(WFE)nexus as the research object of multi-objective optimization problem,it is of great significance to scientifically allocate limited water resources and energy to meet the food demand of the agricultural sector,and to promote the coordinated and high-quality development of regional resources.China is a great agricultural country.Jinghuiqu irrigation area is an important foundation of agricultural development in Guanzhong plain and undertakes the important task of grain production in Shaanxi Province.The canal and well combined irrigation method can make groundwater as an important supplement when the surface water needed for irrigation is insufficient.Irrigation and crop yield and energy consumption have inseparable connection.Optimizing the WFE nexus in irrigation area can effectively alleviate the current situation of resource contradiction in irrigation area.Therefore,this study takes Jinghuiqu irrigation area as the research area,and constructed crop model Aqua Crop,groundwater numerical simulation model MODFLOW and energy model DEG＿GI for the irrigation area.They are closely coupled based on Python language to generalize the WFE nexus in the irrigation area,and then it is optimized by NSGA-Ⅲalgorithm in the multi-objective optimization framework Pymoo.Finally,the entropy weight method and TOPSIS were used to make decisions on the Pareto frontier after optimization.The comprehensive management of food,water resources and energy sectors has been realized.The sustainable and high-quality development of the three sectors has been promoted.The conclusions are as follows:(1)According to the field data,the Aqua Crop of winter wheat in Guanzhong plain was constructed.After adjusting parameters such as CCx,CDC and CGC,the performance of the model was evaluated according to simulated data and measured data.The NRMSE,R~2 and NSE values of CC were 10.27%,0.82 and 0.90 respectively,while those of B were 26.70%,0.80 and 0.85 respectively.Six multi-objective optimization scenarios are constructed for three typical hydrological years.NSGA-III algorithm,the entropy weight method and TOPSIS are used to solve and decisions making on multi-objective optimization problems.The results show that the Pareto frontier after optimization in dry years has the greatest difference and the most obvious optimization effect.(2)According to the hydrogeological situation and aquifer structure of Jinghuiqu irrigation area,the irrigation area was divided into different hydrogeological areas.Different permeability coefficient and specific yield are input for each area.The above hydrogeological parameters and source and sink terms are input into GMS to form the MODFLOW model of irrigation area.The PEST in GMS is used to automatically adjust the permeability coefficient and specific yield in the model,so that the error between the simulated value and the measured value of groundwater level is minimized.The period from January 2007 to December 2008 is taken as the calibration period of the model,and January to December 2009 is taken as the validation period of the model.The results show that the MODFLOW model constructed in this paper can accurately simulate the dynamic changes of groundwater in irrigation areas and has high reliability.Finally,an ideal example was built in Flo Py,which lays a foundation for building MODFLOW in Python platform.(3)Based on Python platform,the crop model ACOSP,groundwater numerical simulation model Flo Py and energy model DEG＿GI were closely coupled,and the WFE nexus in irrigation area is generalized,and then the WFE nexus is optimized by NSGA-III algorithm in the multi-objective optimization framework Pymoo.The objectives of these multi-objective optimization problem are:the minimum average drawdown of groundwater grid caused by irrigation(W),the maximum sum of crop yield per mu(F),and the minimum irrigation energy consumption per hectare(E).Finally,the entropy weight method was used to calculate the weights of the three optimization objectives,and the weights were brought into TOPSIS to sort the optimized solution sets.(4)In the sorted solution set,the solutions ranked first,50%and last are selected as three optimization scenarios in three typical hydrological years.The three optimized objectives values of Scenario 1 in the drought year are 3468.98 kg/mu,0.87m and 736.71KWh/ha;Scenario 2:3498.50kg/mu,0.99m,780.82KWh/ha;Scenario three is 3509.20kg/mu,1.28m and 905.19KWh/ha.The three optimized objectives values of Scenario 1 in the normal year are 3554.83kg/mu,0.49m,598.65KWh/ha;Scenario 2:3562.13kg/mu,0.57m,618.54KWh/ha;Scenario 3:3575.48kg/mu,0.76m,689.60KWh/ha.The three optimized objectives values of Scenario 1 in the wet year are 3645.12kg/mu,0.38m,509.49KWh/ha;Scenario 2:3646.25kg/mu,0.40m,511.90KWh/ha;Scenario 3:3648.62kg/mu,0.52m,525.19KWh/ha.