Evaluation And Optimization Of Water Resources Carrying Capacity In Liuyang City Based On HWA Framework

More research has revealed that central China is one of the most vulnerable areas to a water crisis because of limited and unequally distributed water resources as well as rising water demands.Also,climate change is expected to reduce water resources dramatically,resulting in increased competition among users and severe water shortages for irrigated agriculture.What’s more,agricultural water use is also an indispensable water use unit in county(county-level city)region,which is urgent to optimize the allocation of water resources.Liuyang City was chosen as a typical study area.Firstly,the water supply and consumption structure were analyzed,and water resources carrying capacity(WRCC)was evaluated in historical periods 2015～2021.The“Human-Water-Agriculture”framework was proposed to evaluate the WRCC,which included carrier body(water resources system)and bearing objects(human system and agricultural system).Additionally,the quota analysis method was used to calculate the water demands in planning year based on the water consumption structure in historical periods,and then the WRCC was evaluated.The results showed that the water resources would be seriously overloaded and be in a non-high bearing state.Finally,Genetic Algorithm(GA)was used to optimize the allocation of water consumption of the planning year under the premise of the constraints such as the red line of cultivated land,food security and water supply,so as to achieve the maximization of water supply and consumption security of the human and agricultural system and economic benefits.The results are as follows:(1)Water supply for water conservancy projects was the main water supply mode,accounting for about 87.4%of the total water supply,followed by about 7.2%for municipal projects,2.8%for self-provided water supply,and 2.6%for non-water conservancy projects in historical periods.In terms of water consumption structure,the water consumption of human system(composed of domestic,industrial and ecological water consumption)accounted for about 35.7%of the total water consumption,and the water consumption of agricultural system accounted for about 64.3%,indicating that the water demand for agricultural development was large.In terms of WRCC,the WRCC of the human system in 2018 and 2019 was in a moderate state,while was high or very high in other years.And the WRCC of agricultural system was very high,which was in a harmonious state between agriculture and water resources system.(2)The water supply was 9.65×10~8 m~3 and 13.21×10~8 m~3 at 90%and 75%guarantee rate in the planning year,while the water demand was 17.72×10~8 m~3and 15.06×10~8 m~3 respectively according to the water consumption model in historical periods,which was far more than the water supply.In terms of water use structure,the ecological water consumption was only 2.5%and 2.9%of the total water consumption at 90%and 75%guarantee rate,indicating that there was a phenomenon that other water consumption squeezed the ecological water.In terms of agricultural planting structure,planting area of rice accounted for about 50%of the total crop planting area at most;while the proportion of economic crops with high economic benefits such as fruits,flowers and flue-cured tobacco were less than 7%.Therefore,this planting structure should be optimized.As respect to WRCC,the WRCC of human system and agricultural system were in a low and moderate carrying state respectively at 90%and 75%guarantee rate;and there was an inharmonious phenomenon among human system,agricultural system and water resources system.The WRCC should to be optimized and improved.(3)GA was used to optimize the allocation of water consumption of each water consumption unit in the planning year,so as to achieve the comprehensive objectives of water supply and consumption security of human system and agricultural system,and economic benefits maximization under the premise of the constraints of farmland red line,food security and water use.The results showed that:the water consumption was 9.64×10~8 m~3 and 10.63×10~8m~3 at 90%and 75%guarantee rate,which was less than water supply and significantly better than the carrying capacity without optimization.The proportion of ecological water consumption increased to 6.1%and 8.4%,indicating that the importance of ecological water use was not neglected.As respect to planting structure,the planting structure not only maintained a high planting proportion of water-saving crops,but also increased the planting proportion of cash crops on the basis of achieving food security.In terms of WRCC,the WRCC of both the human system and agricultural system were in a very high carrying state at 90%and75%guarantee rate.The study has far-reaching significance for achieving sustainable development of water resources.In addition,it could provide a reference for the evaluation and optimal allocation of WRCC in other regions.