Optimal Allocation Of Water Resources In Shule River Basin Based On Adjustment Of Planting Structure Under Climate Change

Shule River Basin is a typical inland river basin in arid area of Northwestern China.Water resources are an important factor restricting the sustainable development of local social economy.In recent years,the dual driving forces of climate change and human activities,as well as perennial excessive water use,have led to a series of environmental problems in the basin,such as water shortage,groundwater level decline,vegetation degradation,land desertification and so on.In the Shule River Basin,agricultural irrigation water accounts for more than 80%of all types of water consumption.Therefore,under the premise of ensuring the continuous improvement of social and economic level and ecological environment in the future,the optimal allocation of water resources,especially the optimization of agricultural water use and planting structure,is very important for the sustainable development of the basin.Using SWAT model,this paper chooses three future climate change scenarios of RCP 2.6,RCP 4.5 and RCP 8.5 proposed by IPCC to carry out the simulation study of water resources in Shule River Basin from 2020 to 2050,and uses grey model to predict future water use of industrial,residents,urban public utilities,forestry,animal husbandry and fishery.By introducing the index of utilization rate of water resources,the proportion of ecological water consumption in the basin was increased,and the available water for future agricultural irrigation is ultimately obtained.Meanwhile,through data collection and questionnaire survey,the basic data of cost,income,yield and irrigation water consumption of the main crop types in Shule River Basin were obtained,and the multi-objective optimization model of agriculture in Shule River Basin was constructed.Agricultural planting structure and corresponding water resources optimization under three future climate change scenarios in the Shule River Basin were carried out by using multi-objective genetic algorithm.,At the same time,the evaluation of effect of water-saving technology on agricultural development in Shule River Basin was made,and the optimal allocation of water resources in the future was realized.The main conclusions are as follows:(1)Water consumption in Shule River Basin increased from 2005 to 2010 and decreased from 2011 to 2017 gradually,of which more than 80%of the total water consumption for agricultural irrigation is occupied throughout the years.From 2011 to2017,with the decrease of irrigation water consumption,the planting area of cotton,wheat decreased,while the planting area of corn,vegetables,medicinal materials increased year by year.(2)A satisfactory simulation effect by SWAT models to the hydrological status of Shule River Basin was get.The simulation results of monthly scale data showed that the efficiency coefficients of each hydrological station are above 0.55.The water resources under three climate change scenarios during 2020-2050 are simulated.The results showed that with the increase of greenhouse gas concentration in RCP scenarios,the total water resources showed an increasing trend.The average annual water resources of RCP 8.5 are 2.92 billion m~3,RCP 4.5 is 2.83 billion m~3 and RCP 2.6 is2.75 billion m~3,which are higher than the average annual water resources of 2005-2017.(3)The grey model is used to predict the water use of industrial,residents,urban public utilities,forestry,animal husbandry and fishery in the period of 2020-2050.The results showed that industrial water and water for forestry,animal husbandry and fishery decreased year by year,while urban public and residential water consumption increased year by year.(4)In order to ensure the ecological water consumption in the basin,the utilization rate of water resources in the basin has been reduced year by year from 2020 to 2050,and the water resources utilization will finally get to the planning target of 24%by 2050.The ecological water consumption in 2020 to 2050 has been predicted,and then the available water for agricultural irrigation has been obtained.The results showed that with the decrease of water resources utilization rate year by year,the available water for agricultural irrigation decreased separately from 872 million m~3(RCP 2.6),913million m~3(RCP 4.5)and 954 million m~3(RCP 8.5)in 2020 to 560 million m~3(RCP2.6),464 million m~3(RCP 4.5)and 418 million m~3(RCP 8.5)in 2050.(5)Aiming at maximizing agricultural profit,agricultural output value and irrigation water use benefit in Shule River Basin,a multi-objective optimization model of agriculture was established to optimize agricultural planting structure and irrigation water consumption.The results showed that the crop planting structure in Shule River Basin should be adjusted to be dominated by seed productions,spice crops,wheat and corn.With the increase of greenhouse gas concentration set in RCP scenarios,the area of spices and seed productions showed an increasing trend.Corresponding to the adjustment of crop planting structure,the water consumption of wheat,corn,seed productions and spices accounted for a larger proportion of the total water consumption of agricultural irrigation in the three scenarios.According to the optimized agricultural profit,agricultural production value and water use benefit,the agricultural profit under RCP 8.5 scenario is the highest,followed by RCP 4.5,and which under RCP 2.6scenario is lowest.It shows that climate warming may be beneficial to water resources supply and agricultural comprehensive benefits in the basin without considering other negative impacts of climate warming on society,economy and environment.(6)Setting up scenarios of different water saving rate,optimization and analysis of the agricultural profit,agricultural production value and water use benefit under the application of water saving technology was achieved.The results showed that the higher the water saving rate is,the higher the total agricultural income,total agricultural output value and water use benefit are.From the above,this study obtained the change of water resources in Shule River Basin under the background of future climate change by hydrological model simulation method;predicted available water for agricultural irrigation in the future on the premise of ensuring ecological water security;on this basis,the future agricultural planting structure and water allocation were optimized by building a multi-objective optimization model for agriculture.The results showed that in the context of future climate change,in order to protect the ecological environment,the win-win development goal of reducing agricultural water resources and improving agricultural benefits can be achieved through optimization adjustment.The results will provide scientific reference for agricultural development,ecological environment protection and water resources development and utilization in arid areas.