Optimal Allocation Of Agricultural Water Resources Based On Water-Carbon Footprint

Water scarcity and carbon disasters are fundamental challenges to China’s sustainable development.Water consumption in agriculture is a significant contributor to water scarcity,consuming more than 60%of the country’s total water use.Meanwhile,agricultural production causes a large amount of carbon emissions,accounting for 24%of total carbon emissions from human activities.Therefore,the rational allocation of water resources and the reduction of carbon emissions in agricultural production are vital measures to alleviate China’s water shortage and to achieve China’s "double carbon" strategic goal.In this study,the water and carbon footprints of crop production in Jiangsu Province were calculated by the "bottom-up" and "life cycle analysis" methods.Under the perspective of water-carbon footprint,the multi-objective optimization models of "economy-water resources" and"economy-water resources-carbon emissions" were constructed,respectively.The decomposed simplex aggregation algorithm(DSMA)and decomposed simplex aggregation backtracking algorithm(DSMAB)were proposed.The optimal water allocation scheme and water-carbon trading flow in Jiangsu province were obtained.The results of this study can provide a theoretical basis and countermeasures for water allocation and management,agricultural cultivation structure optimization,and carbon reduction and sequestration technology.Firstly,the green water footprint(GWF)and blue water footprint(BWF)of six crops in 21 water resource zones of Jiangsu Province were calculated.The results are as follows.The average GWF of six significant crops in Jiangsu province were,cotton(2307 m3/t)>peanut(598 m3/t)>rape(546 m3/t)>wheat(354 m3/t)>maize(336 m3/t)>rice(327 m3/t).Their spatial fluctuations were around 12.9%.The overall spatial distribution of GWF for dry season crops(wheat and rape)increased from north to south.The average BWF for the six major crops in Jiangsu Province were,cotton(1005 m3/t)>rape(865 m3/t)>wheat(495 m3/t)>rice(287 m3/t)>peanut(235 m3/t)>maize(101 m3/t).Their spatial fluctuations were around 24.1%.The rainy season crops(rice,maize,peanut and cotton)show an increasing trend from north to south,while the dry season crops show the opposite characteristics.Based on the distribution characteristics of the water footprint in Jiangsu Province,an"economic-water resources" multi-objective optimization model was constructed under the perspective of virtual water trade.The model takes the acreage of crops in each water resource zone as the decision variable and the economic trade and water saving as the objective function,considering the land,water,and area constraints.The DSMA algorithm was proposed to obtain the global optimal solution for the "economic-water resources" in Jiangsu Province,considering the model’s non-linear,strong constraint and high-dimensional characteristics.The results are as follows.Compared to the actual planting scheme,the water optimization scheme reduces the area planted with cotton by 65%,rape by 30%and peanuts by 7%while increasing the area planted with rice,maize and wheat by about 11%.The agricultural yield of the scheme was increased by 8%,with an economic trade yield of 765×108 RMB.The blue water footprint of agricultural production was reduced by 2%,with a total blue water footprint of 101×108 m3.The virtual blue water trade increased by 118.1%.In this study,the carbon footprint per unit area(CFA)and carbon footprint per unit yield(CFY)of six major crops in Jiangsu Province were estimated,and their carbon footprint composition and parameter sensitivity were analyzed.The results are as follows.The CFA of six crops in Jiangsu province are,rice(5790.65 kg/ha)>maize(4993.87 kg/ha)>wheat(4268.49 kg/ha)>peanut(3841.29 kg/ha)>oilseed rape(3601.30 kg/ha)>cotton(3433.21 kg/ha).The CFY of six crops are in the opposite order of The CFY,cotton(2.70 kg/kg)>rape(1.22 kg/kg)>peanut(0.94 kg/kg)>maize(0.83 kg/kg)>wheat(0.75 kg/kg)>rice(0.65 kg/kg).The carbon source of the carbon footprint of agricultural production in Jiangsu province mainly consists of fertilizer application(32.5%of the total carbon source),soil emissions(29.2%)and electricity used for agricultural processing(19.3%).The carbon sink mainly consists of carbon sequestered by straw returning to the fields(31.2%of the total carbon sink)and carbon sequestered by crop roots(68.8%).According to the parameter sensitivity analysis,the three parameters that have a large impact on the carbon footprint of six crops production in Jiangsu province are the carbon emission coefficient of electricity(μelec),electricity used for agricultural processing(delec-fp),and fertilizer use(dfer).Based on the distribution characteristics of the water-carbon footprint of each crop in Jiangsu Province,The multi-objective optimization model of "economy-water resources-carbon emissions" was constructed.The model uses economic trade,water saving,carbon emission and low carbon agricultural competitiveness as four objective functions,land resource,water resource and area as the constraints,and the crop planting area of each water resource zone as the decision variables.The DSMAB algorithm was proposed for the model.The "economy-water resource-carbon emission" optimization scheme was obtained for Jiangsu Province.The results are as follows.The optimized scenario increases the area planted with cotton by 156%,rice by 11%and wheat by 11%,reduces the area planted with maize by 100%,peanuts by 42%and rape by 30%.Compared to the actual planting scenario,the optimized scenario increases the economic trade return of agriculture by 10%reaching 781×108 RMB,reduces the carbon footprint of agricultural production by 1%,with a production carbon footprint of 201×108 kg,and increases the low carbon competitiveness of agriculture by 4%reaching 0.059.virtual blue water trade was 7.42×108 m3,with an increase of 235.7%.