Optimal Allocation Of Soil And Water Resources And Spatial Pattern Optimization Of Planting Structure In Aksu River Basin

ater and soil resources are the basic resources for human survival and development,Which are located in typical arid oasis areas such as the Aksu River Basin.Aksu River Basin is a typical inland oasis area in Northwest China.In recent years,with the impact of climate change and human activities,there are a series of problems in the Aksu River Basin,such as the shortage of water resources,the decline of underground water level and the destruction of ecological environment.Therefore,under the background of climate change,how to realize the rational distribution of water and soil resources in the watershed on the premise of ecological protection is an urgent problem to be solved.At the same time,Aksu River Basin,as a typical oasis agricultural area,agricultural water consumption accounts for more than 80%.Accurate acquisition of crop planting structure in the basin and optimization of spatial pattern of agricultural water consumption and planting structure are the key issues in the allocation of water and soil resources in the basin.On the basis of summarizing and analyzing the research progress at home and abroad,this paper first uses the SDSM method to downscaling based on the Can ESM2 model,predicts the temporal and spatial changes of the main meteorological factors in the watershed in the future,and then uses the crop coefficient method and the neural network model to predict and calculate the watershed future.Water demand and water supply.After that,a multi-objective optimization model that simultaneously considers economy,society and ecology under different scenarios was constructed to realize the optimal allocation of water and land resources in the basin under climate change.At the same time,based on domestic GF-1 data,a multi-temporal NDVI change curve for different crops was constructed,combined with field survey data,and supervised classification methods were used to obtain the current planting structure in the oasis area of the watershed.Based on this,the current oasis area was analyzed.Spatial distribution of agricultural water demand.A multi-objective crop planting structure spatial pattern optimization model was constructed,and the double optimization of the number and spatial layout of crop planting structures in the Aksu River Basin was realized.The main conclusions of this article are as follows:(1)Based on climate change simulation,the changes in water demand and water supply under different climate scenarios in the Aksu River Basin are analyzed.In the future climate scenarios of the Aksu River Basin,climate changes are mainly manifested as increased temperature and decreased rainfall.The range of changes in meteorological factors under the RCP8.5 scenario is greater than that under the RCP4.5scenario.In the future climate scenario,ET₀ in the Aksu River Basin will increase at a rate of10.02 mm/10a and 16.65 mm/10a under the two scenarios of RCP4.5 and RCP8.5.The increase in ET₀ will lead to an increase in water demand for vegetation in the watershed.With the advancement of water-saving irrigation technology,the growth rate of water demand per unit area of different land types in the watershed will slow down.At the same time,the temperature rise has accelerated the melting rate of glaciers in the northern mountainous areas of the basin,and the surface runoff under the two climate scenarios before 2050 is on the rise.On the basis of reducing the amount of groundwater extraction,the amount of water resources available in the basin will still increase slightly before 2050,and the increase under the RCP8.5scenario is greater than that of RCP4.5.(2)Based on the multi-objective optimization model of water and soil resources,the optimal allocation of water and soil resources in different scenarios under the ecological background of the Aksu River Basin has been realized.At present,under the premise of meeting ecological water consumption,the water shortage in the basin is 7.61×10⁸ m³.In order to meet the water supply and demand balance of the basin under the current situation,the basin should reduce the area of arable land to reduce the corresponding agricultural water use.Through multi-objective model solution and solution set optimization,the arable land should be reduced by 950.7 km² under the current configuration,mainly in Awati County and Aksu City.Areas with high water demand per unit area of cultivated land,such as the city of Alar,account for about 17%of the total cultivated land.Taking into account the ecological protection of the river basin,the forest land and water area of the river basin continued to increase in the medium-term planning year and the long-term planning year.At the same time,with the advancement of water-saving technology,by2050,the Aksu River can provide more ecological restoration water for the downstream Tarim River under the premise that the cultivated area is not less than 4500 km².(3)Based on multi-temporal GF-1,meteorological and irrigation data,the spatial distribution of crop planting structure and water demand in the oasis area of the Aksu River Basin is analyzed.Under the multi-temporal NDVI sequence,the maximum likelihood method classification result is the best in the supervised classification,with an overall accuracy of 93.08%and a Kappa coefficient of 0.913.The supervision classification results show that grain crops(rice,corn,wheat)are mainly distributed in Wushi County and Wensu County in the upper reaches of the basin;cash crop cotton is mainly distributed in Aksu City,Alar City and some farms of Nongyi Division;fruit trees are mainly distributed In Aksu City and Awati County.Due to the influence of climate and crop planting structure,there are large differences in the spatial and temporal distribution of crop water demand and irrigation water in the basin.In terms of time,the water demand in spring and summer accounts for about 70%of the annual water demand;spatially,the water demand and irrigation in the watershed near Wensu County The amount is significantly higher than other regions.In addition,the water demand of the same crop varies in different regions.For example,the annual water demand of cotton is between 509.5 and553.3 mm,and the difference in water demand in different regions is 43.8 mm.(4)Based on the spatial optimization model of multi-objective crop planting structure,a method for optimizing the spatial pattern of watershed planting structure is proposed.The multi-objective spatial pattern optimization model with the goal of planting benefits,the sum of monthly average NDVI of the river basin,and the conversion cost of planting structure can realize the spatial pattern optimization of planting structure in the Aksu River Basin under the premise of"killing wells and reducing fields and returning farmland to forests".Comparing the solution results of different algorithms for the spatial multi-objective model,the MOPSO algorithm performs best.Through optimization,the area of arable land has been reduced by about 18%,which is similar to the results of optimization of water and soil resources in the previous chapter.The reduction of arable land was mainly in the 1st Regiment and 2nd Regiment of Nongyi Division and the western area of Aksu City.In conclusion,the future climate change of the basin is mainly manifested by temperature rise and rainfall decrease,and climate change will change the supply and demand of water resources.The multi-objective soil and water resource optimization model under different scenarios can achieve the economic-society-ecological optimization under the premise of ecological protection.High-resolution satellite data can be used to extract complex planting structures in the watershed.Based on this,the spatial pattern optimization model of multi-objective planting structures can achieve dual optimization of crop planting quantity and spatial layout on the premise of ensuring grain self-sufficiency.