| Agricultural water resources are the core strategic resources of agricultural production and food security.The supply and demand of water resources are the two driving forces that determine the optimal allocation strategy of agricultural water resources.Water supply in irrigated areas usually comes from upstream runoff?or groundwater?,and the demand for water is largely dependent on the reference crop evapotranspiration?ET0?.Both natural conditions and human activities affect the variation of runoff and ET0,resulting in the randomness of water supply and demand.Therefore,it is very important to study the method and model of water resources allocation in irrigation area under the uncertainty of water supply and demand.In this paper,the Jinxi irrigation area in Heilongjiang province is taken as the research object to quantitatively characterize the joint uncertainty of water supply and demand.On this basis,the optimization model of water resources large-scale system in irrigation area is constructed and its solution is discussed,and then the carrying capacity model of agricultural water resources in irrigation area is established to evaluate the optimization results.The main research contents and conclusions are as follows:?1?determine the joint distribution model of runoff and ET0 and the frequency analysis of the occurrence of abundance and drought.The normal distribution,extreme value distribution,distribution,Logistic distribution and Pareto distribution were selected for frequency analysis of runoff and ET0 sequence data.The moment method,maximum likelihood method and maximum entropy principle are used to estimate the parameters of each distribution function.The results of the fitting test show that the distribution combined moment method is the best for the fitting of runoff and ET0.On the basis of determining the runoff and ET0 edge distribution model,six Copula functions were selected as the coupling functions,and the fitting effect of t-copula function was optimal through 2-d joint distribution fitting.The maximum frequency of runoff and ET0 is the same flat combination,the corresponding probability is 29.14%.The probability of co-abundance and co-abundance is 1.51%,and the frequency difference of six co-abundance and co-abundance asynchronous encounters of runoff and ET0 is not obvious.In addition,the frequency of wet-dry synchronous encounter is 32.16%,far less than the wet-dry asynchronous frequency of 67.84%.?2?large-system optimization model of water resources optimization allocation.The model is divided into upper and lower level to simultaneously optimize irrigation water and planting area of each crop at different levels.The first level?field scale?is a single-objective planning model,and the objective function is the maximization of economic benefits.The second level?irrigation area scale?is a multi-objective model.The objective functions are the maximum economic benefit?economic dimension?,the best equity of resource allocation?social dimension?and the minimum greenhouse gas emission?environmental dimension?.Based on the stochastic simulation of water supply and demand,the optimal allocation scheme of water resources under different combinations of supply and demand is explored.The results show that under the nine scenarios of wet-dry combination,the water allocation was between 3.01×108-4.53×108m3,the average water allocation was 3.73×108m3,and the total planting area of the irrigated area was 8.40×104-14.0×104ha.The situation with the highest probability of water supply and demand meeting is the normal-normal combination,the corresponding water allocation was 3.70×108m,which was close to the average water allocation.The total planting area of each crop was 10.91×104ha.The economic benefit value of the irrigated area fluctuates between 13.63×108-22.81×108 yuan.CO2 emissions were 4.19×108-6.95×108kg,CH4 emissions were 6.62×106-11.04×106kg,and N2O emissions were 12.55×106-20.92×106kg.The variation range of Gini coefficient was[0.3899 0.3903],in the degree of relative uniformity.?3?Evaluation of carrying capacity of agricultural water resources.Based on the actual situation of Jinxi irrigation area,an evaluation system of agricultural water resources bearing capacity was constructed,including economic,social and environmental subsystems.Based on the calculation results of the optimization model as the basic data of the index,the index weight was determined by entropy weight method,and the carrying capacity of agricultural water resources was evaluated by TOPSIS model.The evaluation results show that the relative proximity of optimization results of different scenarios is[0.3625,0.6323],and the bearing capacity evaluation of multi-scenario optimization results of irrigated areas is between grade II-IV.Among them,the carrying capacity of the highest level is the normal-dry combination,and the difference between the relative proximity of the wet-dry and dry-dry combination is small,and both are in grade IV. |
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