| The evolution law of dynamic drought characteristics in each growth stage of crops,the distribution characteristics of planting structure and canal system in irrigation area should be considered in water resources allocation in irrigation area.The uncertainty of water inflow,the complexity of comprehensive benefits and the timeliness of water resources allocation also have a direct impact on the efficiency of water resources allocation in irrigation area.Considering the uncertainty of the influencing factors of water resources allocation in irrigation areas and the timeliness of water resources allocation,real-time allocation of water resources in irrigation areas is an important measure for China to build water-saving,ecological and sustainable agriculture.This paper takes Sanliuzhai Yellow River irrigation area as the research object.Firstly,the SWAT model embedded real-time irrigation simulation module was used to study the dynamic drought characteristics of crops,and the drought frequency and drought intensity of crops in different growth stages were identified.Secondly,the model of planting structure optimization and adjustment in irrigation area was established,and the mechanism of planting structure adjustment on water use efficiency and crop carbon flux in irrigation area was analyzed.Thirdly,an optimal allocation model of water resources in irrigation area is constructed.The robust optimization method of nested double optimization process and the beetle antennae search algorithm are used to solve the model respectively.The driving factors of efficient utilization of water resources in irrigation area under the influence of complex uncertain factors are explored,which provides a variety of feasible schemes for optimal allocation of water resources in irrigation area.Finally,an optimal allocation model of real-time water resources in irrigation area is established,and the function of real-time water resources allocation on the utilization efficiency of water resources in irrigation area is determined to realize the real-time and dynamic regulation of water resources in irrigation area.The main research results are as follows:1.The dynamic characteristics and development law of drought in each growth stage of crops in irrigation area were revealed.In view of the lack of attention to real-time response in the existing research on crop drought characteristics,a real-time irrigation simulation model calculation program was developed.The program was called when the SWAT model was used to simulate the soil moisture content during the study period,so as to accurately simulate the real-time dynamic change process of soil moisture content in the study area,and then the crop dynamic drought characteristics evaluation model with real-time soil relative humidity as the evaluation index was established to evaluate the crop dynamic drought characteristics in the study area.The drought of winter wheat and summer maize in the irrigation area from 1972 to 2017 was mainly affected by precipitation.The dynamic change trend of drought in the growth period was consistent with the dynamic change trend of precipitation,showing the characteristics of large interannual variation but stable multi-year change trend.Drought was prone to occur in each growth stage of winter wheat,and the frequency of drought was more than 84.8%.The highest frequency of drought was 95.7%from flowering stage to maturity stage.The drought was mainly moderate drought,and the frequency of mild drought and severe drought was similar,with occasional extreme drought.Summer maize was prone to drought during sowing-emergence stage and emergence-jointing stage,and the frequency of drought was 84.8% and 78.3%,respectively.Drought in each growth stage was mainly moderate drought,occasionally special drought,and the frequency of severe drought was extremely low.2.The response relationship between canal leakage and crop net carbon absorption to planting structure adjustment was analyzed.In order to solve the problem of insufficient calculation accuracy of canal leakage in irrigation area,a multiple regression model of real-time leakage velocity of canal system was established to accurately calculate the real-time leakage of canal system in irrigation area.Furthermore,an optimal adjustment model of planting structure in irrigation area was established with the minimum leakage of canal system and the maximum net carbon absorption as the objective function,so as to realize the planting structure adjustment mode with the controlled irrigation area of canal system as the optimization unit and the crop growth period as the optimization cycle.The optimized adjustment model of planting structure can effectively reduce the leakage of canal system and increase the net carbon absorption of crops in irrigation area.Under different planting structure adjustment schemes,the planting area of summer maize showed different degrees of increase,the planting area of economic crops in summer showed different degrees of decrease,the planting area of winter wheat showed a decreasing trend,and the planting area of economic crops in winter showed an increasing trend.Under each scheme,the leakage of most canal systems in the irrigation area decreased to varying degrees,and the net carbon absorption increased to varying degrees.Under the optimal adjustment scheme,the water use efficiency of the irrigation area increased by about 16.03%,and the net carbon absorption of crops increased by about 2.18%.3.The mechanism of the real-time allocation of water resources in the irrigation area on the comprehensive benefits of the irrigation area is revealed.Aiming at the problem that the uncertainty of the weight value of the objective function in the multi-objective optimal allocation of water resources in the existing irrigation area cannot be quantitatively expressed and cannot meet the real-time irrigation decision-making,the double optimization process is nested in the robust optimization model to solve the real-time optimal allocation model of water resources in the irrigation area coupled with the real-time simulation of insufficient irrigation,and the real-time optimal allocation of water resources in the irrigation area under the influence of complex factors is realized.The real-time allocation model of water resources in irrigation area based on robust optimization method provides a variety of feasible schemes for water resources allocation in irrigation area under the influence of uncertain factors.The water saving effect of water resources allocation scheme in irrigation area is better,and the water saving ratio is between 5.12% and 18.2%.Compared with the traditional allocation scheme,the total water allocation amount of the real-time allocation scheme of water resources in the irrigation area is reduced by 14.97%,and the water production efficiency and ecological benefit are increased by 5.22% and 13.64% respectively.The comprehensive benefit of the irrigation area under the real-time allocation scheme is obviously improved.Based on the water resources allocation scheme of irrigation area,the crop planting experiment was carried out.The measured values of each objective function under different experimental schemes were consistent with the simulated values,and the timeliness and accuracy of the real-time water resources allocation scheme were better. |
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