Prediction And Analysis Of Regional Crop Water Demand Based On CMIP6 Optimal Pattern Set By Machine Learning

In the context of global climate change,the shortage of water resources is increasing.Zhongwei City is one of the regions with serious shortage of water resources in Ningxia.The water for economic and social development mainly depends on the limited allocation of the Yellow River water resources.In recent years,with the intensification of extreme climate,the trend of water resources shortage in Zhongwei City is increasing.Agriculture is the main water sector in the study area,and climate change will have a strong impact on agricultural water use in the future.Therefore,it is of great significance to clarify the response law of crop water demand to climate change in Zhongwei City in the future for the formulation of regional agricultural policies and the rational allocation of regional agricultural water resources.This paper takes the main grain crops in Zhongwei City as the research object,evaluates the changes and impacts of crop water demand in the study area under future climate change,and discusses the impacts of different meteorological factors on crop water demand changes,with a view to providing scientific guidance for agricultural production and scientific management of water resources in the study area.The main research results are as follows:(1)Using multiple machine learning stacking methods(Stacking)and multiple mode sets(MME)to accurately model climate variables.The results show that compared with the original GCM,the Stacking model improves the accuracy of simulated precipitation depth and solar radiation by 65.6%and 16.18%respectively,while the minimum and maximum temperatures increase by 24.21%and 37.37%respectively.The simulation accuracy of average wind speed and relative humidity is 33.85%and 36.93%higher than that of the original GCM.Therefore,the Stacking model can be used as an effective method to improve the accuracy of climate variable downscaling in the region.The performance of the StackingME model in simulating the minimum temperature(Tmin),maximum temperature(Tmax),solar radiation(Rs),relative humidity(Hurs),average wind speed(Wind)and rainfall(Pr)is more accurate than other single models,and the simulation effect is improved.(2)Based on the simulated climate change data under the moderate intensity carbon emission control scenario(SSP245)and the high intensity carbon emission control scenario(SSP585),the crop water requirements of six main crops were calculated.The results showed that the climate variables of the main crops in the region showed different rates of increase or decrease during the growth period,and the SSP585 scenario was more significant than the SSP245 scenario.The crop water requirement(ETc)of rice ranks first among the six crops,with 948 mm and 982 mm under the SSP245 and SSP585 scenarios,respectively.The ETc of winter wheat,corn,soybean,potato and spring wheat decreased in turn.Spring wheat has the lowest ETc,which is 501.61mm and 514.13 mm under the SSP245 and SSP585 scenarios,respectively,only about 52%of that of rice.The ETc of the six crops has the same time trend as ET0,which means that the ETc of the future will increase with the passage of time,and the increment under the SSP585 scenario will be more obvious.(3)The influence of meteorological factor disturbance on ETc is discussed by using sensitivity coefficient and contribution rate.The results showed that the most influential climatic factors on the reference crop water demand in the study area were relative humidity,maximum temperature,solar radiation,average wind speed,and minimum temperature.Among several crops,potato is the most affected by the changes of relative humidity,minimum temperature and solar radiation,and soybean is the most affected by the changes of maximum temperature and average wind speed.The changes of minimum temperature,maximum temperature and solar radiation have the smallest impact on the water demand of winter wheat reference crops,the changes of relative humidity have the smallest impact on the water demand of spring wheat reference crops,and the changes of average wind speed have the smallest impact on the water demand of potato reference crops.The reference crop water demand of the six main crops in the study area is mainly affected by the change of relative humidity,and potato,soybean,rice and corn are more affected by the change of relative humidity in the later stage of the growth period,while spring wheat is more vulnerable to the change of relative humidity in the early stage of the growth period,and winter wheat is more vulnerable to the change of relative humidity in the early and middle and late stages of the growth period.In the future two climate scenarios,The temperature shows an increasing trend,which is also the main reason for the increase of reference water demand of crops.