Study On Monthly Scale Irrigation Water Requirement Of Wheat-Maize Rotation In North China

The traditional water resources evaluation takes the year as the scale,but it is difficult to support the demand of water resources refined management in timeliness.With the deepening of the impact of human activities on the natural water cycle and the aggravation of the water crisis,the requirements for the timeliness and accuracy of water resources continue to increase in order to ensure the sustainable development and utilization of water resources,and it is urgent to carry out relevant technical research such as monthly water resources assessment.As the largest water user,the research on the monthly water consumption rule and forecast of agricultural water consumption is particularly critical.The study on monthly-scale irrigation water requirements of wheat-maize rotation in North China provides useful reference for monthly-scale agricultural water evaluation and management.Taking Daxing District of Beijing as the research area and wheat-maize rotation as the research object,using the meteorological data of 1959-2018 and the measured data of irrigation test station,this paper puts forward the calculation model of suitable effective precipitation of wheat-maize rotation.The trend of wheat-maize rotation irrigation water requirement in different time series was analyzed with the M-K trend test method.At the same time,the weather forecast was used to forecast the monthly irrigation water requirement of wheat-maize rotation.The main conclusions are as follows:(1)The validated AquaCrop model is used to obtain the effective precipitation of wheat-maize rotation as an evaluation standard.The simulation results using ratio method,USDA method,USDA-SCS method and USDA-SCS correction method are compared and analyzed.The results show that the modified USDA-SCS correction method is better for winter wheat to simulate the overall trend,while the USDA-SCS correction method is better for summer maize to simulate the effective precipitation.(2)The irrigation water requirement of wheat-maize rotation in North China increased at the rate of 2.88mm/10a and 21.02mm/10a in the past 60a and 30a,respectively.Analysis of the changes in irrigation water requirement in different time series can prevent the long-term series from having a balanced effect on the rapid changes in the short and medium term.It is beneficial to better grasp the impact of short and medium term climate change on crop irrigation water requirement,and has important reference significance for future water resources planning.(3)The main influencing factors of irrigation water requirement in wheat-maize rotation growth period were obtained by correlation analysis.The key meteorological factors affecting the irrigation water requirement of winter wheat were relative humidity,VPD(Vapor Pressure Deficit)and sunshine hours,negatively correlated with relative humidity and positively correlated with VPD and sunshine hours,all reached extremely significant correlation levels.The key meteorological factors affecting the irrigation water requirement of summer maize were VPD,maximum temperature and relative humidity,which were negatively correlated with relative humidity and positively correlated with VPD and maximum temperature,all reached significant levels.(4)Through numerical analysis of weather forecast data obtained by China Weather Network,PT-MC combination model for monthly scale reference crop evapotranspiration forecasting in North China was constructed.The simulation determination coefficient and consistency index were both greater than 0.90,and the regression coefficient was close to 1,the RMSE was less than 11.20mm,which achieved accurate forecast of monthly reference crop evapotranspiration.At the same time,the newly constructed effective precipitation calculation model,monthly scale reference evapotranspiration combined estimation model,and analytical data of medium and long term precipitation forecast were used to forecast the monthly scale irrigation water requirement for wheat-maize rotation in North China.The MAE was 17.42mm,the RMSE was 26.18mm,the R~2 was 0.57,and the consistency index was 0.87,which can meet the requirements for the precision of irrigation water requirement forecasting on monthly scale for wheat-maize rotation in North China.The results in this paper can provide theoretical basis for agricultural water distribution management and monthly forecast of agricultural water use in North China.