Study On Medium And Long Term Irrigation Water Demand Forecast Of Rice In South China

Rice is planted in a large area in southern China,and the irrigation water consumption is large.The annual and inter-annual distribution of precipitation is not balanced among regions.In addition,factors such as the South-to-North Water Transfer Project and the increase of the proportion of non-agricultural water aggravate the contradiction between supply and demand of agricultural irrigation.As the essential basic data of river basin planning,water resource distribution,water conservancy project design and irrigation management,rice irrigation water demand has important practical guiding significance for the research of rice irrigation water demand measurement and report.At present,the prediction of irrigation water demand is mainly based on short-term forecast,which is difficult to meet the requirements of medium-and long-term irrigation water distribution management.Taking rice in Gaoyou Irirrigation Area of Jiangsu Province as the research object,this paper studied the variation trend of rice water demand by using meteorological data from1980 to 2019,determined the main controlling factors affecting the evapotranspiration of reference crops by using sensitivity analysis method,and combined with the mid-range and long-term meteorological forecast data from 2018 to 2019.A forecast method of reference crop evapotranspiration based on the correction of main control factor was proposed,and then the medium and long term irrigation water requirement of rice in southern China was predicted.The main research conclusions are as follows:（1）The average annual water requirement of rice crops in Gaoyou was 534.45mm,and increased at a rate of 20.2mm/10a.The average annual irrigation water requirement is492.69mm,which increases at a rate of 20mm/10a.The average annual irrigation water requirement of Gaoyou rice at jointing and booting stage and heading and flowering stage was the largest,accounting for 58.5%of the irrigation water requirement in rice growth stage.（2）With water balance method to obtain rice reproductive period of effective rainfall as the evaluation standard,respectively for the USDA-SCS method,USDA-SCS correction method,the USDA ratio method and correlation analysis method to calculate the effective rainfall and precision evaluation,the results show that the USDA-SCS correction method to calculate effective rainfall highest precision,the consistency index d is 0.87,the relative error RE just 0.18.（3）Amount of main meteorological factors on reference crop evapotranspiration is sensitive to the daily average ET₀ coefficient order from big to small order is the highest temperature,sunshine time,wind speed,the lowest temperature,climatic factors change on the average contribution of ET₀ quantity order from big to small order is the highest temperature,wind speed,the lowest temperature,sunshine time,show that the highest temperature is the main controlling factor of reference crop evapotranspiration quantity change.（4）The prediction data of the maximum temperature of the main control factor are corrected by using the linear regression equation with one variable and the decreasing average method.After the correction,the RMSE and the MAE are decreased,while the regression coefficient b and the consistency index d are increased.From the overall point of view,the correction effect of the decreasing average method is better than that of the linear fitting method with one variable.（5）Compared with other models,the accuracy of the proposed PT model is significantly improved,with the root mean square error of 12.50mm,the mean absolute error of 5.89mm and the consistency index of 0.93.Based on the recommended forecast model of monthly reference crop evapotranspiration,the monthly irrigation water requirement of rice was predicted.The root mean square error and consistency index of the forecast were 49.92mm and 0.86,which could meet the accuracy requirement of medium and long term irrigation water requirement of rice.