Evapotranspiration Characteristics Of Summer Maize And Optimization Of Reference Crop Evapotranspiration Model

Reference crop evapotranspiration is an important indicator for farmland drought and soil moisture detection.ft is necessary to study the variation law of farmland evapotranspiration and the meteorological factors affecting it,as well as the optimization of reference crop estimation model for agricultural water resources management and regulation of annual water management.This is also one of the important concerns of our government departments in implementing sustainable development strategies.In this study,the summer maize experiment in the Xinmaqiao experiment area was used as a practical case in the central region of the Yangtze River and Huaihe River.The data includes meteorological data and measured evapotranspiration data from large-scale weighing lysimeter.We used a variety of methods to analyze the variation of evapotranspiration during the growth period of summer maize in this region and its correlation with various meteorological factors.Using the surface meteorological data and radiation data of Hefei,Nanjing,Hangzhou and Wuhan,we screened the estimation model of net long-wave radiation which is most suitable for the central region of the Yangtze River and Huaihe River.At the same time,we re-evaluated the empirical parameters of the Angstrom model and improved accuracy of the Penman-Monteith model in this area.The main conclusions are as follows:(1)The change of daily evapotranspiration of summer maize on sunny days and cloudy days first rises and then decreases.The amount of evapotranspiration on a sunny day is much higher than that on a cloudy day.The trend of evapotranspiration of summer maize during the whole growth period first increased and then decreased.The increase in seedling stage is small,and its peak appears in the jointing stage,theanthesis stage,and the silking stage.The evapotranspiration during grain filling and maturity is generally declining,with small fluctuations.The difference between the crop evapotranspiration estimated by the Penman-Monteith model and the measured value is large or small.As different weather conditions have a greater impact on the amount of solar radiation reaching the ground,the difference between the actual evapotranspiration and the estimated value increases and decreases:When the estimated value of the P-M model is higher than the measured value,the corresponding weather is continuous rainy weather;when the measured value is higher than the estimated value,it is basically continuous sunny day with few clouds;when the difference between the simulated value and the measured value is small,the weather is usually cloudy.Among the six meteorological factors of average temperature,sunshine hours,relative humidity,wind speed,solar radiation and actual vapor pressure,the most relevant meteorological factor with evapotranspiration is solar radiation,and the lowest correlation is wind speed.(2)The net short-wave radiation in the central region of the Yangtze River and Huaihe River.showed a trend of a slight decline after a significant decline in the past 20 years.The total amount and average daily amount of net short-wave exposure are as follows:summer>spring>autumn>winter.The range of change from large to small is spring>autumn>summer>winter.The monthly mean value is consistent with the corresponding seasonal mean value.The net long-wave radiation exposure in the central part of the Yangtze River and Huaihe River showed a significant downward trend in 20 years.The order of total and average from spring to winter was as follows:spring>winter>autumn>summer.In other words,the seasonal total amount of net long-wave radiation in this region is not completely positively correlated with the total amount of solar radiation.The amplitude of the net long-wave radiation is as follows:spring>autumn>winter>summer.(3)Among the six net long-wave radiation estimation models,the performance of the Penman model is optimal,indicating that this is the most suitable model for the central part of the Yangtze River.The difference between the estimated and measured values of the six estimation models shows that the simulation accuracy of the autumn and winter seasons is significantly higher than the spring and summer seasons.(4)After various correlations and error verifications,it is found that the e:mpirical parameters in the Angstrom model determined by genetic algorithm and least squares method effectively improve the estimation accuracy of the FAO Penman-Monteith model.The accuracy of the genetic algorithm is slightly higher than the least squares method.The empirical parameters of the Angstrom model in the central part of the Yangtze River are:a?0.2408,b=0.4419;The sensitivity of the empirical parameters indicates that the results of the two calibration methods are better in the FAO Penman-Monteith model,and the sensitivity of the empirical parameter b is significantly higher than the empirical parameter a.