Water Content Of Winter Wheat In The Upper Reaches Of Huaihe River Based On SEBAL Model Productivity Estimation

The upper reaches of the Huaihe River have sufficient water and heat and are suitable for the growth of agricultural crops.However,droughts and floods occur frequently in the basin,the spatial distribution of precipitation is not balanced,and it is difficult to coordinate the matching of crop water demand and water supply.Therefore,studying the contradiction between water supply and demand in this region is of great significance.How to improve the water use efficiency in the upper reaches of the Huai River,increase the water productivity of winter wheat,and reduce the use of water resources while ensuring the increase in winter wheat yields,has become an important breakthrough in solving the shortage of agricultural irrigation water in the upper reaches of the Huaihe River and promoting the steady and high yield of winter wheat.Based on the 2013-2018Landsat-8 remote sensing image data and the daily data of 8 meteorological stations,this study uses the SEBAL model to simulate daily surface evapotranspiration in the upper reaches of the Huaihe River,and uses four evapotranspiration formulas:PM method,IA method,Tu method and JH method Method to conduct comparative analysis,explore the temporal and spatial characteristics of evapotranspiration,then analyze the changes of daily evapotranspiration,groundwater depth and soil type,and finally analyze the temporal and spatial changes of water productivity in the main winter wheat producing areas in the upper reaches of the Huaihe River.The main conclusions are as follows:（1）SEBAL model evapotranspiration comparison and spatiotemporal variation characteristic analysis:evapotranspiration comparison,the daily-scale surface evapotranspiration estimated by the SEBAL model is within a reasonable range with the PM method and other four evapotranspiration calculation methods.The errors are all less than 10%,indicating that the SEBAL model has good accuracy in simulating the evapotranspiration in the upper reaches of the Huaihe River.Temporal and spatial distribution characteristics of daily evapotranspiration:In terms of time,areas with high evapotranspiration are concentrated in the season of vigorous vegetation growth.In space,the evapotranspiration in the western mountainous areas and residential areas is high in all seasons;the evapotranspiration in different seasons of the crop planting areas in the central plain fluctuates greatly with changes in crop growth;the southern mountainous areas have complex terrain,high vegetation coverage,and river networks.Many,evapotranspiration varies most in different seasons.In addition,the slope and aspect of the southern mountainous area have a significant impact on the evapotranspiration,and there is a general trend that the evapotranspiration on the southern slope is greater than that on the northern slope.（2）Analysis of the relationship between evapotranspiration,underlying surface factors,and atmospheric environment:From the perspective of groundwater burial depth,evapotranspiration appears as a bedrock mountain area>3-5 m>1-3m buried depth area.The evapotranspiration of the three groundwater burial depths has a high concentration area of 1.54-1.64 mm/d,and the evapotranspiration ratio is between 190‰-456‰;the evapotranspiration of a low concentration area is 1.44-1.54 mm/d Among them,evapotranspiration accounts for less than 190‰.In terms of soil types,the proportion of the highest daily evapotranspiration of the five soil types is anthropogenic soil>lakes and reservoirs>semi-hydrated soil>leached soil>primary soil.However,the proportion of evapotranspiration of the five soil types is between 1.62-1.68 mm/d,and the difference in daily evapotranspiration of different soil textures is not significant.In terms of elevation and atmospheric environment,elevation and evapotranspiration are extremely significantly positively correlated（P=0.472）,and evapotranspiration is most active when the altitude is 25-200 m;surface temperature and evapotranspiration are significantly positively correlated（P=0.223）,And the evapotranspiration is most active when the temperature is 14-24℃;the correlation between the atmospheric external reflectance and the surface albedo and the evapotranspiration is weak.（3）Temporal and spatial variation characteristics of water productivity in the main winter wheat production areas:From 2013 to 2016,the water productivity of winter wheat in Pingyu County,Runan County,Xi County and Zhengyang County were respectively:0.13-0.93 kg·m^-3,0.10-0.57kg·m^-3,0.09-0.46 kg·m^-3 and 0.12-0.51 kg·m^-3.The spatial difference in the water productivity of winter wheat is gradually shrinking,and the water productivity of winter wheat at the county scale is gradually developing towards a balanced development.The significance of the effectiveness of human intervention has become one of the important factors affecting the water productivity of the parcel unit.