Study On The Impact Of Evapotranspiration In China On Agricultural Drought

Agricultural drought is difficult to observe directly,and it is feasible and necessary to use other relevant factors for its indirect estimation.The frequent occurrence of drought disasters is closely related to changes in the watershed water balance,and land surface evapotranspiration plays an important role in the watershed water balance.Therefore,the study of the temporal and spatial distribution of land surface evapotranspiration has important application value in the monitoring and early warning of drought disasters.After years of development,the remote sensing evapotranspiration model based on the principle of energy balance has become the mainstream method for accurately estimating evapotranspiration on large-scale non-uniform underlying surfaces.Studying the changing laws of evapotranspiration on different underlying surfaces in China,while assisting other variables,can provide new ideas and methods for agricultural drought monitoring and early warning,and thus improve the ability to respond to agricultural drought disasters.This study modifies the land surface evapotranspiration from MODIS ET model,and analyzes the temporal and spatial changes of land surface evapotranspiration in China.At the same time,it improves the 1949-2018 drought disaster data set and analyzes the distribution characteristics of agricultural drought in China.Then it explores the impact of arable land evapotranspiration on agricultural drought.The main research results are as follows:(1)The simulation accuracy of land surface evapotranspiration based on MODIS ET model in the Chinese study area is high,and the correlation coefficient with the actual evapotranspiration of the station is 0.896,but there is an underestimation.(2)From 2004 to 2010,there was a relatively obvious upward trend in evapotranspiration.After 2010,the overall evapotranspiration did not change much.The evapotranspiration varies greatly between different seasons.The evapotranspiration in summer is higher,followed by spring and autumn,and the evapotranspiration in winter is the smallest.The inter-annual change of evapotranspiration in each season is not obvious.The evapotranspiration first increased and then decreased with the monthly changes.The average monthly evapotranspiration reached its maximum value in July and its minimum value in January.The distribution of evapotranspiration in China is spatially decreasing from southeast to northwest.(3)Agricultural drought disasters in China have the basic characteristics of periodic fluctuation,synchronization of disasters and disasters,and the increasing severity of drought hazards.The correlation coefficient r between the disaster rate and the disaster rate is 0.858.Drought disasters occur in turns,usually with a high disaster rate.The proportion of years with extremely severe and severe droughts is large.The occurrence of drought has spatial characteristics,showing a pattern of "North is more serious than South,while Central and Eastern is more serious than Western".Among the northern regions,Shandong has the highest disaster rate.Among the southern regions,Sichuan has the highest disaster rate.Nationwide,Tibet is the least affected.(4)From 2001 to 2018,the annual total evapotranspiration of cropland in China showed a slight increase,with large fluctuations.The trend of the annual average evapotranspiration of cropland is consistent with the total annual evapotranspiration of cropland.The average annual evapotranspiration of cropland in China shows a declining distribution pattern from Southeast to Northwest.Among the five major grain producing areas,the average annual evapotranspiration is the largest in the middle reaches of the Yangtze River and the Jianghuai area,followed by the Sichuan Basin and the Huang-Huai-Hai Plain,and the relative average annual evapotranspiration is the smallest in the Sanjiang Plain and the Songnen Plain.(5)In the middle reaches of the Yangtze River and the Jianghuai area,the Sichuan Basin,there is a strong correlation between evapotranspiration and drought disasters,with correlation coefficients of 0.627 and 0.567,respectively.This indicates that the amount of evapotranspiration is high,and the affected area is correspondingly large.Therefore,using evapotranspiration to monitor drought disasters can obtain better results.However,in the Sanjiang Plain and the Songnen Plain,the correlation between the two is not significant.