Study On Surface Evapotranspiration In The Sihe River Basin Based On ERA5 Remote Sensing Data

In this study,the daily potential evapotranspiration（ET₀）of each station was calculated based on the daily meteorological observation data of the Sihe River Basin and its neighboring weather stations,based on the ERA5 long sequence remote sensing data from1960 to 2020,the actual evapotranspiration（ET_a）was calculated by the Penman-Monteith model based on the remote sensing leaf area index,and the spatiotemporal variation characteristics of ET₀ and ET_a were analyzed by linear tendency estimation,trend testing and spatial interpolation.The sensitivity of ET₀ and ET_a to each factor was quantitatively studied,and the contribution of each factor to the change of ET₀ and ET_a was quantitatively identified based on the contribution rate.The results show that:1)the number of sunshine hours,wind speed and precipitation in the Sihe River Basin from 1960 to 2020 showed a downward trend,and the average temperature and relative humidity showed an upward trend.ERA5 remote sensing meteorological factors showed an upward trend of 2 m dew point temperature and 2 m temperature,net radiation and Atmospheric pressure showed a downward trend,and the interannual variation of LAI was not obvious.2)The average ET₀ value in the Sihe River Basin in the past 60 years was 933mm,showing a downward trend,and there was a mutation point in 1977.In summer,June accounts for the highest proportion of evapotranspiration throughout the year.The spatial trend of ET₀ is high in the west and low in the east.Annual ET₀ is the most sensitive to sunshine hours,followed by relative humidity,spring and summer ET₀ is the most sensitive to sunshine hours,autumn and winter are the most sensitive to relative humidity,sunshine hours contribute the most to ET₀ changes,followed by relative humidity.3)The annual average value of ET_a in the Sihe River Basin from 1960 to 2020 was631.10mm,soil evaporation accounted for 30.18%,vegetation transpiration accounted for69.82%,and the proportion of ET_a in the basin was 68%;In the past 60 years,the average annual ET_a showed an upward trend,there were mutation points in 1991,summer and spring were the main evapotranspiration seasons,and the ET_a in each season showed an upward trend,and the spatial distribution pattern of ET_a from 1960 to 2020 did not change significantly.The annual ET_a in the Sihe River Basin was the most sensitive to net radiation and Atmospheric pressure,the spring,autumn and winter ET_a was the most sensitive to net radiation and Atmospheric pressure,the summer ET_a was the most sensitive to net radiation and 2 m dew point temperature,and the factors that contributed the most to the annual ET_achange were net radiation and Atmospheric pressure.The average annual ET_a in the Sihe River Basin was closely related to land use type,with the highest annual ET_a in farmland and forest and grassland,626-634mm·a^-1,and the urban and bare land ET_a being smaller,562mm·a^-1 and 559mm·a^-1,respectively,and the ET_a of all land use types showed an upward trend in the past 60 years.This study provides a basic reference for the research on the impact of water cycle on water cycle,optimal allocation of water resources and agricultural irrigation management under the changing environment of the Sihe River Basin.