| The dry and hot valley of the Youjiang River is rich in light and heat,but dry with little rain and high temperature and wind is a typical dry and hot valley.The dry and hot climatic conditions have a great impact on the agricultural production and ecological environment of the region.The use of water is very critical,and the rational use of water resources is not only related to agricultural production,but also to the ecological environment and the sustainable development of the social economy.Tianyang District,located in the middle reaches of the Youjiang Hot Dry Valley,is a region with developed agriculture and abundant agricultural resources.As one of the tropical fruit production bases,accurate estimation of evapotranspiration(ET)in Tianyang District is crucial for agricultural production.Precise estimation of ET provides a scientific basis for irrigation management,facilitates the development of sound agricultural production plans,and enhances crop yield and quality.In this study,the study area is Tianyang District of Baise City,and the Sentinel series satellite image dataset is coupled with the ERA5 meteorological reanalysis data,DEM digital elevation data and land cover classification data to apply the TSEB model to the study area,and the evapotranspiration of the model is expanded in time scale by reference to the evaporation ratio invariance method,so as to estimate the regional evapotranspiration with high spatial and temporal resolution.The spatial and temporal variation characteristics of evapotranspiration under different time scales and the influencing factors were also analyzed.The following conclusions were obtained from this study:(1)The downscaling method DMS was used with fine-resolution(20m)Sentinel-2 remote sensing data to improve the spatial resolution of coarse-resolution(1000m)Sentinel-3 LST data.The resulting residuals showed a bias between-0.20 and 0.33 K,and an RMSD between 1.11 and 3.37 K.This indicates that there is relatively small difference between the full 20m-resolution Sentinel-3 LST data and the coarse-resolution LST data over the study area,which is suitable as an input for the TSEB evapotranspiration estimation model to analyze the temperature state of the soil and vegetation surface.(2)Based on the evapotranspiration estimated by the model and the reference crop evapotranspiration calculated by the FAO Penman-Monteith formula,the reference evapotranspiration ratio was calculated for the corresponding time period,and the actual evapotranspiration was expanded in time scale.The expanded results were verified by comparing with the observed data of vorticity,MOD16 remote sensing evapotranspiration products and actual data of evapotranspiration meter,which showed that the model estimated daily evapotranspiration results were verified with the actual observed values of vorticity with R~2of 0.77 and RMSE of 1.9 mm;the mean absolute error was 0.58 and the mean relative error was 18.07%when compared with the actual data of evapotranspiration meter,which showed that the overall model The estimated evapotranspiration results are reliable and can be applied to the water resources management and agricultural production in Tianyang.(3)The variation patterns of evapotranspiration and energy fluxes for different land cover types in Tianyang district were analyzed at different temporal scales.The daily mean values of net radiation flux and latent heat flux showed an overall ranking order of forestland>shrub>cropland>grassland,while the daily mean value of soil heat flux showed an overall ranking order of grassland>cropland>shrub>forestland.The daily mean value of sensible heat flux showed an overall ranking order of shrub>cropland>forestland>grassland.The overall ranking order of evapotranspiration was forestland>cropland>shrub>grassland,with a seasonal variation trend.It was found that there was a significant linear relationship between surface temperature,vegetation cover,and evapotranspiration,with R~2values of surface temperature and evapotranspiration both exceeding 0.7 and R~2values of vegetation cover and evapotranspiration both exceeding 0.6.However,a complex non-linear relationship existed between elevation and evapotranspiration,with an R~2value of 0.57.This indicates a closer relationship between surface temperature,vegetation cover,and evapotranspiration.Based on the multiple linear regression analysis,it was found that surface temperature and vegetation coverage have a significant impact on evapotranspiration.The significance level of surface temperature is 0.02,with a contribution rate of 45.76%.The significance level of vegetation coverage is 0.00,with a contribution rate of 44.25%.This indicates that surface temperature and vegetation coverage play important roles in the variability of evapotranspiration.On the other hand,the significance level of terrain elevation is 0.14,with a contribution rate of 9.99%,suggesting that its impact on evapotranspiration is relatively small.Surface temperature and vegetation coverage are the primary factors with significant effects on the variation of evapotranspiration,while terrain elevation has a limited influence.These findings can provide scientific basis for agricultural irrigation and water resource management,offering insights for the rational utilization of water resources in Tianyang District.Future research can delve into the mechanisms underlying evapotranspiration and develop more refined models to enhance estimation accuracy. |
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