Remote Sensing of Global Daily Evapotranspiration based on a Surface Energy Balance Method and Reanalysis Data

Xuelong Chen,Yaoming Ma,Zhongbo Su,Isabel Trigo,Pierre Gentine

doi:10.1029/2020jd032873

Abstract

AbstractCurrently available evapotranspiration (ET) products have not provided us with an accurate estimation for global irrigated land area. Thermal energy balance (EB) model has the potential to solve this problem. The accurate estimation of aerodynamic resistances is a major complication in most remote sensing ET models. An EB model using a column canopy‐air turbulent heat diffusion method was developed to more realistically depict dynamic changes in aerodynamic resistance. In order to estimate global ET and land surface fluxes for all weather conditions, Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua and Terra land surface temperature fields were combined and a nearest‐evaporative‐fraction gap‐filling method was merged into the EB model. A global ET product covering the period 2003–2017 was produced using the EB model. By combining thermal and optional information from MODIS satellites and surface meteorological forcing data from ERA‐Interim reanalysis data, the EB model provides a 5 × 5 km resolution estimate of daily ET without spatio‐temporal gaps at the global scale. Assessment of the daily EB ET at 238 flux sites showed a mean bias of 0.05 mm/day and an RMSE of 1.56 mm/day. Analysis of global precipitation minus ET demonstrated that EB ET has a relatively higher potential for agriculture water resource management than currently available global ET products, such as Landflux, GLEAM, MOD16, GLDAS, and ERA‐Interim ET. In addition, the EB model developed in this study can be applied to both polar and geostationary satellite thermal sensors.

Highlights

Evapotranspiration (ET) is the turbulent flux of water vapor from the land surface into the air, including soil evaporation, interception from the canopy, and transpiration through the stomata of plants
In order to estimate global ET and land surface fluxes for all weather conditions, Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua and Terra land surface temperature fields were combined and a nearest-evaporative-fraction gap-filling method was merged into the energy balance (EB) model
The reason for higher ET values from surface energy balance system (SEBS) has been explained in previous publications, which shown that the roughness parameterization method in SEBS tends to produce underestimates of sensible heat flux and overestimates of ET or latent heat flux (Chen, Massman, & Su, 2019; Chen, Su, et al, 2019; Michel et al, 2016)

Summary

Introduction

Evapotranspiration (ET) is the turbulent flux of water vapor from the land surface into the air, including soil evaporation, interception from the canopy, and transpiration through the stomata of plants. ET is modulated by surface turbulence (Su et al, 2001), boundary-layer processes (Kim & Entekhabi, 1998), and biophysics (Verhoef & Egea, 2014). Various ET models that apply different physical process parameterizations have been developed to estimate land surface ET. Different models have resulted in large differences in ET estimation at the continental to global scale (Jiménez et al, 2011; Mueller et al, 2011). Variation among global ET estimates indicate a 50% uncertainty in the annual mean value

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