Simplified Priestley–Taylor Model to Estimate Land-Surface Latent Heat of Evapotranspiration from Incident Shortwave Radiation, Satellite Vegetation Index, and Air Relative Humidity

Yunjun Yao,Zhiqiang Xiao,Zijing Xie,Zhenhua Di,Ruiyang Yu,Kun Jia,Junming Yang,Xiaozheng Guo,Xiangyi Bei,Xiaotong Zhang,Ke Shang

doi:10.3390/rs13050902

Abstract

An operational and accurate model for estimating global or regional terrestrial latent heat of evapotranspiration (ET) across different land-cover types from satellite data is crucial. Here, a simplified Priestley–Taylor (SPT) model was developed without surface net radiation (Rn) by combining incident shortwave radiation (Rs), satellite vegetation index, and air relative humidity (RH). Ground-measured ET for 2000–2009 collected by 100 global FLUXNET eddy covariance (EC) sites was used to calibrate and evaluate the SPT model. A series of cross-validations demonstrated the reasonable performance of the SPT model to estimate seasonal and spatial ET variability. The coefficients of determination (R2) of the estimated versus observed daily (monthly) ET ranged from 0.42 (0.58) (p < 0.01) at shrubland (SHR) flux sites to 0.81 (0.86) (p < 0.01) at evergreen broadleaf forest (EBF) flux sites. The SPT model was applied to estimate agricultural ET at high spatial resolution (16 m) from Chinese Gaofen (GF)-1 data and monitor long-term (1982–2018) ET variations in the Three-River Headwaters Region (TRHR) of mainland China using the Global LAnd-Surface Satellite (GLASS) normalized difference vegetation index (NDVI) product. The proposed SPT model without Rn provides an alternative model for estimating regional terrestrial ET across different land-cover types.

Highlights

Latent heat of evapotranspiration (ET) observations and simulations are crucial in monitoring the energy and water cycle among different land-surface ecosystems [1,2,3,4].Especially in typical eco-environmentally vulnerable areas, ET is affected by serious surface dry status resulting in a food and water resources crisis as well as eco-environment deterioration [5,6,7,8]
In the simplified Priestley–Taylor (SPT) model, the ET is calculated as: ET = ∂f(c) where ∂ refers to PT parameter under wet surface conditions (1.26); ∆ refers to the slope for saturated vapor pressure (SVP) curve; γ stands for psychrometric constant. f(c) is the environmental constraint that is determined by meteorological and satellite variables [10,22]
Tmin represents the effects of temperature on evaporation fraction (EF), normalized difference vegetation index (NDVI) characterizes the vegetation transpiration influenced by temperature and water, and relative humidity (RH) takes into account the contribution of SM on EF for a short period

Summary

Introduction

Latent heat of evapotranspiration (ET) observations and simulations are crucial in monitoring the energy and water cycle among different land-surface ecosystems [1,2,3,4].Especially in typical eco-environmentally vulnerable areas, ET is affected by serious surface dry status resulting in a food and water resources crisis as well as eco-environment deterioration [5,6,7,8]. Satellite remote sensing is the most important approach for acquiring regional water fluxes because it has improved regional-scale estimates of land-surface parameters linked to ET (e.g., surface net radiation, Rn; leaf area index, LAI; normalized difference vegetation index, NDVI; soil moisture, SM; land-cover types and albedo) [10,11,12]. Over the past 40 years, many satellite-derived ET approaches have been developed to simulate regional water fluxes [13,14,15,16,17,18,19].

Methods

Results

Discussion

Conclusion