Estimation of Evapotranspiration and Its Components across China Based on a Modified Priestley–Taylor Algorithm Using Monthly Multi-Layer Soil Moisture Data

Wanqiu Xing,Linye Song,Weiguang Wang,Mingzhu Cao,Quanxi Shao

doi:10.3390/rs13163118

Abstract

Although soil moisture (SM) is an important constraint factor of evapotranspiration (ET), the majority of the satellite-driven ET models do not include SM observations, especially the SM at different depths, since its spatial and temporal distribution is difficult to obtain. Based on monthly three-layer SM data at a 0.25° spatial resolution determined from multi-sources, we updated the original Priestley Taylor–Jet Propulsion Laboratory (PT-JPL) algorithm to the Priestley Taylor–Soil Moisture Evapotranspiration (PT-SM ET) algorithm by incorporating SM control into soil evaporation (Es) and canopy transpiration (T). Both algorithms were evaluated using 17 eddy covariance towers across different biomes of China. The PT-SM ET model shows increased R2, NSE and reduced RMSE, Bias, with more improvements occurring in water-limited regions. SM incorporation into T enhanced ET estimates by increasing R2 and NSE by 4% and 18%, respectively, and RMSE and Bias were respectively reduced by 34% and 7 mm. Moreover, we applied the two ET algorithms to the whole of China and found larger increases in T and Es in the central, northeastern, and southern regions of China when using the PT-SM algorithm compared with the original algorithm. Additionally, the estimated mean annual ET increased from the northwest to the southeast. The SM constraint resulted in higher transpiration estimate and lower evaporation estimate. Es was greatest in the northwest arid region, interception was a large fraction in some rainforests, and T was dominant in most other regions. Further improvements in the estimation of ET components at high spatial and temporal resolution are likely to lead to a better understanding of the water movement through the soil–plant–atmosphere continuum.

Highlights

Understanding water and heat exchange information of the soil–plant–atmosphere continuum (SPAC) is imperative to better manage more restricted water resources in the future
To evaluate the influences of plant access on atmospheric demand and of deeper water storage intensification or mitigating vegetation sensitivity on water availability, the transpiration response curve to soil water availability can be drawn, and the results indicate that higher canopy heights show less sensitivity to soil water availability [24,42]
soil moisture (SM) data collected at three observational networks (i.e., Ngari, Maqu, and Naqu; detailed information can be found in Yang et al (2020)) across the Tibetan Plateau were employed to validate the reconstructed SM dataset [49]

Summary

Introduction

Understanding water and heat exchange information of the soil–plant–atmosphere continuum (SPAC) is imperative to better manage more restricted water resources in the future. As one of the most important connecting terms in SPAC [1], evapotranspiration (ET), which consists of evaporation from wet surfaces (E) and transpiration through plants (T), is critical for both the energy budget and water balance in the earth–atmospheric system. ET partitioning is of prime importance for the water resources and forests management. Over the past five decades, much effort has been devoted to the development of techniques and algorithms for ET or its components estimation, as documented by a substantial body of literatures [4,5,6,7]. Estimates of ET or its components are still a major challenge for the complex climatic and underlying conditions

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