Varying performance of eight evapotranspiration products with aridity and vegetation greenness across the globe

Abstract

The wide application of the evapotranspiration (ET) products has deepened our understanding of the water, energy and carbon cycles, driving increased interest in regional and global assessments of their performance. However, evaluating ET products at a global scale with varying levels of dryness and vegetation greenness poses challenges due to a relative lack of reference data and potential water imbalance. Here, we evaluated the performance of eight state-of-the-art ET products derived from remote sensing, Land Surface Models, and machine learning methods. Specifically, we assessed their ability to capture ET magnitude, variability, and trend, using 1,381 global watershed water balance ET as a baseline. Furthermore, we created aridity and vegetation categories to investigate performance differences among products under varying environmental conditions. Our results demonstrate that the spatial and temporal performances of the ET products were strongly affected by aridity and vegetation greenness. The poorer performances, such as underestimation of interannual variability and misjudged trend, tend to occur in abundant humidity and vegetation. Our findings emphasize the significance of considering aridity and vegetation greenness into ET product generation, especially in the context of ongoing global warming and greening. Which hopefully will contribute to the directional optimizations and effective applications of ET simulations.

Large Divergence of Satellite Monitoring of Diffuse Radiation Effect on Ecosystem Water‐Use Efficiency

“…The results showed that diffuse radiation is more efficient than direct radiation in promoting the ET. This mainly because the increase in LUE, which can enhance the plant transpiration through their coupling in leaf stomata (B. Wang et al., 2023; H. Wang et al., 2023). Of course, the more uniform distribution of radiation induced by diffuse radiation also enhances the ETE (Chakraborty et al., 2021).…”

“…To acquire the high‐quality data, the ground‐based data must meet the flowing criteria: corresponding QC data≥0.8; no precipitation. To investigate the response of vegetation to diffuse radiation, we only analyze the data during the growing seasons, which are mainly distributed to May‐September in the Northern Hemisphere and September‐March in the Southern Hemisphere (B. Wang et al., 2023; H. Wang et al., 2023).…”

“…Gound‐based eddy covariance flux tower sites are commonly used to investigate the factors that influence WUE, such as diffuse radiation (B. Wang et al., 2023; H. Wang et al., 2023) and carbon dioxide (Keenan et al., 2013). However, the number of ground‐based sites is very limited.…”

“…Changes of cloud and aerosols will affect the radiation received by the plant by decreasing the total radiation and increasing the fraction of diffuse radiation (Zhang et al., 2021, 2023). Diffuse radiation may also interact with other environmental factors, such as temperature, precipitation and VPD, to modulate WUE (B. Wang et al., 2021; X. Wang et al., 2021; M. Wang et al., 2021; B. Wang et al., 2023; H. Wang et al., 2023).…”

“…However, the increase in diffuse radiation usually accompanied with the decrease total radiation, which can reduce plant transpiration (Zhang et al., 2021). Therefore, diffuse radiation has stronger fertilization effects on GPP than ET (B. Wang et al., 2023; H. Wang et al., 2023).…”