Soil Moisture and Atmospheric Aridity Impact Spatio‐Temporal Changes in Evapotranspiration at a Global Scale. Issue 8 (14th April 2023)

• Record Type: Journal Article
• Authors: Zhang, Wenmin; Koch, Julian; Wei, Fangli; Zeng, Zhenzhong; Fang, Zhongxiang; Fensholt, Rasmus
• Is Part Of: Journal of geophysical research. Volume 128:Issue 8(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2023-04-14
• Subjects: Atmospheric physics -- Periodicals; Geophysics -- Periodicals; 551.5
• DOI: 10.1029/2022JD038046
• Languages: English
• ISSNs: 2169-897X

Abstract

Abstract: Evapotranspiration (ET) constitutes the water exchange from land to the atmosphere, which in turn modulates precipitation and soil moisture (SM). Multiple lines of evidence document complex feedbacks between changes in ET and temperature, atmospheric CO2 and vegetation greening. However, the existing analyses on global changes in ET do not account for the direct effects of SM supply and atmospheric water demand, expressed by vapor pressure deficit (VPD), while considering multiple environmental variables. Here we evaluated the performance of ET products using 140 flux towers included in the FLUXNET database. All ET products show reasonable performance, with an overall correlation higher than 0.7 and better performance at a higher latitude. From analysis of the ensemble mean of annual ET, we show insignificant ( P = 0.06) trends in global ET during 1982–2020 and a significantly ( P < 0.01) increasing trend during 2002–2020. Changes in GLEAM ET generally exert a positive response to changes in SM and a negative response to changes in VPD. Yet, these effects are not globally consistent and are largely determined by changes in vegetation transpiration. Using our finding as a benchmark, Earth System Models mostly reproduce the positive response of ET to SM with less coupling strength, while showing negative effects of VPD on ET with stronger coupling strength. Our study highlights that concurrent soil drying and atmospheric aridity could intensify water exchanges and the importance of realistically representing SM‐VPD‐ET interactions in models for accurate predictions of the hydrological cycle. Plain Language Summary: Evapotranspiration (ET) links the water exchange between land and the atmosphere, and thereby plays an important role in regulating precipitation and soil moisture (SM). In this study, using FLUXNET in situ observations we demonstrate the high performance of different ET products (GLEAM, ERA5, GLDAS, and MERRA2) which are widely used to characterize long‐term changes in global ET. Decreases in SM and increases in vapor pressure deficit (VPD) are expected to lead to decreases in ET worldwide. Using our observations as a benchmark, most of Earth System Models participating in the Coupled Model Intercomparison Project Phase 6 underestimate the positive response of ET to SM, while overestimating the negative effects of VPD on ET. This study provides a comprehensive understanding of the impacts of SM and VPD on global changes in ET. Key Points: Insignificant trends in global evapotranspiration (ET) over the last four decades, but significantly increasing trends in ET during recent two decades ET generally exerts a positive response to soil moisture (SM) and a negative response to vapor pressure deficit (VPD), but effects are not globally consistent Earth system models underestimate the response of ET to SM while overestimating the response of ET to VPD