Atmospheric drought dominates changes in global water use efficiency

Jingjing Yang; Xiaoliang Lu; Zhunqiao Liu; Xianhui Tang; Qiang Yu; Yunfei Wang

doi:10.1016/j.scitotenv.2024.173084

Atmospheric drought dominates changes in global water use efficiency

Sci Total Environ. 2024 May 10:934:173084. doi: 10.1016/j.scitotenv.2024.173084. Online ahead of print.

Authors

Jingjing Yang¹, Xiaoliang Lu², Zhunqiao Liu², Xianhui Tang¹, Qiang Yu³, Yunfei Wang⁴

Affiliations

¹ The Research Center of Soil and Water Conservation and Ecological Environment, Chinese Academy of Sciences and Ministry of Education, Yangling, Shaanxi 712100, China; Institute of Soil and Water Conservation, Chinese Academy of Sciences and Ministry of Water Resources, Yangling, Shaanxi 712100, China; University of Chinese Academy of Sciences, Beijing 100049, China.
² State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Northwest A&F University, Yangling, Shaanxi 712100, China.
³ State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Northwest A&F University, Yangling, Shaanxi 712100, China. Electronic address: yuq@nwafu.edu.cn.
⁴ School of Water Conservancy and Transportation, Zhengzhou University, Zhengzhou, Henan 450001, China. Electronic address: yunfei_wang@zzu.edu.cn.

PMID: 38735314
DOI: 10.1016/j.scitotenv.2024.173084

Abstract

Water use efficiency (defined as the ratio of gross primary productivity to plant transpiration, WUE_T) describes the tradeoff between ecosystem carbon uptake and water loss. However, a comprehensive understanding of the impact of soil and atmospheric moisture deficits on WUE_T across large regions remains incomplete. Solar-induced chlorophyll fluorescence (SIF) serves as an effective signal for measuring both terrestrial vegetation photosynthesis and transpiration, thereby enabling a rapid response to changes in the physiological status of plants under water stress. The objectives of this study were to: 1) mechanistically calculate WUE_T using top-of-canopy SIF data and meteorological information by using the revised mechanistic light response model and the Penman-Monteith equation; 2) analyze the effects of atmospheric and soil water deficits on SIF-based WUE_T by using decoupled soil water content (SWC) and vapor pressure deficit (VPD); 3) evaluate estimated SIF-based WUE_T against data from 28 eddy covariance (EC) flux sites representing eight different vegetation types. Results indicated that the model performed well in ecosystems with dense canopies, explaining 56 % of the daily variability in EC tower-based WUE_T. For the years 2019-2020, the global average WUE_T derived from SIF was 3.49 g C/kg H₂O. Notably, this value exceeded 4 g C/kg H₂O in tropical rainforest regions near the equator and went beyond 5 g C/kg H₂O in the high-latitude regions of the Northern Hemisphere. We found that SIF-based WUE_T was primarily influenced by VPD rather than SWC in over 90 % of the global vegetated area. The model used in this study increased our ability to mechanistically estimate WUE_T with SIF at the global scale, thereby highlighting the significance of the global response of SIF-based WUE_T to water stress, and also enhancing our understanding of the water‑carbon cycle in terrestrial ecosystems.

Keywords: Revised mechanistic light response model; Soil water content; Solar-induced fluorescence; Vapor pressure deficit; Water use efficiency.