Hao et al. (2025) Evaluating ecosystem water use efficiency and recovery dynamics during flash droughts: insights from observations and model simulations

Identification

• Journal: Agricultural and Forest Meteorology
• Year: 2025
• Date: 2025-12-13
• Authors: Yuefeng Hao, Jiafu Mao, Yaoping Wang, Lianhong Gu, Jeffrey Wood, Paul J. Hanson, Melanie A. Mayes, Mingzhou Jin, Peter E. Thornton, Xiaoying Shi, Daniel M. Ricciuto
• DOI: 10.1016/j.agrformet.2025.110982

Research Groups

• Institute for a Secure and Sustainable Environment, The University of Tennessee, Knoxville, TN, USA
• Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA
• School of Natural Resources, University of Missouri, Columbia, MO, USA

Short Summary

This study investigates ecosystem water use efficiency (WUE) and its components (gross primary production, GPP; actual evapotranspiration, AET) during flash droughts using observations and the ELMv2 model. It finds that ELMv2 captures shifting GPP/AET dynamics but systematically underestimates GPP, AET, and WUE, and prolongs GPP recovery, highlighting the need to integrate plant hydraulics for improved flash drought predictability.

Objective

• To investigate the dynamics of landscape-scale ecosystem water use efficiency (WUE), gross primary production (GPP), and actual evapotranspiration (AET) under flash drought (FD) conditions.
• To evaluate the performance of the U.S. Department of Energy’s Earth, Energy, Exascale System Model (E3SM) Land Model (ELMv2) in simulating these dynamics compared to observed data.

Study Configuration

• Spatial Scale: Local scale (Missouri Ozark AmeriFlux site, US-MOz).
• Temporal Scale: Multi-year analysis of specific flash drought events (2005, 2007, 2012, 2014, 2018).

Methodology and Data

• Models used: E3SM Land Model version 2 (ELMv2).
• Data sources: Observed data from the Missouri Ozark AmeriFlux site (US-MOz), including measurements of GPP, AET, vapor pressure deficit (VPD), soil moisture (SM), and predawn leaf water potential (PLWP).

Main Results

• GPP was the dominant regulator of WUE during earlier flash drought events (2005, 2007, 2012), while AET became dominant in more recent events (2014, 2018).
• ELMv2 systematically underestimated both GPP and AET, and consequently WUE, suggesting a stronger underestimation of GPP relative to AET.
• ELMv2 underestimated the speed of GPP recovery following flash drought events, leading to artificially prolonged recovery times.
• Observed environmental drivers (VPD, SM, PLWP) effectively predicted WUE, but ELMv2 primarily emphasized the role of soil moisture, underestimating the influence of VPD.
• Relying solely on soil moisture in models fails to capture the rapid hydraulic recovery observed in predawn leaf water potential.

Contributions

• Provides novel insights into the shifting dynamics of GPP and AET in regulating ecosystem WUE during flash droughts using both observations and a state-of-the-art land surface model (ELMv2).
• Identifies specific biases in ELMv2's simulation of GPP, AET, WUE, and GPP recovery speed during flash droughts.
• Highlights the critical importance of integrating plant hydraulics into land surface models to improve the predictability of flash droughts and their impacts on ecosystem carbon-water cycling, particularly regarding the role of VPD and rapid hydraulic recovery.

Funding

• UT-Battelle, LLC, under contract no. DE-AC05-00OR22725 with the US Department of Energy (DOE).

Citation

@article{Hao2025Evaluating,
  author = {Hao, Yuefeng and Mao, Jiafu and Wang, Yaoping and Gu, Lianhong and Wood, Jeffrey and Hanson, Paul J. and Mayes, Melanie A. and Jin, Mingzhou and Thornton, Peter E. and Shi, Xiaoying and Ricciuto, Daniel M.},
  title = {Evaluating ecosystem water use efficiency and recovery dynamics during flash droughts: insights from observations and model simulations},
  journal = {Agricultural and Forest Meteorology},
  year = {2025},
  doi = {10.1016/j.agrformet.2025.110982},
  url = {https://doi.org/10.1016/j.agrformet.2025.110982}
}