Bai et al. (2026) Widespread enhancement of ecosystem carbon fluxes during post moisture pulse

Identification

• Journal: Communications Earth & Environment
• Year: 2026
• Date: 2026-01-14
• Authors: Yu Bai, Fangyue Zhang, Philippe Ciais, Jean-Pierre Wigneron, Andrew F. Feldman, Pierre Gentine, William K. Smith, Joel A. Biederman, Russell L. Scott, Paul Stoy, Dan Yakir, Armen R. Kemanian, David Makowski, Chuixiang Yi, Zheng Fu
• DOI: 10.1038/s43247-026-03191-x

Research Groups

• Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, China
• College of Water Sciences, Beijing Normal University, China
• Laboratoire des Sciences du Climat et de l’Environnement (LSCE/IPSL), CEA-CNRS-UVSQ, Université Paris-Saclay, France
• ISPA, INRAE, Université de Bordeaux, Bordeaux Sciences Agro, France
• NASA Goddard Space Flight Center, Biospheric Sciences Laboratory, USA
• Earth System Science Interdisciplinary Center, University of Maryland, USA
• Department of Earth and Environmental Engineering, Columbia University, USA
• School of Natural Resources and the Environment, University of Arizona, USA
• USDA Agricultural Research Service Southwest Watershed Research Center, USA
• Department of Biological Systems Engineering, University of Wisconsin-Madison, USA
• Earth and Planetary Sciences, Weizmann Institute of Science, Israel
• Department of Plant Science, The Pennsylvania State University, USA
• Unit Applied Mathematics and Computer Science (UMR MIA-PS) INRAE AgroParisTech Université Paris-Saclay, France
• School of Earth and Environmental Sciences, Queens College, City University of New York, USA
• Earth and Environmental Sciences Department, Graduate Center, City University of New York, USA

Short Summary

This study quantifies global ecosystem carbon and water flux responses during post-moisture dry-down events using eddy-covariance observations, revealing a widespread, transient enhancement of net carbon uptake that Earth System Models significantly underestimate. It demonstrates that photosynthetic capacity and radiation drive initial positive responses, while water limitations lead to subsequent declines.

Objective

• To quantify the changes in ecosystem carbon and water fluxes during post-moisture pulses across terrestrial ecosystems.
• To examine ecosystem-specific responses to these moisture pulses.
• To identify the drivers controlling the spatial variability of Gross Primary Production (GPP) changes during dry-downs.
• To evaluate how Earth System Models (CMIP6) simulate GPP responses, highlighting their biases relative to observation-based maps.

Study Configuration

• Spatial Scale: Global, utilizing 215 eddy-covariance flux tower sites and gridded data at 0.5° spatial resolution.
• Temporal Scale: Daily, focusing on 6502 soil dry-down events lasting at least 10 consecutive days, covering periods from 2009 to 2018 for observational data and 2005 to 2014 for model simulations.

Methodology and Data

• Models used:
  • Random Forest (RF) models for identifying drivers of GPP changes.
  • Five Earth System Models (ESMs) from CMIP6: ACCESS-ESM1-5, CMCC-CM2-SR5, IPSL-CM6A-LR, NorESM2-LM, and NorESM2-MM.
• Data sources:
  • Eddy-covariance measurements from FLUXNET2015, AmeriFlux, and ICOS networks (215 sites).
  • Global daily FLUXCOM RS+METEO GPP (0.5° resolution).
  • Gridded daily surface soil moisture (0-7 cm) from ERA5-Land reanalysis (0.1° resolution, resampled to 0.5°).
  • Global daily solar-induced chlorophyll fluorescence (SIF) from the TCSIF dataset (GOME-2A SIF).
  • Climatic variables (precipitation, potential evapotranspiration, vapor pressure deficit, shortwave radiation, air temperature) and vegetation characteristics (maximum leaf area index, soil texture, aridity index).

Main Results

• During early dry-down days, Gross Primary Production (GPP) and ecosystem respiration (Re) both increased compared to control periods, with GPP gains exceeding Re, leading to enhanced net carbon uptake.
• The median ΔGPP (difference in GPP between dry-down and control) peaked at 0.6 grams of carbon per square meter per day (gC m−2 day−1) around the third day, then gradually diminished.
• Latent heat flux (ΔLE) was initially positive (median 24 watts per square meter (W m−2) during the first 10 days) but declined over time, while sensible heat flux (ΔH) consistently increased as soil moisture (SM) decreased.
• Machine-learning analysis showed that photosynthetic capacity (maximum leaf area index, LAImax) and radiation (ΔRAD) were the primary drivers of positive GPP anomalies, whereas water limitations (changes in SM, ΔSM, and vapor pressure deficit, ΔVPD) induced negative GPP anomalies.
• Positive ΔGPP persisted for approximately 9, 13.5, and 17 days during dry-downs lasting ≥10, 15, and 20 days, respectively, before transitioning to negative values.
• Earth System Models (ESMs) significantly underestimated the magnitude of ΔGPP, with underestimations of 67%, 83%, and 90% for dry-downs lasting ≥10, 15, and 20 days, respectively, compared to FLUXCOM GPP.
• A lower soil moisture threshold for photosynthetic limitation (θGPP) was identified compared to the critical soil moisture threshold for plant water stress (θcrit based on evaporative fraction), suggesting photosynthesis can tolerate drier conditions than overall plant water stress.

Contributions

• Provides the first global-scale quantification of ecosystem carbon and water flux changes during post-moisture pulse dry-down events, extending the "pulse-reserve" paradigm beyond drylands to diverse biomes.
• Utilizes a robust natural experiment design with global eddy-covariance observations and satellite data to isolate transient ecosystem responses to moisture pulses.
• Identifies key environmental and vegetation drivers of both positive and negative GPP responses using explainable machine learning (Random Forest with SHAP analysis).
• Reveals significant underestimation of observed GPP enhancement during dry-downs by CMIP6 Earth System Models, highlighting critical biases and the urgent need for improved model representation of water-stress responses and soil-atmosphere interactions.

Funding

• National Key R&D Program of China (2024YFF1309000)
• National Natural Science Foundation of China (42471122)
• Chinese Academy of Sciences (2024000275)
• NSFC Excellent Young Scientists Fund (Overseas)
• Postdoctoral Fellowship Program of CPSF (GZB20240733)
• China Postdoctoral Science Foundation

Citation

@article{Bai2026Widespread,
  author = {Bai, Yu and Zhang, Fangyue and Ciais, Philippe and Wigneron, Jean-Pierre and Feldman, Andrew F. and Gentine, Pierre and Smith, William K. and Biederman, Joel A. and Scott, Russell L. and Stoy, Paul and Yakir, Dan and Kemanian, Armen R. and Makowski, David and Yi, Chuixiang and Fu, Zheng},
  title = {Widespread enhancement of ecosystem carbon fluxes during post moisture pulse},
  journal = {Communications Earth & Environment},
  year = {2026},
  doi = {10.1038/s43247-026-03191-x},
  url = {https://doi.org/10.1038/s43247-026-03191-x}
}