Yoon et al. (2026) Variations in land-atmosphere coupling during drought-heatwave events

Identification

• Journal: Communications Earth & Environment
• Year: 2026
• Date: 2026-01-05
• Authors: Donghyuck Yoon, Jan-Huey Chen, Hsin Hsu, Kirsten L. Findell
• DOI: 10.1038/s43247-025-02977-9

Research Groups

• Program in Atmospheric and Oceanic Sciences, Princeton University, Princeton, NJ, USA
• Geophysical Fluid Dynamics Laboratory, National Oceanic and Atmospheric Administration (NOAA), Princeton, NJ, USA
• International Degree Program in Climate Change and Sustainable Development (IPCS), National Taiwan University, Taipei, Taiwan

Short Summary

This study quantitatively separates upward and downward land-atmosphere coupling mechanisms during six major drought-heatwave events, revealing spatially inhomogeneous coupling regimes that significantly influence medium-range forecast skill. It demonstrates that water-limited conditions, characterized by land surface-driven coupling, offer improved predictability compared to atmospherically-driven, energy-limited conditions.

Objective

• To advance the understanding of how variability in land-atmosphere coupling regimes shapes the overall characteristics of compound drought-heatwave events.
• To investigate how land-atmosphere regime-dependent behaviors influence the forecast skill of compound drought-heatwave events using a state-of-the-art forecast model.

Study Configuration

• Spatial Scale: Grid-based analysis covering the Northern Hemisphere, focusing on six historically impactful compound drought-heatwave events (2003 Western Europe, 2010 Eastern Europe and Russia, 2012 contiguous United States, 2021 Pacific Northwest, 2022 East Asia, 2023 Central America). Analysis performed at resolutions ranging from approximately 9 km to 0.1° for observational data and 13 km for model forecasts.
• Temporal Scale: Analysis of events since 2000, with a focus on 31-day lead-lag windows around heatwave peaks. Climatological baselines of 1991–2020 or 2000–2020. Medium-range forecasts extend up to 10 days.

Methodology and Data

• Models used:
  • GFDL SHiELD (System for High-resolution prediction on Earth-to-Local Domains)
  • Noah Land Surface Model (Noah-LSM)
  • Hydrology-Tiled ECMWF Scheme for Surface Exchanges over Land (H-TESSEL)
• Data sources:
  • Satellite/Observation: GLEAM (Global Land Evaporation and Soil Moisture), Integrated Multi-satellitE Retrievals for GPM (IMERG) Final Run precipitation data.
  • Reanalysis: ERA5-Land Daily Statistics (daily maximum surface air temperature (TMAX), surface soil moisture (SM), latent heat flux (LHF), sensible heat flux (SHF)), ERA5 (500-hPa geopotential height (GPH)).
  • Land Surface Analysis: GLDAS (Global Land Data Assimilation System).
  • Model Initialization: National Centers for Environmental Prediction (NCEP) Global Forecast System (GFS) analysis data.

Main Results

• Land-atmosphere coupling during drought-heatwave events is spatially inhomogeneous, associated with surface flux partitioning into distinct regimes.
• Atmospherically driven regimes, characterized by increased LHF following hot temperature anomalies (TMAX-LHF coupling), accounted for the majority (64.8%) of the 2022 East Asia event.
• Land surface-driven regimes, exhibiting LHF deficits following dry SM anomalies (SM-LHF coupling), were most prevalent (45.4%) in the 2023 Central America event.
• A medium-range forecast model (GFDL SHiELD) successfully reproduced these distinct coupling behaviors.
• The water-limited (2023 Central America) case exhibited a lead-time predictability improvement of approximately 2-3 days relative to the energy-limited (2022 East Asia) case.
• Evaporative fraction (EF) was significantly higher in TMAX-LHF coupling regimes (e.g., Regime I, mean EFp = 78-89%) compared to SM-LHF coupling regimes (e.g., Regime VII, mean EFp = 22-38%).
• In TMAX-LHF coupling regimes, EF was largely independent of SM, while in SM-LHF coupling regimes, EF was highly sensitive to SM, indicating a transition from energy-limited to water-limited conditions.

Contributions

• Provides a novel, grid-based quantitative separation of upward and downward land-atmosphere coupling mechanisms within compound drought-heatwave events, moving beyond domain-averaged analyses.
• Demonstrates that the spatial heterogeneity of land-atmosphere coupling regimes, linked to surface energy flux partitioning, is a critical factor in shaping the overall characteristics of these events.
• Establishes a direct link between specific land-atmosphere coupling regimes and the predictability of compound drought-heatwave events, showing improved forecast skill (2-3 days lead-time) in water-limited conditions.
• Highlights the potential for improving medium-range drought-heatwave forecasts by incorporating regime-based characteristics into numerical models.
• Suggests that temporal transitions between coupling behaviors can occur within subseasonal timescales (e.g., 31-day windows) during event evolution, which is crucial for understanding flash droughts.

Funding

• National Oceanic and Atmospheric Administration (NOAA), U.S. Department of Commerce (Award NA18OAR4320123 and NA23OAR4320198)
• NOAA Research Global-Nest Initiative

Citation

@article{Yoon2026Variations,
  author = {Yoon, Donghyuck and Chen, Jan-Huey and Hsu, Hsin and Findell, Kirsten L.},
  title = {Variations in land-atmosphere coupling during drought-heatwave events},
  journal = {Communications Earth & Environment},
  year = {2026},
  doi = {10.1038/s43247-025-02977-9},
  url = {https://doi.org/10.1038/s43247-025-02977-9}
}