Zhou et al. (2025) Future exposure to moist heat extremes linked to soil dryness

Identification

• Journal: npj Climate and Atmospheric Science
• Year: 2025
• Date: 2025-11-18
• Authors: Jingwei Zhou, Dragan Milošević, Adriaan J. Teuling
• DOI: 10.1038/s41612-025-01252-0

Research Groups

• Hydrology and Environmental Hydraulics Group, Wageningen University & Research, Wageningen, Netherlands
• Meteorology and Air Quality Group, Wageningen University & Research, Wageningen, Netherlands

Short Summary

This study investigates the global impact of soil moisture on moist heat stress using CMIP6 models, revealing that soil moisture dynamics significantly amplify moist heat extremes and increase global population exposure to wet-hot conditions, particularly in mid-latitudes, with regional variations in coupling strength.

Objective

• To investigate the impacts of soil moisture on moist heat stress at a global scale using the Land Surface, Snow and Soil Moisture Model Intercomparison Project (LS3MIP) dataset within CMIP6.
• To examine the spatial and temporal variations of soil moisture-moist heat coupling and identify regions most susceptible to moist heat stress.
• To isolate the effects of interactive soil moisture on moist heat by comparing experiments with and without interactive soil moisture, highlighting its pronounced role in hot and humid regions.

Study Configuration

• Spatial Scale: Global, with a focus on seven climate reference regions: East, South, and Southeast Asia (ESEA), Australia (AU), Eastern United States (EUS), Central America (CAM), Arabian Peninsula (ARP), Mediterranean region and Northern Africa (MNAF), and Eastern South America (ESA). Data interpolated to a common grid of 2.5° longitude by 1.875° latitude.
• Temporal Scale: Historical period (1980–2014 for climatological soil moisture, 2000–2030 for current period) and future period (2040–2070). Daily data used for analysis.

Methodology and Data

• Models used: Coupled Model Intercomparison Project Phase 6 (CMIP6) models, specifically from LS3MIP and ScenarioMIP. Three climate models were primarily used: IPSL-CM6, MPI-ESM, and CMCC (though daily heat fluxes and soil moisture data from CMCC were not available for all analyses). Experiments included a fully-coupled control run (CTL) and a prescribed soil moisture run (pdLC).
• Data sources:
  • CMIP6 model simulations (daily near-surface air temperature, near-surface relative humidity, surface sensible heat flux, surface latent heat flux, and total soil moisture from historical, SSP585, and LFMIP-pdLC experiments).
  • ERA5-Land global reanalysis dataset (for validation of CMIP6 results, including near-surface air temperature, dewpoint temperature, and volumetric soil water).
  • Gridded global population data for 2000, 2010, 2020, 2030, 2040, 2050, 2060, and 2070 from SEDAC of NASA, consistent with Shared Socioeconomic Pathways (SSP585).
  • Moist heat quantified using the Discomfort Index (DI), calculated from near-surface air temperature and relative humidity, with wet-bulb temperature as an intermediate step.
  • Statistical significance assessed using the Anderson-Darling test (AD test) for comparisons and the Spearman rho test for correlations.

Main Results

• Moist heat is most severe in tropical and extra-tropical regions, but mid-latitude regions are projected to experience significant increases (>2.4 °C) in intensity, amplified by soil moisture.
• Soil moisture dynamics intensify moist heat across most land regions, showing strong negative correlations, particularly in eastern South America and Central America.
• Conversely, the Arabian Peninsula and northern Africa exhibit diverse moist heat responses to soil moisture variations, including relatively positive correlations in some areas.
• High moist heat generally coincides with a high Bowen ratio and low soil moisture (e.g., in Eastern South America, high moist heat >24 °C with Bowen ratio >1 and soil moisture <700 kg/m²).
• Exceptions exist where high moist heat occurs with a low Bowen ratio and low soil moisture (e.g., in the Arabian Peninsula, high moist heat >28 °C with Bowen ratio <3 and soil moisture <200 kg/m²).
• Low moist heat conditions are typically associated with high soil moisture and a low Bowen ratio (e.g., in Central America, low moist heat <26 °C with Bowen ratio <0.1 and soil moisture >600 kg/m²).
• Soil moisture changes are increasing global population exposure to wet-hot extremes in most regions.
• In East, South, and Southeast Asia (ESEA) and the Arabian Peninsula (ARP), current population exposure to average normal humid heatwaves (≥27 °C for ≥3 consecutive days) exceeds 40%, projected to reach up to 80% by 2060 in ARP and 50% by 2070 for extreme humid heatwaves in ESEA.
• In the Eastern United States (EUS) and Eastern South America (ESA), population exposure to average normal humid heatwaves longer than 6 days is projected to be over 50% by 2070.
• Soil moisture changes predominantly amplify population exposure to humid heatwaves in most domains, with notable exceptions in the Arabian Peninsula and Mediterranean region and Northern Africa where it can sometimes mitigate exposure.

Contributions

• This study is the first to use the LS3MIP simulation from the CMIP6 dataset to provide a global overview of the interactions between soil moisture and moist heat.
• It pioneers the adoption of dynamically identified local peak moist heat seasons at the grid-cell level, ensuring analysis is centered on periods of maximum physiological threat specific to each location, which is vital for accurate global risk assessment.
• The research offers novel insights into the critical role of soil moisture in modulating moist heat stress, highlighting the necessity for more accurate representations of land surface processes and feedbacks in climate models.
• The findings contribute to the development of effective strategies for managing and mitigating moist heat risks and protecting vulnerable populations.

Funding

• China Scholarship Council (J.Z.)
• World Climate Research Programme (WCRP)
• Earth System Grid Federation (ESGF)
• Socioeconomic Data and Applications Center (SEDAC) of National Aeronautics and Space Administration (NASA)
• Copernicus Climate Change Service

Citation

@article{Zhou2025Future,
  author = {Zhou, Jingwei and Milošević, Dragan and Teuling, Adriaan J.},
  title = {Future exposure to moist heat extremes linked to soil dryness},
  journal = {npj Climate and Atmospheric Science},
  year = {2025},
  doi = {10.1038/s41612-025-01252-0},
  url = {https://doi.org/10.1038/s41612-025-01252-0}
}