Satellite-informed Reanalysis Reveals Decreasing Soil Moisture Driving Faster Formation and Dissipation of Soil Heatwaves

Soil temperature (ST) is a key state variable in land-atmosphere interactions, yet the dynamics, drivers and ecological associations of soil heatwaves (SHWs) remain poorly understood. Here, we used daily maximum ST from ECMWF Reanalysis v5 dataset (ERA5), the Global Land Data Assimilation System (GLDAS) and the Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2) to investigate global SHWs from 1980 to 2022 and Coupled Model Intercomparison Project Phase 6 (CMIP6) simulations to assess future changes from 2023 to 2100. SHWs were defined as events lasting at least five consecutive days during which daily maximum ST exceeded the calendar-day 90th percentile threshold at each grid cell. Correlation analysis, convergent cross mapping (CCM) and structural equation modelling (SEM) were used to examine hydrothermal pathways linking soil moisture (SM), surface energy fluxes and soil heatwave (SHW) dynamics, while the normalized difference vegetation index (NDVI) was used to assess vegetation-greenness associations. During 1980–2022, onset and decline rates increased across 61% and 81% of land grid cells, respectively, with spatial mean grid-cell trends of 1.5 × 10⁻² and 6.3 × 10⁻² °C/(d \cdot decade). Within the SEM framework, SM showed strong and consistent negative associations with onset and decline rates, with path coefficients of –0.7 and –0.89, respectively. SHW dynamics were also associated with vegetation greenness, with onset-rate relationships varying among climate regions and decline rate showing a positive global association with NDVI. Future projections indicated increasing SHW intensity and duration, whereas onset and decline rates showed nonlinear changes, with a short initial increase followed by a marked decrease toward approximately mid-century and weaker changes thereafter. These findings highlight the role of SM in SHW dynamics and the need to consider both the severity and temporal evolution of soil thermal extremes under climate warming.