Thermal Amplification of Drought and Hydroclimatic Regime Shift in the Pantanal Wetland

Abstract

The Pantanal, the world’s largest tropical wetland, is experiencing increasing hydroclimatic stress under sustained warming. Drought duration, severity, and intensity increased significantly after the early 2000s, resulting in the most persistent multi-year drought within the study period. This study assesses whether drought dynamics are becoming increasingly thermally amplified. The assessment integrates data and methods, including reanalysis data from 1980–2022, SPEI-12, Run Theory, climate-extreme indices, Random Forest analysis, land-cover and surface-water changes, and CMIP6 projections. Although declining precipitation remained important, warm-day frequency (TX90p) showed the strongest bivariate relationship with SPEI-12 across all Pantanal sectors (R² = 0.68–0.71) and the greatest explanatory importance among the evaluated extremes. This association is consistent with increasing thermal amplification, although TX90p and Thornthwaite-based SPEI-12 share sensitivity to air temperature. CMIP6 projections indicate TX90p increases under all scenarios, while the TX90p–SPEI-12 relationship becomes more coherent under SSP245 and especially SSP585. Land-surface transformation, wetland contraction, and surface-water loss coincided with drought intensification and may have weakened hydrological buffering, although their individual contributions could not be separated from climatic forcing. Overall, the Pantanal is shifting from a rainfall-buffered wetland toward more water-limited, thermally amplified drought conditions. Monitoring and adaptation should integrate temperature extremes, precipitation, soil moisture, evapotranspiration, and surface-water persistence rather than rainfall anomalies alone.