Contrary effects of soil moisture-atmosphere feedback on dry and humid heatwaves.

Although soil moisture-atmosphere feedback (SAF) has been widely recognized as a key driver of temperature extremes, its distinct impacts on dry and humid heatwaves remain insufficiently understood, largely due to previous studies focusing predominantly on dry heatwaves alone. In this study, we combine SAF perturbation experiments from CMIP6 with partial differential analysis to construct a global map of SAF's influence on both humid and dry heatwaves during 1985-2014 and to elucidate the underlying mechanisms. Unlike the homogeneously amplifying effect of SAF on dry heatwaves, SAF reduces the duration and severity of humid heatwaves by 20-40% in low-to-mid latitude regions with strong soil moisture-atmosphere coupling. In contrast, it increases their duration and severity by ≥50% in high latitude regions. These spatially divergent responses are primarily attributed to the competition between SAF-induced thermal warming and moisture depletion, which respectively raise or lower wet-bulb temperatures. Our findings reveal a dual regulatory mechanism by which SAF influences heat extremes through temperature-humidity coupling, providing scientific insights for region-specific adaptation strategies to both dry and humid heatwaves.