Divergent regional responses of soil moisture-air temperature coupling under future climate scenarios

Climate models project that hotspot regions where soil moisture (SM) influences air temperature (T) will shift and strengthen, affecting droughts and heatwaves, yet the mechanisms driving these changes remain uncertain. Here, we use Coupled Model Intercomparison Project Phase 6 output and find divergent regional responses in SM-T coupling to different future emission scenarios during boreal summer. Under the low-end SSP1-2.6 scenario, SM-T coupling expands across all historical hotspots, while under the high-end SSP5-8.5 scenario, warming produces a latitudinal contrast, where SM-T coupling weakens and contracts at low-to-mid latitudes of the Northern Hemisphere but strengthens at higher latitudes. Coupling also strengthens in the humid tropics south of the equator, where disproportionate evaporation increases offset precipitation gains and depletes soil moisture. These shifts are driven by dynamic and thermodynamic changes modulating the atmospheric and land segments of SM-T coupling. Additionally, the influence of the poleward expansion of the Hadley cells, more pronounced under SSP5-8.5, further pushes SM control on surface energy partitioning northward. Together, these divergent responses reveal a nuanced, scenario-dependent future for SM-T coupling.