Variations in Land-Atmosphere Coupling during Drought-Heatwave events

Droughts and heatwaves are linked through different land-atmosphere coupling pathways. While high temperatures and depleted soil moisture (SM) reserves are characteristic of all extreme compound drought-heatwave events, the behavior of latent heat flux (LHF) can reveal the dominant forcing mechanism driving these events. Our quantitative framework for grid-cell-by-grid-cell analysis shows that most cases across six severe compound drought-heatwave cases since 2000 exhibit spatially inhomogeneous land-atmosphere coupling, which are associated with the partitioning of surface fluxes. Atmospherically-driven regimes are characterized by increased LHF following daily maximum temperature anomalies, while regimes driven from the land surface show LHF deficits following SM anomalies. In addition, we demonstrate mechanistic skill with a medium-range forecast model in reproducing two events with contrasting coupling behaviors, with the more water-limited event exhibiting longer lead-time predictability. These results highlight the limitations of using domain-average coupling to characterize extremes, and the potential for improved forecast accuracy for compound drought-heatwave events.