Trans-Seasonal Vegetation-Land-Atmosphere Interactions Explained Record-Breaking Cascading Extremes in the Upper Reaches of the Yangtze River

The upper reaches of the Yangtze River observed record-breaking droughts, heatwaves, and forest fires in rapid sequence during the 2022 summer, challenging the established mechanistic understanding. We here explained the compound event through a trans-seasonal vegetation-land-atmosphere interacting perspective. The wetter spring and sunnier summer pattern resulted in record high loads of vegetation and enhanced transpiration. This led to progressive depletion of soil moisture to a critical threshold that shifted the originally weak response of air temperature into hypersensitive mode. The resulting rapid rise of air temperature amplified atmospheric evaporative demand to an unprecedentedly high level, which in turn exacerbated the drying-out of soil and vegetation. These favorable weather and fuel factors combined to cause unseasonal forest fires of unprecedented burning intensity. Our results remind of preparedness against drought-heat-fire compounding hazards even in humid regions under opportune configurations between ecological and meteorological conditions.