Stronger impacts of spatial extent than duration on tree growth during megadroughts

Megadroughts are extreme drought events defined by exceptional severity, duration, and spatial extent, potentially causing irreversible impacts on regional hydrological conditions and terrestrial ecosystems. With climate change driving more frequent global droughts, the likelihood of megadroughts has increased. Yet, their spatiotemporal patterns, evolutionary trends, and ecological impacts over the past century remain underexplored. By using a state-of-the-art clustering method, we identified 50 megadrought events between 1901 to 2020, with geographical hotspots concentrated in the western United States, southern Africa, and the Mediterranean region. Both drought duration and spatial coverage have increased markedly alongside global warming. Analysis of tree-ring chronologies from 4,595 sites worldwide using mixed-effects models reveals that the spatial extent of droughts exhibit stronger negative impact on radial growth than drought duration. Extensive droughts are likely associated with enhanced atmospheric aridity and increased risks of insect outbreaks facilitated by regional-scale migration, thereby amplifying growth reductions. Our findings challenge the long-standing emphasis on drought duration as the primary determinant of ecosystem functioning.