Escalating Ecological Droughts Driven by Compound Soil and Atmospheric Dryness.

Intensifying droughts are increasingly pushing ecosystems beyond functional thresholds, threatening carbon uptake, biodiversity, and ecosystem resilience. However, the dominant drivers and spatiotemporal patterns of ecological droughts remain poorly understood. Here, we develop an impact-based optimality framework to identify ecological droughts, quantify their impacts on ecosystem photosynthesis, and assess the relative roles of soil and atmospheric dryness using an ensemble of global observation-constrained datasets. We find that 52% of land areas experience ecological droughts driven by compound soil and atmospheric dryness, contributing 55% of global drought-induced carbon losses. In contrast, other regions are dominated by soil or atmospheric drought alone. Notably, compound drought regions account for the majority of global increases in ecological drought frequency (57%), intensity (64%), and carbon losses (63%) over the past four decades. Our findings highlight the growing importance of compound ecological droughts in shaping ecosystem vulnerability, threatening the stability of terrestrial carbon sinks, and potentially amplifying carbon-climate feedbacks.