Local Land-Climate Dynamics Worsen Climate Extremes and Heighten the Risk of Heat Stress for Humans

Heatwave dynamics exhibit unique spatial heterogeneity, posing cascading environmental and societal challenges. Employing bias-adjusted climate models, we unveil these complexities by investigating heatwave dynamics, population exposure, and compound hydrometeorological extremes across 50 global regions within historical (1979-2014) and future epochs (2025-2060 and 2065-2100) under Shared Socio-economic Pathways (SSPs) 245 and 585. Our analysis reveals intricate couplings between heatwave occurrence and interlinked hydrometeorological extremes, including droughts and synergistic dry-hot events, regulated by large-scale atmospheric and terrestrial processes. Each region presents a unique climatological fingerprint, emphasizing the imperative for region-specific assessments over generalized approaches. For instance, robust lower-tropospheric moisture advection from the Atlantic Ocean into West and Central Africa, amplified by monsoonal winds, co-occurs with a Saharan monsoon trough and a weak Mediterranean ridge, mitigating heatwave frequency in these regions. Moreover, vertically integrated moisture flux convergence emerges as the dominant driver modulating heatwave frequency in the South American Monsoon zone, accounting for 41% of its variability. Relative humidity at 700 hPa and zonal winds at 1000 hPa also play significant roles, contributing 32% and 27%, respectively. Future projections depict a quadrupling of both heatwave frequency and compound events, exacerbating thermal stress and amplifying regional vulnerability. Population exposure to heatwaves is projected to escalate, exceeding fourfold and tenfold in the near- and far-future, respectively. Notably, South America and Europe exhibit substantial climate-driven exposure across all scenarios, underlining the urgency of regionally tailored adaptation and mitigation strategies in a warming planet.