Nonlinear increase of compound drought-heatwave events since the early 2000s

Compound drought-heatwave events (CDHEs) have substantially increased since the early 2000s, posing elevated risks to socio-ecosystems. However, the physical characteristics of drought- and heatwave-leading CDHEs and their relative contributions to the overall increase remain unexplored. Using a multihazard pair generation algorithm with daily reanalysis data, we show that both drought- and heatwave-leading CDHEs increased nonlinearly over the past two decades relative to earlier decades. This pattern is evident at the global scale but also shows considerable regional variation. Focusing on heatwave-leading CDHEs which are associated with stronger intensification of the subsequent hazard than drought-leading events, we find that the nonlinear amplification of land-atmosphere coupling since the late 1990s has not only induced the emergence of statistically significant positive sensitivities in previously unresponsive regions, but also markedly enhanced sensitivities in high-occurrence regions. These findings highlight the importance of considering the disproportionate regional risks associated with heatwave-leading CDHEs when adapting to climate change.