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Nonlinear increase of compound drought-heatwave events since the early 2000s PDF science.org/doi/reader/10.… 06MAR2026 Yong-Jun Kim, Sang-Wook Yeh et al science.org/doi/10.1126/sc… Abstract 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 this increase is primarily driven by heatwave-leading CDHEs, with the slope of increase in affected land area having risen nearly eightfold, from 1.6 to 13.1% per degree Celsius since the early 2000s. This pattern is evident at the global scale but also shows considerable regional variation. 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. INTRODUCTION Compound drought-heatwave events (CDHEs), the co-occurrence of droughts and heatwaves, have increased considerably since the beginning of the 21st century (1–4). These events have been exacerbating socioeconomic damage in sectors such as agriculture, ecosystems, and public health (5–7). For instance, in 2010, compound events accompanied by wildfires in Russia resulted in ~55,000 deaths (8, 9). Similarly, multiple heatwaves and droughts prolonged the unprecedented and devastating “Black Summer” bushfires in southeastern and eastern Australia (EAU) from 2019 to 2020 (10). More recently, the Pacific Northwest heatwave in June 2021 caused extreme drying conditions, leading to a 31% reduction in spring wheat yields and significant declines in barley, canola, and fruit production in British Columbia and Alberta, Canada (11). Numerous studies have investigated the recent upward trends in CDHEs using observational data (7, 12–14) and found that increasing anthropogenic activities have contributed to more frequent and intense CDHEs, particularly in low-income countries (15, 16). CDHEs are often initiated by atmospheric circulation anomalies, such as persistent blocking highs, which create prolonged hot and dry conditions. These conditions can be further intensified through land-atmosphere coupling, where soil moisture deficits and enhanced surface heating reinforce each other (17–22). However, the dynamics leading to CDHEs differ depending on the sequence of events (19, 23). In heatwave-leading CDHEs, increased solar radiation enhances evapotranspiration, leading to favorable conditions for surface droughts (fig. S1A). In contrast, in drought-leading CDHEs, soil moisture depletion restricts the emission of latent heat flux from the land surface to the atmosphere (fig. S1, B and C). This leads to an increase in sensible heat flux, subsequently raising surface air temperatures and generating favorable conditions for heatwaves (fig. S1D). Fig. 1. Spatial pattern and temporal trend of CDHEs. science.org/doi/10.1126/sc… (A) Spatial map showing the total number of CDHE occurrences throughout the study period (1980 to 2023) over the land areas during the warm season from 60°S to 60°N, highlighting the high-occurrence regions. (B) Temporal trends of the global spatial extent of CDHEs (in percent). Red and yellow bars represent heatwave-leading and drought-leading CDHEs, respectively. The blue (red) dashed line indicates the estimated trend in the global spatial extent of CDHEs during the past (1980 to 2001) and recent (2002 to 2023) 22-year periods, based on simple linear regression. The corresponding blue and red values represent the regression slopes and their standard errors at the 99% confidence level. (C) Relative increase ratio of each CDHE type in the recent 22-year period compared with the past 22-year period. The increase ratio was calculated based on the average spatial extent during the past 22-year period, serving as a baseline for comparison with the recent period.