Growing Threats From Swings Between Hot and Wet Extremes in a Warmer World.

The abrupt alternation between hot and wet extremes can lead to more severe societal impacts than isolated extremes. However, despite an understanding of hot and wet extremes separately, their temporally compounding characteristics are not well examined yet. Our study presents a comprehensive assessment of successive heat‐pluvial and pluvial‐heat events globally. We find that these successive extremes within a week occur every 6–7 years on average within warm seasons during 1956–2015, about 15% more often than would be expected by chance, and that they have a significant increase in frequency of about 22% per decade due to warming. We further investigate the role of vapor pressure deficit (VPD) and find that heat‐pluvial (pluvial‐heat) events are linked to negative (positive) VPD anomalies. Our results are statistically significant based on moving‐blocks bootstrap resampling and field significance tests, highlighting these methods' importance in robustly identifying compound events under autocorrelation and multiple‐testing conditions. Plain Language Summary: In recent years, the world has experienced various clustered weather and climate extremes, which are highly disruptive to humans and society. However, current knowledge on the risk of successive occurrence of hot (humid heat, including the effects of both temperature and humidity) and wet (pluvial flooding, usually caused by extreme rainfall) extremes remains unclear. In this study, we present a comprehensive assessment of the two types of interacting hot and wet extremes: humid heat extremes followed by pluvial flooding (heat‐pluvial) and extreme pluvials followed by humid heat (pluvial‐heat). We find that these events have increased significantly in most regions of the world for the last three decades, which can be associated with the warming effect. Importantly, we identify that the vapor pressure deficit plays an important but varying role in the abrupt alternation between heat and pluvial events. We emphasize the importance of using reliable statistical tests to ensure the validity of the results for complex compound events. Our analysis highlights the need for policymakers and stakeholders to develop adaptation strategies to cope with overlapping vulnerabilities due to compound hot and wet extremes, especially in areas prone to both such as West Australia, South America and Sub‐Saharan Africa. Key Points: Temporally compounding heat and pluvial events occur about 15% more often than would be expected by chanceIncreases in hot‐wet compound events have largely been linked to warmingVapor‐pressure‐deficit anomalies are a signature of heat‐pluvial versus pluvial‐heat sequences, a conclusion drawn from field significance tests [ABSTRACT FROM AUTHOR]