Seasonality is Changing for Extreme Dry and Humid Heat Events

Credit: Richard Vanlerberghe, Unsplash Editors’ Highlights are summaries of recent papers by AGU’s journal editors. Source: AGU Advances Extreme heat events are an increasing threat to human health and ecosystem sustainability. While their rising frequency under global warming is well documented, much less is known about how their seasonality is changing, including whether extreme heat is occurring earlier or later in the year, potentially catching societies and ecosystems unprepared. Ivanovich et al. [2026] characterize global changes in the seasonality of extremely dry and humid heat events using data from the Modern-Era Retrospective Analysis for Research and Applications (MERRA-2) over the period 1980-2024. Changes in seasonality are assessed by comparing the distribution of extreme heat events during 1980-1989 with that of the most recent decade in the historical record. The results reveal substantial shifts in extreme heat seasonality over the past 45 years, with both dry and humid extreme heat seasons expanding across much of the globe. Importantly, these changes are often asymmetric. In regions such as western Europe and northeastern Russia, changes are dominated by an increase in pre-season extremes-analogous to springtime events in the midlatitudes. In contrast, much of the United States, eastern Europe, and eastern China have experienced stronger changes in late-season extremes. The study also highlights important regional departures from the broader global trend. Although previous research has shown that the average warm season is lengthening substantially across the midlatitudes, some regions, including eastern Russia, have experienced a contraction of the extreme heat season. These regional asymmetries suggest that local and regional climate processes can modify, and in some areas, even outweigh the broader influence of global warming. By revealing not only where extreme heat seasons are expanding, but also when within the year the greatest changes are occurring, these findings provide a new perspective on evolving heat risks and can help inform climate adaptation and risk-mitigation strategies. Citation: Ivanovich, C. C., Cook, B., & McDermid, S. (2026). Extreme dry and humid heat seasons are changing asymmetrically. AGU Advances, 7, e2026AV002516. https://doi.org/10.1029/2026AV002516 —Alberto Montanari, Editor-in-Chief, AGU Advances Text © 2026. The authors. CC BY-NC-ND 3.0Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.