Mapping Synchronous Heat Waves in the Northern Hemisphere: Insights from Climate Network Analysis

Abstract The frequency and severity of summertime synchronous extreme heat waves across the Northern Hemisphere are increasing with global warming, threatening ecosystems, economies, and human health. Understanding the spatiotemporal characteristics of these heat waves is therefore crucial. This study employs the event synchronization climate network method to objectively identify hotspot regions of synchronous extreme heat waves and their dominant synchronization patterns. It further explores the associated large-scale atmospheric circulation patterns and soil moisture feedback processes. Results show that regions including most of Europe, the western Arabian Peninsula, East Asia, Southeast Asia, and the western and southern parts of North America, as well as Greenland, are susceptible to synchronous heat waves. Notably, Southeast Asia and western North America show strong synchronization with the Caspian Sea, while East Asia and southern North America primarily synchronize with northern–central Europe. Southeast Asia–Caspian Sea and East Asia–northern–central Europe synchronization patterns are linked to wave-like anomalies suggestive of northwest–southeastward-propagating Rossby waves, whereas western North America–Caspian Sea and southern North America–central Europe synchronization patterns correspond to zonal wave trains. These circulation patterns feature concurrent anticyclonic anomalies over synchronized heat wave regions, favoring warming through adiabatic subsidence and increased solar radiation. Moreover, concurrent local soil moisture drying increases the likelihood of their co-occurrences by positive land–atmosphere feedback, which likely acts to intensify and prolong heat waves. These findings systematically map synchronous heat wave hotspots and synchronization patterns across the Northern Hemisphere, highlighting novel cross-latitudinal connections and establishing a foundation for future work to disentangle dynamic and thermodynamic influences. Significance Statement As global temperatures rise, extreme heat waves are becoming more frequent and severe, especially in the Northern Hemisphere. This study reveals that heat waves are increasingly occurring simultaneously across distant regions, such as Europe, North America, and Asia. These synchronous heat waves pose serious risks to ecosystems, agriculture, economies, and human health. By using a novel climate network analysis, this study identifies regions most vulnerable to these synchronous heat wave events and the pathways through which they are linked. Understanding these patterns is crucial for predicting future heat waves, improving climate models, and helping societies to better prepare for the widespread impacts of extreme heat as the planet continues to warm.