Increasing trends of land and coastal heatwaves under global warming

Coastal heatwaves, which often coincide with typhoons, extreme sea levels, and other compound extreme events under global warming, are more complex and less studied compared to inland and marine heatwaves. In this study, a three-dimensional connected algorithm was used to detect spatiotemporal heatwave events during the summer seasons from 1959 to 2023 on a global scale. A novel method was developed to distinguish between land and coastal heatwaves by considering the movement of heatwaves during their lifecycle. Both land and coastal heatwaves increase in frequency and projection area but decrease in maximum intensity, with coastal heatwaves exhibiting a higher growth rate than land heatwaves. Across the Northern Hemisphere, metrics for both heatwave types demonstrate consistent upward trends. However, the Southern Hemisphere presents divergent patterns, with land heatwaves exhibiting a decreasing trend while coastal heatwaves continue to intensify. To assess the impacts of heatwave on human health, the heat stress index was analyzed during heatwave periods. The results indicate that heat stress conditions, currently classified under caution categories, are likely to escalate into more dangerous levels under global warming. This study provides critical insights into the different responses of land and coastal heatwaves to global warming and underscores the urgency of formulating effective disaster prevention strategies to mitigate their societal and environmental impacts.