Unraveling the spatiotemporal dynamics of compound heatwaves and extreme sea levels in a changing climate

Abstract

Compound heatwave-extreme sea level (CHWESL) events are sequential extremes in which an extreme sea level closely follows a heatwave, affecting water availability, human societies, and ecosystems. However, current research lacks comprehensive spatiotemporal analyses examining the interplay between heatwaves and extreme sea levels, particularly in the context of climate change. In this study, we utilize ERA5 reanalysis data, GESLA observational data, and EURO-CORDEX climate model simulations to investigate the frequency, dependence, and potential indicators of these compound events. Our findings indicate that the average probability of CHWESL occurrences is 22.6 %. We confirm that two-thirds of CHWESL events result from the dependence between heatwaves and extreme sea levels, as demonstrated by a resampling-based significance test. Nearly half of the coastal areas have experienced an increase in the frequency of CHWESL events in recent years, with an average rate of 0.4 events per decade. Notably, CHWESL events exhibit an average air temperature that is 0.3 °C higher than heatwaves not followed by extreme sea levels, with the maximum difference reaching up to 4.7 °C. Additionally, low surface pressure during hotter heatwaves serves as a critical indicator for the occurrence of CHWESL events. By mid-century, under a high-emission scenario, the frequency of CHWESL events is projected to increase eightfold compared to that during the historical period, primarily due to the rising frequency of heatwaves. Overall, this study enhances our understanding of the current and future risks associated with CHWESL events and underscores the importance of adaptation measures to mitigate the adverse impacts of increasing compound events.