Compound marine and terrestrial heatwave risks in coastal regions

Marine and terrestrial heatwave events can cause devasting impacts on ecosystems, species, climatic processes, and have the potential to cascade into greater socioeconomic damages and crises for humans. Terrestrial and marine heatwaves have been extensively researched separately, yet substantially fewer attempts have been made to investigate co-occurring extreme heat events over the land and ocean for coastal regions. The few studies investigating co-occurring marine and terrestrial heatwaves have been regionally focused analyses mainly exploring trends, mechanisms/drivers, or specific impacts. These studies have allowed for a strong foundation in the understanding of the hazard. However, the point in which natural hazards transform into devasting social disasters depends on the exposure and vulnerability of societies to such hazards.

Currently, there is a lack of risk assessments for compound ocean-land extremes. This research aims to tackle this gap, by investigating how the risk of compound marine and terrestrial/atmospheric heatwaves has evolved over the historical period taking into account dynamic hazards, exposure, and vulnerability. Using observation-based and reanalysis climate data, we first identify the co-occurrence of compound marine and terrestrial heatwaves for three key coastal regions (Iberian coastal region, Humboldt Coast, and California Coast). We chose to represent exposure and vulnerability with three components, one for each of the affected systems (human, land and marine). For example, exposure is represented by integrating population density, cropland fraction, and total fishery catch in each grid cell. Likewise, vulnerability is represented by integrating proxy indicators such as population age structure, irrigated and rainfed crop fraction, small and large total fishery catch fraction, and human development index. Specifically designing the exposure and vulnerability indices with components of all three affected systems, our risk assessment is uniquely tailored for coastal compound marine and terrestrial heatwaves. In doing so, we contribute to holistic climate research by integrating terrestrial, oceanic, and human elements to improve the relevance of scientific climate knowledge for decision makers to better manage future risks.

Funded by the European Union (WorldTrans, GA 101081661). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or European Climate, Infrastructure and Environment Executive Agency (CINEA). Neither the European Union nor the granting authority can be held responsible for them. This work is supported by FCT, I.P./MCTES through national funds (PIDDAC): LA/P/0068/2020 - https://doi.org/10.54499/LA/P/0068/2020 , UID/50019/2025,  https://doi.org/10.54499/UID/PRR/50019/2025, UID/PRR2/50019/2025