Human-induced escalation of compound coastal marine–terrestrial heatwave associated with humid-heat stress on European coasts

Human-induced escalation of compound coastal marine–terrestrial heatwave associated with humid-heat stress on European coasts | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Human-induced escalation of compound coastal marine–terrestrial heatwave associated with humid-heat stress on European coasts Armineh Barkhordarian, Eline Brunet, Johanna Baehr This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7636199/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 12 Dec, 2025 Read the published version in Scientific Reports → Version 1 posted 10 You are reading this latest preprint version Abstract European coastal regions—home to dense populations, critical infrastructure, and climate-sensitive ecosystems—are increasingly vulnerable to the compounding effects of marine–terrestrial heatwaves, defined here as events in which a marine heatwave fully encompasses a terrestrial heatwave within paired coastal land and adjacent ocean grid cells. Using satellite-based sea surface temperatures and station observations, we show a non-linear and accelerating rise in exposure to compound heatwave days across European coastlines over the past two decades. Of the analyzed regions, the Mediterranean exhibits the steepest increase, reaching nearly 78 compound marine-terrestrial heatwave days by 2022. Attribution analysis indicates that greenhouse-gas forcing (GHG) accounts for ~95% of the risk of the 2022 event (5–95% CI: 93–100%), with the CESM1-LE model estimating its probability of occurrence under a no-GHG-forcing scenario as less than 5% (5–95% CI: 7%–0%). Notably, the increase in exposure time in response to GHG forcing is nonlinear: the rarer the event under a no-GHG-forcing scenario, the greater its frequency amplification under GHG forcing. Results further reveal that coastal marine heatwaves amplify terrestrial heatwave exposure by up to 3.5 times. During compound events, land-based wet-bulb temperatures exceed 25.5 °C and specific humidity surpasses 19 g/kg, marking a clear shift toward humid heatwave regimes in coastal regions. These findings highlight the amplifying effect of marine heatwaves on the persistence of coastal terrestrial heat extremes through enhanced moisture and heat coupling at the land–sea interface. This underscore the urgent need for the development of targeted, region-specific adaptation strategies across Europe’s most vulnerable coastal zones. Earth and environmental sciences/Climate sciences Earth and environmental sciences/Environmental sciences Earth and environmental sciences/Natural hazards Earth and environmental sciences/Ocean sciences Full Text Additional Declarations No competing interests reported. Supplementary Files SupplementaryBarkhordarian.pdf Cite Share Download PDF Status: Published Journal Publication published 12 Dec, 2025 Read the published version in Scientific Reports → Version 1 posted Editorial decision: Revision requested 13 Nov, 2025 Reviews received at journal 11 Nov, 2025 Reviews received at journal 09 Nov, 2025 Reviewers agreed at journal 22 Oct, 2025 Reviewers agreed at journal 21 Oct, 2025 Reviewers invited by journal 07 Oct, 2025 Editor invited by journal 22 Sep, 2025 Editor assigned by journal 19 Sep, 2025 Submission checks completed at journal 18 Sep, 2025 First submitted to journal 17 Sep, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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