Future heat-stress regimes under CMIP6: a multi-index assessment of persistence and human-relevant thermal constraints

Future heat-stress regimes under CMIP6: a multi-index assessment of persistence and human-relevant thermal constraints | 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 Research Article Future heat-stress regimes under CMIP6: a multi-index assessment of persistence and human-relevant thermal constraints Tiffanie Lescure, Dimitri Defrance This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9022803/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 7 You are reading this latest preprint version Abstract Human exposure to heat stress is increasing under climate change as rising temperatures interact with atmospheric moisture to constrain thermoregulation and outdoor activity. While numerous heat-stress indices are used in climate impact studies, their joint interpretation in terms of climatic regimes, persistence, and physiological relevance remains fragmented. Here, we provide a global, multi-model assessment of future human-relevant heat stress using a consistent set of biometeorological indices derived from CMIP6 climate projections.We analyse daily bias-corrected projections from the NASA NEX-GDDP-CMIP6 dataset at 0.25 \((^\circ)\) resolution, using five CMIP6 models under SSP1--2.6, SSP2--4.5, and SSP5--8.5 scenarios. Wet-bulb temperature (Tw), wet-bulb globe temperature (WBGT), Heat Index, and Humidex are computed consistently and evaluated against ERA5 for the historical period. Heat stress is characterised through mean conditions, peak daily stress, and chronic threshold exceedance, defined as at least 30 days per year above physiologically and operationally relevant thresholds.All indices indicate a robust intensification of heat stress under future warming, reflecting a systematic elevation of baseline thermal environments rather than isolated extremes. Under SSP5--8.5, more than five billion people are projected to experience at least one month per year with WBGT \((\geq)\) 32 \((^\circ)\) C by late century, while over two billion may be exposed to chronic extreme humid heat (Tw \((\geq)\) 35 \((^\circ)\) C). These exposures are concentrated in densely populated tropical and subtropical regions, particularly in Asia and Africa, and are substantially reduced under lower-emission pathways.WBGT-based exceedance highlights expanding constraints on sustained outdoor activity, whereas extreme wet-bulb temperature represents a fundamental atmospheric limit to evaporative cooling. By distinguishing between mean intensification, peak stress, and persistence-based exceedance across multiple indices, this study provides a climatologically grounded framework for assessing emerging heat-stress regimes relevant to applied climatology, climate services, and long-term adaptation planning. Heat stress Biometeorology Wet-bulb globe temperature (WBGT) Wet-bulb temperature Climate projections Chronic heat exposure Full Text Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Reviews received at journal 02 Apr, 2026 Reviewers agreed at journal 26 Mar, 2026 Reviewers agreed at journal 25 Mar, 2026 Reviewers invited by journal 16 Mar, 2026 Editor assigned by journal 05 Mar, 2026 Submission checks completed at journal 05 Mar, 2026 First submitted to journal 03 Mar, 2026 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. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9022803","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":607666086,"identity":"be48fa10-cedd-46a9-a512-f28939bdfcc1","order_by":0,"name":"Tiffanie Lescure","email":"","orcid":"","institution":"CosmosClimae","correspondingAuthor":false,"prefix":"","firstName":"Tiffanie","middleName":"","lastName":"Lescure","suffix":""},{"id":607666087,"identity":"786825dc-2304-49b0-9db6-728990b73e36","order_by":1,"name":"Dimitri Defrance","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA4UlEQVRIiWNgGAWjYDCCwwwMBxgYJORgfBk2orQcYJAwhvF5CGs5AMGJDTAtBHXwHedOPPxxj0V6f3v70w0f/tjx8IkdfviAocYmGpcWycO8Gw4ceCaRO+PMGbObM9uSedik04wNGI6l5Tbg0GIA1nJAIneDRA7bbd6GA0AtCWYSjA2HCWpJN5BIf3ab5w9IS/r3H8RoSTCQSDC7zcMG0pJjxoBPC9gvZw5IGCL5JadYIgGPX/jOn938oeJAnTx/e/uzG8AQk5Ofnb7xw4caG5xacIAE0pSPglEwCkbBKEADAFrrX2mvdJYTAAAAAElFTkSuQmCC","orcid":"","institution":"CosmosClimae","correspondingAuthor":true,"prefix":"","firstName":"Dimitri","middleName":"","lastName":"Defrance","suffix":""}],"badges":[],"createdAt":"2026-03-03 17:53:15","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9022803/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9022803/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":105034586,"identity":"8a7adc11-4a76-41e5-99e8-b306f24fd49f","added_by":"auto","created_at":"2026-03-20 07:23:40","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":5834514,"visible":true,"origin":"","legend":"","description":"","filename":"ChangementClimatettravail.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9022803/v1_covered_9c6ed393-683b-4e1e-ba3b-45e983a6aeda.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Future heat-stress regimes under CMIP6: a multi-index assessment of persistence and human-relevant thermal constraints","fulltext":[],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":false,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":true,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":true,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"theoretical-and-applied-climatology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"taac","sideBox":"Learn more about [Theoretical and Applied Climatology](https://www.springer.com/journal/704)","snPcode":"704","submissionUrl":"https://submission.nature.com/new-submission/704/3","title":"Theoretical and Applied Climatology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Heat stress, Biometeorology, Wet-bulb globe temperature (WBGT), Wet-bulb temperature, Climate projections, Chronic heat exposure","lastPublishedDoi":"10.21203/rs.3.rs-9022803/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9022803/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eHuman exposure to heat stress is increasing under climate change as rising temperatures interact with atmospheric moisture to constrain thermoregulation and outdoor activity. While numerous heat-stress indices are used in climate impact studies, their joint interpretation in terms of climatic regimes, persistence, and physiological relevance remains fragmented. Here, we provide a global, multi-model assessment of future human-relevant heat stress using a consistent set of biometeorological indices derived from CMIP6 climate projections.We analyse daily bias-corrected projections from the NASA NEX-GDDP-CMIP6 dataset at 0.25\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\((^\\circ)\\)\u003c/span\u003e\u003c/span\u003e resolution, using five CMIP6 models under SSP1--2.6, SSP2--4.5, and SSP5--8.5 scenarios. Wet-bulb temperature (Tw), wet-bulb globe temperature (WBGT), Heat Index, and Humidex are computed consistently and evaluated against ERA5 for the historical period. Heat stress is characterised through mean conditions, peak daily stress, and chronic threshold exceedance, defined as at least 30 days per year above physiologically and operationally relevant thresholds.All indices indicate a robust intensification of heat stress under future warming, reflecting a systematic elevation of baseline thermal environments rather than isolated extremes. Under SSP5--8.5, more than five billion people are projected to experience at least one month per year with WBGT \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\((\\geq)\\)\u003c/span\u003e\u003c/span\u003e 32\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\((^\\circ)\\)\u003c/span\u003e\u003c/span\u003eC by late century, while over two billion may be exposed to chronic extreme humid heat (Tw \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\((\\geq)\\)\u003c/span\u003e\u003c/span\u003e 35\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\((^\\circ)\\)\u003c/span\u003e\u003c/span\u003eC). These exposures are concentrated in densely populated tropical and subtropical regions, particularly in Asia and Africa, and are substantially reduced under lower-emission pathways.WBGT-based exceedance highlights expanding constraints on sustained outdoor activity, whereas extreme wet-bulb temperature represents a fundamental atmospheric limit to evaporative cooling. By distinguishing between mean intensification, peak stress, and persistence-based exceedance across multiple indices, this study provides a climatologically grounded framework for assessing emerging heat-stress regimes relevant to applied climatology, climate services, and long-term adaptation planning.\u003c/p\u003e","manuscriptTitle":"Future heat-stress regimes under CMIP6: a multi-index assessment of persistence and human-relevant thermal constraints","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-03-18 11:15:02","doi":"10.21203/rs.3.rs-9022803/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"editorInvitedReview","content":"","date":"2026-04-02T14:38:01+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"256534831557723065892437883832484639374","date":"2026-03-26T09:11:33+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"39523214543935816760428654606590114855","date":"2026-03-25T16:01:12+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-03-16T08:17:00+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-03-05T23:04:05+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-03-05T23:03:35+00:00","index":"","fulltext":""},{"type":"submitted","content":"Theoretical and Applied Climatology","date":"2026-03-03T17:47:50+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"theoretical-and-applied-climatology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"taac","sideBox":"Learn more about [Theoretical and Applied Climatology](https://www.springer.com/journal/704)","snPcode":"704","submissionUrl":"https://submission.nature.com/new-submission/704/3","title":"Theoretical and Applied Climatology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"88cf119e-4bf4-42ac-8478-41e259520237","owner":[],"postedDate":"March 18th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-03-18T11:15:02+00:00","versionOfRecord":[],"versionCreatedAt":"2026-03-18 11:15:02","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9022803","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9022803","identity":"rs-9022803","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}