Distinct dynamical and thermodynamic pathways compound to amplify extreme atmospheric rivers

Distinct dynamical and thermodynamic pathways compound to amplify extreme atmospheric rivers | 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 Distinct dynamical and thermodynamic pathways compound to amplify extreme atmospheric rivers Tim Whittaker, Alejandro Di Luca This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9115963/v1 This work is licensed under a CC BY 4.0 License Status: Under Revision Version 1 posted 11 You are reading this latest preprint version Abstract Atmospheric rivers (ARs) making landfall over western North America are a primary driver of extreme precipitation and flood hazard, yet the upper bounds of their intensity remain poorly constrained by the short observational record. Here, we combine a differentiable global climate model (∼1.4◦ )with high-resolution dynamical downscaling (∼0.11◦ ) to construct physically plausible storylines of unprecedented AR events along the coast of British Columbia. By optimizing minimal perturbations to historical initial conditions, we generate events that maximize integrated vapor transport (IVT) at landfall and exceed the observational record under present-day climate conditions. Pseudo-global warming perturbations under SSP5-8.5 provide a second pathway to unprecedented intensity through end-of-century warming. The two approaches amplify AR intensity through distinct mechanisms: the optimization primarily modifies the wind field, while the pseudo-global warming signal primarily increases atmospheric moisture. These contributions act on largely independent components of the IVT budget, and when both are included simultaneously in numerical experiments, the combined effect is nearly additive, with differences generally below 15%. Yet, while relatively small, non-linear effects are always positive and the most extreme physically plausible ARs therefore arise from the compounding of both drivers. However, the two pathways differ in precipitation efficiency: the dynamical amplification largely preserves the conversion of moisture transport to precipitation, whereas the thermodynamic amplification reduces it by up to 30%. These findings demonstrate that bounding the upper tail of AR hazard requires accounting for both dynamical variability and thermodynamic change. Earth and environmental sciences/Climate sciences Earth and environmental sciences/Hydrology Atmospheric River Storylines Regional Climate Models Rare Event Algorithm Optimal Control Full Text Additional Declarations No competing interests reported. Supplementary Files extremeARSI.zip Cite Share Download PDF Status: Under Revision Version 1 posted Editorial decision: Revision requested 20 Apr, 2026 Reviews received at journal 13 Apr, 2026 Reviews received at journal 10 Apr, 2026 Reviews received at journal 10 Apr, 2026 Reviewers agreed at journal 30 Mar, 2026 Reviewers agreed at journal 27 Mar, 2026 Reviewers agreed at journal 27 Mar, 2026 Reviewers invited by journal 24 Mar, 2026 Editor assigned by journal 19 Mar, 2026 Submission checks completed at journal 19 Mar, 2026 First submitted to journal 13 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. 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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-9115963","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":612304762,"identity":"e6d07d7d-9a99-4f49-864b-3a1be5da577e","order_by":0,"name":"Tim Whittaker","email":"data:image/png;base64,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","orcid":"","institution":"University of Quebec in Montreal","correspondingAuthor":true,"prefix":"","firstName":"Tim","middleName":"","lastName":"Whittaker","suffix":""},{"id":612304763,"identity":"90548898-41d8-4c70-bd87-38aa880ff01c","order_by":1,"name":"Alejandro Di Luca","email":"","orcid":"","institution":"University of Quebec in Montreal","correspondingAuthor":false,"prefix":"","firstName":"Alejandro","middleName":"Di","lastName":"Luca","suffix":""}],"badges":[],"createdAt":"2026-03-13 14:53:26","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9115963/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9115963/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":105566171,"identity":"e41d1fd8-5f73-41c9-b7ae-410181d14594","added_by":"auto","created_at":"2026-03-27 12:55:32","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":6691847,"visible":true,"origin":"","legend":"","description":"","filename":"extremeARmain.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9115963/v1_covered_226954db-4e7c-440b-b7bf-24a4cee2ecdc.pdf"},{"id":105513202,"identity":"da05e3dd-c870-4aa5-b450-2d359a209f38","added_by":"auto","created_at":"2026-03-26 22:24:15","extension":"zip","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":3215365,"visible":true,"origin":"","legend":"","description":"","filename":"extremeARSI.zip","url":"https://assets-eu.researchsquare.com/files/rs-9115963/v1/9096cc9217a411d3b00e1e1b.zip"}],"financialInterests":"No competing interests reported.","formattedTitle":"Distinct dynamical and thermodynamic pathways compound to amplify extreme atmospheric rivers","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":"npj-climate-and-atmospheric-science","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"npjclimatsci","sideBox":"Learn more about [npj Climate and Atmospheric Science](http://www.nature.com/npjclimatsci/)","snPcode":"41612","submissionUrl":"https://submission.springernature.com/new-submission/41612/3","title":"npj Climate and Atmospheric Science","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"NPJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Atmospheric River, Storylines, Regional Climate Models, Rare Event Algorithm, Optimal Control","lastPublishedDoi":"10.21203/rs.3.rs-9115963/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9115963/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"Atmospheric rivers (ARs) making landfall over western North America are a primary driver of extreme precipitation and flood hazard, yet the upper bounds of their intensity remain poorly constrained by the short observational record. 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