Vegetation groundwater use drives streamflow declines in Colorado River headwaters

Vegetation groundwater use drives streamflow declines in Colorado River headwaters | 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 Vegetation groundwater use drives streamflow declines in Colorado River headwaters Harry Stone, Reed Maxwell This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8735125/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted You are reading this latest preprint version Abstract Snowmelt-driven regions provide water for billions of people, yet warming threatens to reduce streamflow from these watersheds1,2. The mechanics linking rising temperatures and streamflow decline remain poorly understood3, partly because snowfall takes months to become summer streamflow and steep terrain hinders direct observation. Here we show that vegetation in Colorado River headwaters draws on shallow stream-bound groundwater to sustain evapotranspiration during dry periods. Daily fluctuation patterns in soil moisture, groundwater, and streamflow indicate roots intercept groundwater to support transpiration when surface soils dry. Extending this analysis basin-wide across 18 headwater catchments, we demonstrate that summer temperature independently regulates streamflow with effects rivaling those of snowpack: warm summers reduce flows from high-snowpack years to average levels, while cool summers substantially elevate flows from moderate-snowpack years. These results reveal that growing-season temperature—not just winter precipitation—controls streamflow through groundwater-supported evapotranspiration. As warming continues and droughts intensify4, this unaccounted vegetation-groundwater pathway will deepen streamflow declines beyond those from reduced snowpack alone, with critical implications for water management in snowmelt-dependent regions. Earth and environmental sciences/Hydrology Earth and environmental sciences/Climate sciences/Climate change/Climate-change impacts Full Text Additional Declarations There is NO Competing Interest. Cite Share Download PDF Status: Under Review Version 1 posted 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. 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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-8735125","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":587198311,"identity":"ff7a2796-00fc-443f-84d6-f77f711c2179","order_by":0,"name":"Harry Stone","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA+ElEQVRIiWNgGAWjYBACAwST+QAyl5mQFhDFlgClidfCA2UT0mLOfvbZZ54/f+TM2Xu+Pa4ouCPPL9987AFDhXViAw4tlj3pxrN52wyMLXvObjc8Y/DMcGYbW7oBw5l0nFoMDqQxM/M2GCRuuJG7TbLB4HCCwTEeMwnGtsO4tZx/xszM8weo5f6bZ2At9mAt//BouQG0hYcNZAsPG8QWNpCWBnxanjEzzm0zNjY4k2ZuCNRiOONYWppEwrF0Y9wOS2NmePNHTs7g+OFnDxv+HJbnbz58TOJDjbUsLi0gwMQDodkQQgl4lIMA4w8MLaNgFIyCUTAKkAAAwolWALhk/6kAAAAASUVORK5CYII=","orcid":"https://orcid.org/0009-0002-2065-5605","institution":"Princeton University","correspondingAuthor":true,"prefix":"","firstName":"Harry","middleName":"","lastName":"Stone","suffix":""},{"id":587198312,"identity":"9593fa3d-a8d9-47f9-ae5e-dbc5c49fbe12","order_by":1,"name":"Reed Maxwell","email":"","orcid":"https://orcid.org/0000-0002-1364-4441","institution":"Princeton University","correspondingAuthor":false,"prefix":"","firstName":"Reed","middleName":"","lastName":"Maxwell","suffix":""}],"badges":[],"createdAt":"2026-01-29 20:55:50","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8735125/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8735125/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":102397438,"identity":"e87e5259-e979-4d3d-b439-fcbf8fbc5038","added_by":"auto","created_at":"2026-02-11 10:16:56","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1767802,"visible":true,"origin":"","legend":"Article File","description":"","filename":"Vegetationwateruse.Nature.stone.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8735125/v1_covered_d8eff33a-b27c-4dbb-a9a4-6e7a67157563.pdf"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Vegetation groundwater use drives streamflow declines in Colorado River headwaters","fulltext":[],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":false,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"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":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-8735125/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8735125/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"Snowmelt-driven regions provide water for billions of people, yet warming threatens to reduce streamflow from these watersheds1,2. 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