River Channel Change Can Affect Flood Hazard and Risk as Much as Climate

River Channel Change Can Affect Flood Hazard and Risk as Much as Climate | 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 River Channel Change Can Affect Flood Hazard and Risk as Much as Climate Laurence Hawker, Stephen Darby, Louise Slater, Daniel Parsons, and 17 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5312185/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 Over a billion people globally are already exposed to the risk of flooding, but by 2050 this number is expected to double due to human-induced climate change, population growth, and encroachment into at-risk areas. Global Flood Models (GFMs) are vital tools for producing flood hazard maps supporting impact estimates and policy interventions. These GFMs represent river channels by typically assuming that the bankfull flow-carrying capacity equates to a river flow with a specified return period (RP) that is spatially and temporally invariant. However, bankfull capacity is determined by channel size, shape and roughness and so varies in response to erosion and sedimentation. To quantify the extent to which channel variability biases GFM predictions here we employ a typical GFM, the Fathom model, to a 135,000 km2 region of the Mississippi floodplain in a sensitivity analysis that evaluates how inundated areas and associated population exposures respond when forced with empirically-derived bankfull capacities. Our results show that since the typical RPs (< 1 year) of these present-day bankfull flows differ from the 2-year value normally assumed in GFMs, substantial underestimates of flood extent (9 to 59%, depending on flood magnitude) and populations exposed (15 to 118%) result. We also show that, over multi-decadal timescales, changes in past channel morphology are, depending on emissions scenario, of equal or greater importance in driving changes in simulated flood hazard and risk than changes in future climate. The evolution of bankfull capacity through space and time is therefore a first order control on flood hazard and risk, meaning it is vital that river channel variability and change is represented accurately in GFMs. Earth and environmental sciences/Hydrology Earth and environmental sciences/Natural hazards Earth and environmental sciences/Climate sciences/Climate change/Climate-change impacts/Environmental health 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. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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Global Flood Models (GFMs) are vital tools for producing flood hazard maps supporting impact estimates and policy interventions. These GFMs represent river channels by typically assuming that the bankfull flow-carrying capacity equates to a river flow with a specified return period (RP) that is spatially and temporally invariant. However, bankfull capacity is determined by channel size, shape and roughness and so varies in response to erosion and sedimentation. To quantify the extent to which channel variability biases GFM predictions here we employ a typical GFM, the Fathom model, to a 135,000 km2 region of the Mississippi floodplain in a sensitivity analysis that evaluates how inundated areas and associated population exposures respond when forced with empirically-derived bankfull capacities. Our results show that since the typical RPs (\u003c 1 year) of these present-day bankfull flows differ from the 2-year value normally assumed in GFMs, substantial underestimates of flood extent (9 to 59%, depending on flood magnitude) and populations exposed (15 to 118%) result. We also show that, over multi-decadal timescales, changes in past channel morphology are, depending on emissions scenario, of equal or greater importance in driving changes in simulated flood hazard and risk than changes in future climate. 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