River channel change can affect flood hazard and impact substantially

Hawker, L., Darby, S., Slater, L., Parsons, D., Boothroyd, R., Ashworth, P., Cloke, H. ORCID: https://orcid.org/0000-0002-1472-868X, Delorme, P., Gebrechorkos, S., Griffith, H., Hirabayashi, Y., Leyland, J., Liu, Y., McLelland, S., Nicholas, A., Sambrook Smith, G., Sampson, C., Vahidi, E., Wortmann, M. and Yamazaki, D. (2026) River channel change can affect flood hazard and impact substantially. Communications Earth & Environment. ISSN 2662-4435 (In Press)

Abstract/Summary

Over a billion people are at risk of flooding and this is expected to double by 2050 due to climate change, population growth, and encroachment into at-risk areas. Global Flood Models (GFMs) are vital tools for producing flood hazard maps, supporting key policy interventions. However, GFMs often assume that river bankfull flow capacity corresponds to a fixed return period (RP), of typically two years, which overlooks spatial and temporal variations in channel size, shape, and roughness. To quantify the extent to which channel variability biases GFM predictions we employ a GFM, the Fathom model, in a sensitivity analysis that evaluates how inundated areas and population exposures respond when forced with empirically-derived bankfull capacities. We find that actual RPs of present-day bankfull flows (<1 year) differ substantially from the assumed two-year RP, leading to underestimations of flood extent (9–152%) and exposed populations (15–472%) for the 3 flood return periods analysed (5-year, 20-year and 100-year), with the greatest differences for the more frequent floods. We also show that, over multi-decadal timescales, changes in past channel morphology are comparable to the influence of future climate change in affecting flood impacts, depending on emissions scenarios.

Item Type	Article
URI	https://centaur.reading.ac.uk/id/eprint/129375
Refereed	Yes
Divisions	Science > School of Archaeology, Geography and Environmental Science > Department of Geography and Environmental Science Science > School of Mathematical, Physical and Computational Sciences > Department of Meteorology
Publisher	Springer Nature
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