The effect of surge on riverine flood hazard and impact in deltas globally

The effect of surge on riverine flood hazard and impact in deltas globally

Eilander, Dirk (Vrije Universiteit Amsterdam; Deltares)
Couasnon, A.A.O. (Vrije Universiteit Amsterdam)
Ikeuchi, Hiroaki (Ministry of Land, Infrastructure, Transport and Tourism, Kyoto)
Muis, Sanne (Vrije Universiteit Amsterdam; Deltares)
Yamazaki, Dai (University of Tokyo)
Winsemius, H.C. (TU Delft Water Resources; Deltares)
Ward, Philip J. (Vrije Universiteit Amsterdam)

2020

Current global riverine flood risk studies assume a constant mean sea level boundary. In reality high sea levels can propagate up a river, impede high river discharge, thus leading to elevated water levels. Riverine flood risk in deltas may therefore be underestimated. This paper presents the first global scale assessment of the joint influence of riverine and coastal drivers of flooding in deltas. We show that if storm surge is ignored, flood depths are significantly underestimated for 9.3% of the expected annual population exposed to riverine flooding. The assessment is based on extreme water levels at 3433 river mouth locations as modeled by a state-of-The-Art global river routing model, forced with a multi-model runoff ensemble and bounded by dynamic sea level conditions derived from a global tide and surge reanalysis. We first classified the drivers of riverine flooding at each location into four classes: surge-dominant, discharge-dominant, compound-dominant or insignificant. We then developed a model experiment to quantify the effect of surge on flood hazard and impacts. Drivers of riverine flooding are compound-dominant at 19.7% of the locations analyzed, discharge-dominant at 69.2%, and surge-dominant at 7.8%. Compared to locations with either surge-or discharge-dominant flood drivers, locations with compound-dominant flood drivers generally have larger surge extremes and are located in basins with faster discharge response and/or flat topography. Globally, surge exacerbates 1-in-10 years flood levels at 64.0% of the locations analyzed, with a mean increase of 11 cm. While this increase is generally larger at locations with compound-or surge-dominant flood drivers, flood levels also increase at locations with discharge-dominant flood drivers. This study underlines the importance of including dynamic downstream sea level boundaries in (global) riverine flood risk studies.

compound flooding
flood impact
flood modelling
flood hazard
model coupling

http://resolver.tudelft.nl/uuid:037352d8-d038-4bcd-8fed-2cb7816bd312

https://doi.org/10.1088/1748-9326/ab8ca6

1748-9318

Environmental Research Letters, 15 (10), 1-12

Institutional Repository

journal article

© 2020 Dirk Eilander, A.A.O. Couasnon, Hiroaki Ikeuchi, Sanne Muis, Dai Yamazaki, H.C. Winsemius, Philip J. Ward