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Dependence between high sea-level and high river discharge increases flood hazard in global deltas and estuaries

Dependence between high sea-level and high river discharge increases flood hazard in global deltas and estuaries
Dependence between high sea-level and high river discharge increases flood hazard in global deltas and estuaries
When river and coastal floods coincide, their impacts are often worse than when they occur in isolation; such floods are examples of ‘compound events’. To better understand the impacts of these compound events, we require an improved understanding of the dependence between coastal and river flooding on a global scale. Therefore, in this letter, we: provide the first assessment and mapping of the dependence between observed high sea-levels and high river discharge for deltas and estuaries around the globe; and demonstrate how this dependence may influence the joint probability of floods exceeding both the design discharge and design sea-level. The research was carried out by analysing the statistical dependence between observed sea-levels (and skew surge) from the GESLA-2 dataset, and river discharge using gauged data from the Global Runoff Data Centre, for 187 combinations of stations across the globe. Dependence was assessed using Kendall’s rank correlation coefficient (τ) and copula models. We find significant dependence for skew surge conditional on annual maximum discharge at 22% of the stations studied, and for discharge conditional on annual maximum skew surge at 36% of the stations studied. Allowing a time-lag between the two variables up to 5 days, we find significant dependence for skew surge conditional on annual maximum discharge at 56% of stations, and for discharge conditional on annual maximum skew surge at 54% of stations. Using copula models, we show that the joint exceedance probability of events in which both the design discharge and design sea-level are exceeded can be several magnitudes higher when the dependence is considered, compared to when independence is assumed. We discuss several implications, showing that flood risk assessments in these regions should correctly account for these joint exceedance probabilities.
1748-9326
1-12
Ward, Philip J.
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Couasnon, Anais
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Eilander, Dirk
01cd09ca-8639-4cd2-9acd-67c874298a0e
Haigh, Ivan
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Hendry, Alistair
42b38e3f-9651-4c7e-bce1-64816b0eb103
Muis, Sanne
d73531db-78f1-4f65-b1a0-f96ae1c46377
Veldkamp, Ted I.E.
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Winsemius, Hessel C.
0934e633-e76e-4dfa-ad4a-2839fbe60f3a
Wahl, Thomas
fbac2b37-5fd8-41d1-85b1-024e9f61ff34
Ward, Philip J.
ff039336-2f71-44da-b28f-feab4875a944
Couasnon, Anais
3cd73383-6489-4baa-914f-1fd4ff4da620
Eilander, Dirk
01cd09ca-8639-4cd2-9acd-67c874298a0e
Haigh, Ivan
945ff20a-589c-47b7-b06f-61804367eb2d
Hendry, Alistair
42b38e3f-9651-4c7e-bce1-64816b0eb103
Muis, Sanne
d73531db-78f1-4f65-b1a0-f96ae1c46377
Veldkamp, Ted I.E.
644baba8-7d4c-4847-8ef5-71703e8c0b0a
Winsemius, Hessel C.
0934e633-e76e-4dfa-ad4a-2839fbe60f3a
Wahl, Thomas
fbac2b37-5fd8-41d1-85b1-024e9f61ff34

Ward, Philip J., Couasnon, Anais, Eilander, Dirk, Haigh, Ivan, Hendry, Alistair, Muis, Sanne, Veldkamp, Ted I.E., Winsemius, Hessel C. and Wahl, Thomas (2018) Dependence between high sea-level and high river discharge increases flood hazard in global deltas and estuaries. Environmental Research Letters, 13 (8), 1-12, [084012]. (doi:10.1088/1748-9326/aad400).

Record type: Letter

Abstract

When river and coastal floods coincide, their impacts are often worse than when they occur in isolation; such floods are examples of ‘compound events’. To better understand the impacts of these compound events, we require an improved understanding of the dependence between coastal and river flooding on a global scale. Therefore, in this letter, we: provide the first assessment and mapping of the dependence between observed high sea-levels and high river discharge for deltas and estuaries around the globe; and demonstrate how this dependence may influence the joint probability of floods exceeding both the design discharge and design sea-level. The research was carried out by analysing the statistical dependence between observed sea-levels (and skew surge) from the GESLA-2 dataset, and river discharge using gauged data from the Global Runoff Data Centre, for 187 combinations of stations across the globe. Dependence was assessed using Kendall’s rank correlation coefficient (τ) and copula models. We find significant dependence for skew surge conditional on annual maximum discharge at 22% of the stations studied, and for discharge conditional on annual maximum skew surge at 36% of the stations studied. Allowing a time-lag between the two variables up to 5 days, we find significant dependence for skew surge conditional on annual maximum discharge at 56% of stations, and for discharge conditional on annual maximum skew surge at 54% of stations. Using copula models, we show that the joint exceedance probability of events in which both the design discharge and design sea-level are exceeded can be several magnitudes higher when the dependence is considered, compared to when independence is assumed. We discuss several implications, showing that flood risk assessments in these regions should correctly account for these joint exceedance probabilities.

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Ward 2018 Environ Res Lett 13 084012 - Version of Record
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More information

Accepted/In Press date: 17 July 2018
e-pub ahead of print date: 30 July 2018
Published date: 2018

Identifiers

Local EPrints ID: 424363
URI: http://eprints.soton.ac.uk/id/eprint/424363
ISSN: 1748-9326
PURE UUID: 2f802cc0-a740-4ce8-a6f2-396697a70f69
ORCID for Ivan Haigh: ORCID iD orcid.org/0000-0002-9722-3061

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Date deposited: 05 Oct 2018 11:36
Last modified: 24 May 2022 01:38

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Contributors

Author: Philip J. Ward
Author: Anais Couasnon
Author: Dirk Eilander
Author: Ivan Haigh ORCID iD
Author: Alistair Hendry
Author: Sanne Muis
Author: Ted I.E. Veldkamp
Author: Hessel C. Winsemius
Author: Thomas Wahl

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