07 Aug 2023
 | 07 Aug 2023
Status: this preprint is open for discussion.

Mangroves as nature-based mitigation for ENSO-driven compound flood risks in a river delta

Ignace Pelckmans, Jean-Philippe Belliard, Olivier Gourgue, Luis Elvin Dominguez-Granda, and Stijn Temmerman

Abstract. Densely populated coastal river deltas are very vulnerable to compound flood risks, coming from both oceanic and riverine sources. Climate change may increase these compound flood risks due to sea level rise and intensifying precipitation events. Here, we investigate to what extent nature-based flood defence strategies, through conservation of mangroves in a tropical river delta, can contribute to mitigate the oceanic and riverine components of compound flood risks. While current knowledge of estuarine compound flood risks is mostly focussed on short-term events such as storm surges (taking one or a few days), longer-term events, such as El Niño events (continuing for several weeks to months) along the Pacific coast of Latin America, are understudied. Here, we present a hydrodynamic modelling study of a large river delta in Ecuador aiming to elucidate the compound effects of El Niño driven oceanic and riverine forcing on extreme high water level propagation through the delta, and in particular, the role of mangroves in reducing the compound high water levels. Our results show that the deltaic high water level anomalies are predominantly driven by the oceanic forcing but that the riverine forcing causes the anomalies to amplify upstream. Furthermore, mangroves in the delta attenuate part of the oceanic contribution to the high water level anomalies, with the attenuating effect increasing in the landward direction, while mangroves have a negligible effect on the riverine component. These findings show that mangrove conservation and restoration programs can contribute to nature-based mitigation, especially the oceanic component of compound flood risks in a tropical river delta.

Ignace Pelckmans et al.

Status: open (until 03 Oct 2023)

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  • RC1: 'Comment on egusphere-2023-1009', Jasper Dijkstra, 11 Sep 2023 reply

Ignace Pelckmans et al.

Ignace Pelckmans et al.


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Short summary
The combination of extreme sea levels with increased river flow typically can lead to so-called compound floods. Often these are caused by storms (< 1 day), but climatic evens such as El Niño could trigger such compound floods over a period of months. We show that the combination of increased sea level and river discharge cause extreme water levels to amplify upstream. Mangrove forests, however, can act as a nature-based flood protection by lowering the extreme water levels coming from the sea.