Preprints
https://doi.org/10.5194/hess-2023-31
https://doi.org/10.5194/hess-2023-31
02 Feb 2023
 | 02 Feb 2023
Status: this preprint is currently under review for the journal HESS.

Understanding the Compound Flood Risk along the Coast of the Contiguous United States

Dongyu Feng, Zeli Tan, Donghui Xu, and L. Ruby Leung

Abstract. Compound flooding is a type of flood events caused by multiple flood drivers. The associated risk has usually been assessed using data-based statistical analyses or physics-based numerical models. This study proposes a compound flood (CF) risk assessment (CFRA) framework for coastal regions in the contiguous United States (CONUS). In this framework, a large-scale river model is coupled with a global ocean reanalysis dataset to (a) evaluate the CF exposure risk related to the coastal backwater effects on river basins, and (b) generate spatially distributed data for analyzing the CF hazard risk using a bivariate statistical model of river discharge and storm surge. The two kinds of risk are also combined to achieve a holistic understanding of the continental-scale CF comprehensive risk. The estimated CF risk shows remarkable inter- and intra-basin variabilities along the CONUS coast with more variabilities in the CF hazard risk over the US West and Gulf coastal basins. Different risk assessment methods present significantly different patterns in a few key regions, such as San Francisco Bay area, lower Mississippi River and Puget Sound. Our results highlight the needs to weigh different CF risk measures and avoid using single data-based or physics-based CFRAs. Uncertainty sources in these CFRAs include the use of gauge observations, which cannot account for the flow physics or resolve the spatial variability of risks, and underestimations of the flood extremes and the dependence of CF drivers in large-scale models, highlighting the importance of understanding the CF risks for developing a more robust CFRA.

Dongyu Feng et al.

Status: open (until 30 Mar 2023)

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  • RC1: 'Comment on hess-2023-31', Anonymous Referee #1, 07 Mar 2023 reply

Dongyu Feng et al.

Dongyu Feng et al.

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Short summary
This study assesses the flood risks concurrently induced by river flooding and coastal storm surge along the coast of the contiguous United States using statistical and numerical models. We reveal a few hotpots of such risks, its critical spatial variabilities within a river basin and over the whole US coast, and the uncertainties of the risk assessment. We highlight the importance to weigh different risk measures to avoid underestimating or exaggerating the actual compound flood impacts.