Abstract
Abstract. Flooding is of particular concern in low-lying coastal zones that are prone to flooding impacts from multiple drivers, such as oceanographic (storm surge and wave), fluvial (excessive river discharge), and/or pluvial (surface runoff). In this study, we analyse, for the first time, the compound flooding potential along the contiguous United States (CONUS) coastline from all flooding drivers, using observations and reanalysis data sets. We assess the overall dependence from observations by using Kendall's rank correlation coefficient (τ) and tail (extremal) dependence (χ). Geographically, we find the highest dependence between different drivers at locations in the Gulf of Mexico, southeastern, and southwestern coasts. Regarding different driver combinations, the highest dependence exists between surge–waves, followed by surge–precipitation, surge–discharge, waves–precipitation, and waves–discharge. We also perform a seasonal dependence analysis (tropical vs. extra-tropical season), where we find higher dependence between drivers during the tropical season along the Gulf and parts of the East Coast and stronger dependence during the extra-tropical season on the West Coast. Finally, we compare the dependence structure of different combinations of flooding drivers, using observations and reanalysis data, and use the Kullback–Leibler (KL) divergence to assess significance in the differences of the tail dependence structure. We find, for example, that models underestimate the tail dependence between surge–discharge on the East and West coasts and overestimate tail dependence between surge–precipitation on the East Coast, while they underestimate it on the West Coast. The comprehensive analysis presented here provides new insights on where the compound flooding potential is relatively higher, which variable combinations are most likely to lead to compounding effects, during which time of the year (tropical versus extra-tropical season) compound flooding is more likely to occur, and how well reanalysis data capture the dependence structure between the different flooding drivers.
Highlights
The Contiguous United States (CONUS) comprises 48 states
40 % of population of the United States of America (USA) lives in coastal counties, which make up less than 10 % of the total area of the CONUS; this leads to a high population density relative to inland areas, especially in the 17 major port cities with over 1 million inhabitants located along the USA coast (Hanson et al, 2011)
For the first time, the compound flooding potential that arises from the combination of storm surge, waves, precipitation, and river discharge along the CONUS coastline
Summary
The Contiguous United States (CONUS) comprises 48 states (i.e. all states, excluding Hawaii and Alaska). 40 % of population of the United States of America (USA) lives in coastal counties, which make up less than 10 % of the total area of the CONUS; this leads to a high population density relative to inland areas, especially in the 17 major port cities with over 1 million inhabitants located along the USA coast (Hanson et al, 2011). The coastal counties combined, if they were a single country, would rank third in the world in terms of the gross domestic product (GDP) after the USA and China (NOAA Office for Coastal Management, 2021). 40 % of the people living in coastal counties are at high risk of being affected by coastal flood hazards, including vulnerable populations such as the elderly, children, non-native English speakers, and low-income communities (NOAA Office for Coastal Management, 2021). In the USA, the total direct economic losses from major weather and climate disasters (where each disaster caused a minimum direct loss of USD 1 billion) amounted to Published by Copernicus Publications on behalf of the European Geosciences Union
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