Dependence between Drivers of Compound Flooding around the Contiguous United States Coastline

Abstract:

Low-lying coastal zones are prone to flooding from multiple drivers: oceanographic (storm surge and wave), fluvial (excessive river discharge), and/or pluvial (surface runoff). The consequences can be exacerbated – depending on local characteristics – when flooding from these drivers occurs in close succession or concurrently and results in extreme events known as ‘compound flooding’. A few studies investigated the dependence between surge and precipitation and between surge and river discharge at different locations along the contiguous United States (CONUS) coastline. However, no comprehensive analysis has been conducted for the dependence between all four main compound flooding drivers: surge, wave, precipitation, and river discharge.

In this study, we carry out a continental scale analysis for the CONUS coastline to characterize and map dependence between the four main compound flooding drivers. We also investigate if this dependence is different between tropical and extratropical seasons. In a final step we assess how dependence varies with time at locations with sufficiently long overlapping records. We carry out the analysis using observations (gauge records) and modeled data (hindcast and state-of-the-art reanalysis databases with homogenous forcing (ERA5)). Dependence between different pairs is assessed using co-occurrence of annual maxima events and statistical measures for dependence (Kendall’s rank correlation coefficient, Spearman’s rank correlation coefficient, and tail dependence coefficients). The dependence structures (in particular of the tails of bivariate distributions) are compared between observations and modeled datasets considered here.

This analysis provides a comprehensive characterization of compound flooding potential at locations around the CONUS coastline. This will provide insights on where compound flooding needs to be incorporated in flood risk assessment studies to avoid underestimation of flood risk at these locations.