Compound Flooding

Compound flooding might not be a new term, but it is fairly new to me. It is only in the last couple of months that I have seen it referred to in professional writings and just the other night on national television news.

Here’s the definition and a weblink.

“The impacts of flooding transcend geospatial boundaries and is the most severe of natural disasters, accounting for billions in damages every year in the United States. During 2022 Atlantic Hurricane Season, the National Oceanic and Atmospheric Administration (NOAA) reported an estimated of $56.65 billion in damages with Hurricane Ian tied for the 5th strongest U.S. landfalling hurricane (155 mph), 7th costliest (estimate >$50 billion), and deadliest Florida hurricane since 1935 Labor Day hurricane.

The risk to citizens, built, and natural infrastructure due to flooding are projected to increase in the future due to the impacts of climate change, including increasing frequency and severity of storms and changing relative sea levels. Much of flood risk reduction planning of the past has relied on a single model that accounts for either rainfall, storm surge, high tides, or other flooding factors. However, many times the causes of flooding combine one or more of these factors resulting in larger impact areas and higher damage costs than were forecast.

Coastal areas are exposed to various ways of flooding, including storm surge, high tides, rainfall, and elevated river flow. The occurrence of two or more of these flood mechanisms is referred to as compound flooding. Observations during numerous flood events along the Gulf of Mexico and Atlantic coastlines have demonstrated that the extents and depths of flooding due to compound flooding can be more severe than flooding due to a single flood mechanism. Consequently, the ability to understand the interplay between the various flooding mechanisms and their impact on flood depths and extents is vital for mitigation planning and design, assessment of impacts to the natural and built environment, and for pre and post disaster response.”

The most recent example of compound flooding has been happening in the State of Florida this week. Even without a hurricane or tropical storm, they have been getting drenched with a series of rainstorms with multiple inches of rain per hour and then also water bubbling up through the sewer/drainage systems. Thus—compound flooding!

Lastly, I see all those cars in Florida becoming submerged in surface water flooding and think about those becoming insurance losses—and, potentially sold again on used car lots. Beware of buying a previously flooded automobile!