The number of small floods in Southern California and coastal cities around the country is growing, researchers say.
A study published in "Earth's Future," by researchers from the University of California, Irvine this week found that, due to climate change and rising sea levels, more "nuisance" floods are damaging cities such as New York, Miami and Los Angeles. These floods carry with them a potentially enormous price tag for unprepared residents. With time, they could collectively cost us more than extreme, but rare, weather events such as tropical storms or wildfires.
But how much could they cost exactly?
It's too soon to say, Amir AghaKouchak, an associate professor at UCI and co-author of the study, told KPCC.
In 2016, four major flooding events across the United States caused more than $1 billion in damages each, according to the National Oceanic and Atmospheric Administration. In contrast to those 4 major events, UC Irvine's study focuses on much smaller floods that might never make the news.
Hence, the name "nuisance" floods, said AghaKouchak.
“These diffuse floods happen multiple times a month or year,” he said. “They don’t kill anyone, they don’t damage buildings, but over time they have extremely high-cost outcomes, and it happens without us realizing it.”
Before coming to their results, the study's four co-authors examined decades of flood records from 11 cities along the east and west coasts. After comparing each city's flood data with theoretical traffic delays, business and road repair costs, they located nuisance flooding hot spots. These were places where the cost of cleaning up after frequent small floods could begin to outweigh the costs of extreme weather events, said AghaKouchak.
“All of these smaller things – things that accumulate 200-300 hours of damages and closures per year – they add up," said AghaKouchak.
The five cities most affected by nuisance flooding were New York, N.Y., Washington, D.C., Miami, Fla., San Francisco, and Seattle, Wash., according to the study. From these findings, the researchers hope to determine "adaptation measures," for those cities and other areas that are vulnerable to changing sea levels, said Brett Sanders, a co-author of the study.
Here's an example of what nuisance flooding looks like. From Agoura Hills during SoCal's most recent storm:
Flooding records from the National Oceanic and Atmospheric Administration and Climate Central were the main sources of data used in the study, said AghaKouchak. In all, the researchers examined the 11 cities shown below:
The cumulative, "high cost impacts" of nuisance floods are difficult for politicians and city emergency response departments to account for, said AghaKouchak. In the study, the researchers found individual nuisance floods happened frequently in all of the coastal cities they examined, and each flood might only inflict several hundred dollars worth of damage at a time, he said.
Nuisance floods cause a ripple effect in communities, according to the UC Irvine study:
"More immediately, nuisance flooding forces municipalities to expend resources to pump water out of streets. Communities suffer school closures, traffic interruptions, and reverberating waves of cost and inconvenience. Degraded sewer infrastructure results in heightened public health risks."
Local utility companies such as Southern California Edison and LADWP have protocols for dealing with small power outages and traffic issues caused by floods, according to spokespeople from both organizations. But both told KPCC that their organizations do not release the financial costs associated with individual pumping and repairs after less-severe floods.
Residents of flood-prone regions should be aware of the costs associated with nuisance flooding, Hamed Moftakhari, the study's lead author, said in a statement. That way, they can take actions that protect their buildings and roads.
But, he acknowledged, that's easier said than done.
“In a recent social science survey, people weren’t really interested in knowing the depth of the water," he said. "They just wanted to know how long they would be flooded. Their main concern was finding out when they could get back to their schools and businesses.”
In the future, the authors hope to use the study to make sure communities can be better prepared for more frequent flooding, said AghaKouchak.