Blue-Sky Floods Take a Rising Toll for Businesses

(Bloomberg) -- When American colonists planned downtown Annapolis, Maryland in 1695, they wanted easy access to the sea. Almost 325 years later, the sea is now closer than ever. It’s so close, in fact, that 16 small businesses lost roughly 2 percent of their revenue in 2017.

In a first-of-its-kind study, Stanford University and Naval Academy researchers looked at the effect of sea-level rise on a single city-block. Specifically, they examined sunny-day floods—inundation that occurs when infrastructure built for lower waters is no longer sufficient to keep back the highest tides—at a central parking lot at City Dock.

As sea levels rise, these “nuisance floods” are becoming more common. From the 1950s to the early 2000s, the days of flooding in the 27 most vulnerable cities across the U.S. grew from two per year to nearly 12. 

The combination of rising seas and sinking coastlines in Annapolis makes the problem far worse. From 1956 to 1960, the city averaged 2.8 days of sunny-day flooding. From 2006 to 2010, it averaged 34.4 days per year. 

To calculate the business costs of this kind of flooding, researchers compiled data from a variety of sources, including the local tidal gauge, weather records, social media posts, police video, parking lot receipts and interviews with local officials. Parking records gave them an hour-by-hour measure of how water affected business activity, which they controlled for various factors, such as time, date and weather, to isolate how many customers stayed away when the waters rose. (The data do not include flooding that occurred outside of business hours, when the parking lot was open.) Local business records provided revenue data on the 16 stores and restaurants closest to City Dock.

Minor floods reduced visits to City Dock by 37 percent, moderate floods by 64 percent and major ones by up to 89 percent. All told, researchers concluded that sea-level related flooding cost the local businesses nearly 2 percent of their revenue in 2017, or as much as $172,000.

Even a steadily rising sea leads to exponential growth in flooding, the data show. Another foot of sea-level rise—roughly the amount Annapolis has seen since 1950—could result in a 25 percent drop in visits to City Dock, as well as other economic and market activity. 

“This is an extremely creative case study,” said Solomon Hsiang, a visiting scholar at Stanford’s Center on Food Security and the Environment. He wasn’t involved in the study, but pointed out that it’s one of the first of its kind to “highlight how subtle and gradual changes in the climate have already begun to impact the everyday lives of many people in the U.S.”

Sea-level rise is causing parking lots and other urban infrastructure to lose their value faster than they otherwise would have, Hsiang said. Annapolis is working with federal and state agencies to protect its historic center, which still has the footprint of its original late 17th-century plan. The city is set to make improvements to drainage, pumps, generators and a seawall. Five years of design, upgrades and construction are expected to cost $12.7 million. 

“We know other cities, like Norfolk and Miami, are facing similar challenges," said Mayor Gavin Buckley. "Here in the city of Annapolis we’re working toward solutions.”

The team is working on applying their methods to other areas, but it’s not easy. “We don’t have a good record of exactly what is flooding when, and we need to be able to measure impacts on the very short time frame of these high-tide floods,” lead author Miyuki Hino said by email.

Climate experts in the region are gradually seeing the projections from their research come to life.

“I personally have to traverse the area that’s most affected by the flooding to get from my home to where I work,” said Donald Boesch, a marine science professor and president emeritus of the University of Maryland Center for Environmental Science. The paper’s sea-level and nuisance-flood projections match climate updates Boesch’s group performs for the state every five years. 

“It’s a real issue,” he said of the flooding. “It’s not all that uncommon anymore.”

To contact the editor responsible for this story: Janet Paskin at jpaskin@bloomberg.net

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