Tidal floods driven by climate change may hurt small businesses

WASHINGTON — Sea level rise, driven by climate change, is causing increased flooding during high tides along much of the U.S. coastline. Though such floods are usually minor, a new study suggests that car traffic patterns could help reveal how floods harm an area’s business revenues.

Tidal flooding events “are not one in a hundred years or one in a thousand years. They’re once a week,” says Miyuki Hino, an environmental social scientist at Stanford University.

Though increasingly frequent, such floods often last only a few hours. That can make it hard to tally the economic losses they cause. Hino and her colleagues sought to quantify those impacts by looking at parking data in the historic downtown of Annapolis, Md., located on the Chesapeake Bay. 

The team first built a database of flood events using flood images posted to social media at the same times that tide gauge readings showed high water levels, in order to eliminate rain-caused flooding. Hino’s team estimates there were 44 tidal floods in 2017, classified as minor, modest or severe.

The team then looked at parking transactions in a nearby lot for changes in parking revenues. Flood events coincided with drops in visitation ranging from 37 to 89 percent, depending on the severity of the flooding, the researchers found. That contributed to about 3,000 fewer visitors, or a 1.7 percent decrease, in 2017, according to the study published online February 15 in Science Advances.

While combined 2017 annual revenues for 16 area businesses totaled $12.2 million in 2017, the researchers did not have access to the shops’ daily financials.

So they looked to city data tallying daily revenues at downtown businesses for dates that flooded (defined as moderate to severe on Hino’s scale) in 2016 but not 2015. They found that revenues on those days dropped by 22.5 percent on average.

That let researchers estimate the economic losses caused by flooding’s impact on visitors in 2017. A 1.7 percent drop in annual visitors would have led to between a 0.7 percent and a 1.4 percent loss in revenues for the 16 downtown businesses — or between $86,000 to $172,000, Hino and her colleagues conclude.

Because seas are expected to continue rising in coming decades (SN: 10/27/18, p. 7), such tidal flood losses are likely to increase, says Hino, who also presented the work at a Feb. 14 news conference at the annual meeting of the American Association for the Advancement of Science.

The study is useful in drawing attention to costs and damages from tidal flooding, says Hamed Moftakhari, a civil and environmental engineer at the University of Alabama in Tuscaloosa who was not involved in the study. But the situation beyond a small downtown parking lot is likely to be much more complex than what the study encapsulates, he says. “I would love to see some more comprehensive representation of the cost than just parking lot transactions.”