Hurricane Milton could bring a ‘reverse storm surge’

Depending on where Hurricane Milton makes landfall, the Tampa Bay area could be flooded with a huge storm surge or it could have its bay sucked dry.

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This hurricane season feels different. Early on the government predicted 17 to 25 named storms but only a total of 13 storms have occurred including Milton.  The Atlantic slumbered during an August that produced a 50-year record low in the number of storms. For Rhode Island this has meant virtually no activity – so far. No big storms and no expenses. If that’s the nothing, what is the double?

In those locations where hurricanes have gone ashore this year the double whammy is ocean storm surge combined with heavy rain on land.  To understand how rain plays into this, one has to look no further than the recent floods in Asheville, North Carolina. With one to almost three feet of Helene’s rainfall, areas in the region were swamped.  Since Asheville is over 400 miles and about 2,000 vertical feet from where the hurricane hit land, we can be sure Helene’s water impacts there are rain. Sadly, the currently known 19 deaths in Florida and 115 in North Carolina from Helene as of midweek further emphasize the severity of rain alone as a hurricane hazard.

More: Where to find high water mark plaques from RI’s past floods and hurricanes

Rhode Islanders know about storm surges like the 1938 hurricane that landed nearly 20 feet of seawater in Providence and Hurricane Carol in 1954 which produced over 14 feet. They occurred before the Fox Point Hurricane Barrier was completed in 1966.  However, sea level has risen about half a foot over the lifetime of the barrier according to the Providence tide gauge.  At some point continued sea level rise will mean even past storm surges can top the barrier. 

However, the idea that rainfall can be equally important as ocean storm surge may be new to many.  A warmer atmosphere holds more moisture, and the rain gauge at T.F. Green International Airport reflects this with an increase in annual precipitation of about six inches since the Hurricane Barrier was completed. In a storm situation which produces the need to close the barrier to keep the sea out, pumps are required to move rainwater that has drained to the rivers behind it.  Averages do not predict the impact of a storm which will depend very much on the nature of the event itself, but they indicate a trend that more easily results in flooding.  More rain and rising seas mean that the Fox Point Barrier is in clear need of rejuvenation.

Not only has the average rainfall changed, but when the skies dump on an urban landscape the water flows along the surface with ever greater depth and virulence.  Providence has 37 percent of its area covered by rooftops, roads, sidewalks, and parking lots. Tunnels under the city can store moderate rains but not the results of a hurricane. With more rain and a high percentage of impervious surface in the city, Providence’s hazard mitigation plan quite rightly recognizes that urban flooding is extremely likely.     

More: Breakwaters have protected Galilee from storms for over a century. Now repairs are needed

The numbers and the threat don’t look good, but they also say that a large area of Providence can be a candidate for storing the rain on site or allowing it to sink into the ground. Simple as it seems, this requires institutional changes to incentivize private property owners to participate.  In Providence, strides have been made on public property and when private property is developed or redeveloped with the use of catchment basins and a variety of other management practices. However, incentivizing retrofits of this type on private property requires innovations that many other U.S. cities are investing in like credits to owners to maintain storage and infiltration solutions. Now is the time to bring those innovations here and make them work for Rhode Island.

Rather than owing twice as much or vastly more when our watery bet goes sour, Rhode Islanders should understand the consequences of a hurricane hitting Rhode Island well before it happens. Most importantly let’s act now to hold more rainwater on land and rejuvenate key infrastructure in preparation for the day the rains come. 

Richard Burroughs teaches in the Department of Marine Affairs at the University of Rhode Island. He is a member of the Providence Resilience Partnership.