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Monday, July 20, 2020

Rising Waters, from Central Falls to Charlestown

Climate Crisis Escalates Inland Flood Risk
By ROGER WARBURTON/ecoRI News contributor
The First Street Foundation (FS) model shows an increase in flood risk across Rhode Island. Flooding risks are by zip code. (Roger Warburton/ecoRI News)
The First Street Foundation (FS) model shows an increase in flood risk across Rhode Island. Flooding risks are by zip code. (Roger Warburton/ecoRI News)

Many people who live inland believe that the risks of flooding from hurricanes, sea-level rise, and coastal storms don’t apply to them. Surely, they only impact shoreline properties?

Those assumptions are incorrect.

A new report by the First Street Foundation analyzes the flood risks of every building in the United States. One of the most surprising findings is that there is a much higher risk of inland flooding than previously believed.

The image above illustrates the significant increase in inland flooding risk. The current risk for a substantial flood is defined as a 0.4-inch inundation with a 1 percent annual risk.

Flood risk is traditionally analyzed using the Flood Insurance Rate Map (FIRM) published by the Federal Emergency Management Agency (FEMA). In Rhode Island, FEMA maps identify some 23,900 properties as having substantial flood risk (the left map in image above).

In comparison, the First Street Foundation flood model identifies an additional 9,000 properties as facing this same level of risk (the right map in image above).


The increase in the number of properties at risk is higher because: FEMA hasn’t mapped all areas, as the First Street Foundation has; the foundation’s model includes the impact of small rivers and streams and local storms, which FEMA doesn’t; and the foundation’s model accounts for future environmental considerations, such as increased intensity of storms and sea-level rise, where as FEMA only analyses historical data.

Rhode Island faces year-round floods from tropical storms and hurricanes in late summer and early fall; winter and spring flooding from storms; and spring and fall thunderstorms that produce localized flooding.

The First Street Foundation model estimates that, at present, 10.3 percent of all properties across the contiguous United States have a substantial risk of flooding. That percentage rises to 11.4 percent in 30 years.

At 6.9 percent, Rhode Island has a somewhat smaller proportion of properties at substantial risk today. That percentage rises to 7.9 percent by 2050, the length of a typical mortgage.

In Rhode Island, the First Street Foundation model characterizes 6,600 properties that are facing a 99 percent chance of flooding at least once during the next 30 years. Most concerning is that, of those properties at risk, 61 percent are at major to extreme risk.

The flood risk map for Central Falls and Pawtucket using FloodFactor data. (Roger Warburton/ecoRI News)
The flood risk map for Central Falls and Pawtucket using FloodFactor data. (Roger Warburton/ecoRI News)

Rhode Island cities with the greatest number of properties at risk of flooding.
Rhode Island cities with the greatest number of properties at risk of flooding.

The First Street Foundation’s FloodFactor allows anyone to examine the flood risk of their town, street, or even their individual property.

Providence has the greatest number of properties at risk of flooding, with 5,200 currently at risk, which is about 13 percent of the city’s total number of properties.

Rhode Island locations with the greatest growing risk of properties being flooded.
Rhode Island locations with the greatest growing risk of properties being flooded.

Some Rhode Island municipalities will see a massive increase in flood risk over the next 30 years. Some smaller Rhode Island communities, with fewer properties, have a greater proportion of their properties at risk. Tiverton, for example, will see a 64 percent increase in the number of properties at risk.

A warming Rhode Island will result in rising marine waters, new weather patterns, and more frequent and stronger storms. These factors intensify flooding from hurricanes and storms. They also contribute to deeper floods that cause greater damage from even modest events, such as heavy rains and king tides.

Roger Warburton, Ph.D., is a Newport, R.I., resident.