Introduction

Recurring flooding at a waterfront park in the City of Providence was a tip off to Rhode Island coastal resource managers that something was going on. The city having to close its hurricane gates numerous times a year to keep its riverfront walkways dry in the face of high tides pointed to a problem that the city couldn’t afford to ignore.

Waterplace Park in downtown Providence, Rhode Island. Photograph courtesy of Loodog, Wikimedia Commons.

Coastal managers didn’t have to look any further than tidal records to identify the source of the trouble: long-term data from tide gauges showed an increase in average sea level of almost a foot since 1929. Other evidence implicating sea level rise as the root of the problem included local erosion rates that had doubled from 1990 to 2006 and some freshwater wetlands near the coast that were transitioning to salt marsh.

Though the waterfront park’s flooding was limited in scale, its implications for the future were troublesome. With $2 billion invested in developments on the waterfronts in Providence, East Providence, and Pawtucket, coastal managers knew they needed to meet the problem head on.

“Sea level rise is a big issue—a major issue—for us,” says Grover Fugate, executive director of the Rhode Island Coastal Resources Management Council, NOAA’s partner agency tasked with implementing the National Coastal Zone Management program in the state. “We’re already starting to see the impacts of rising water levels along our waterfronts.”

Relative sea level rise as measured by Newport tide gauge. Adapted from J. Boothroyd, University of Rhode Island.

Sea level rise refers to the observed increase in global mean sea level over time. In 2007, the Intergovernmental Panel on Climate Change (IPCC) projected that global sea levels would rise from 7 to 23 inches in the coming century. Since 1990, however, sea level has been rising faster than the rate predicted by models used to generate IPCC estimates.

Future sea level rise is not expected to be uniform around the world, notes Pam Rubinoff of Rhode Island Sea Grant, a program of the National Oceanic and Atmospheric Administration (NOAA). Global sea level affects local sea level, but the location of the water line along any coast also depends upon the shape of the ocean floor, proximity to ocean currents, and regional subsidence or uplift of land.

In Rhode Island, long-term records from the Newport tide gauge show that relative local sea level has risen 10.1 inches (plus or minus 1.2 inches) over the last century. A recent coastal council science report estimates that Rhode Island’s land surface is subsiding by about six inches per century. The difference between the two observations represents the change attributable to global sea level rise.