by Roger Stephenson, Union of Concerned Scientists
Today scores of coastal communities in the United States are seeing more frequent tidal flooding. And as global warming drives sea levels higher over the next 15 to 30 years, flooding from high tides is expected to occur even more often and cause more disruption, particularly on the East Coast and, increasingly, on the Gulf Coast.
Encroaching Tides: How Sea Level Rise and Tidal Flooding Threaten U.S. East and Gulf Coast Communities over the Next 30 Years, a new report from the Union of Concerned Scientists, shows how coastal communities could be affected, and makes recommendations on how they can increase their resilience. Portsmouth is profiled on page 22.
The analysis explores projected changes in tidal flooding under a mid-range scenario of sea level rise, and the implications for East and Gulf Coast communities in the absence of adaptive measures. Over the next 15 to 30 years, the frequency, extent, and duration of tidal flooding could increase substantially in many of the 52 locations we examined. By 2045, within the lifetime of a 30-year mortgage, many coastal communities are expected to see roughly one foot of sea level rise. As that occurs, one-third of the 52 locations in our analysis would start to face tidal flooding more than 180 times a year, on average. Nine locations can expect to see tidal flooding 240 times or more per year. While today this type of flooding is typically considered a nuisance, if it becomes chronic, its impact on local communities would grow. And with sea level rise, some tidal floods are also expected to become much more extensive.
To prepare for these changes, local communities will have to take steps to upgrade built infrastructure, discourage new development in areas that flood more often, and carefully weigh the risks and benefits of adaptation measures. But local communities can't go it alone-coastal challenges are too great, the costs are too steep, and too many people are at risk. Instead, we need a coordinated, well-funded national response to our country's coastal vulnerability involving federal, state, and local collaboration. And while the near-term increase in sea level rise and tidal flood conditions outlined in this report may be locked-in, changes later this century and beyond are not fixed. We can avoid longer-term impacts by taking swift and strong measures to reduce our carbon pollution.
On September 12 the New Hampshire Coastal Risks and Hazards Commission released a report on sea level rise, storm surge and precipitation. The commission requested the report from a Science and Technical Advisory Panel that it formed earlier in the year. The purpose was to ensure that commission members are aware of and using the best available and most relevant scientific and technical information to inform its recommendations to the Governor in 2016.
The report, “Sea-level Rise, Storm Surges, and Extreme Precipitation in Coastal New Hampshire: Analysis of Past and Projected Future Trends” summarizes the varying scientific information on the anticipated future coastal flood hazards attributed to sea level rise (SLR), storm surge, and increased precipitation. The Panel’s report also includes advice on the planning parameters that the Commission should use in framing its recommendations. The conclusions reached by the Panel regarding future coastal flood hazards are consistent with the Third U.S. National Climate Assessment completed in 2013-2014. The New Hampshire report is available here.