Higher Sea Level Projections Required Along U.S. Coasts

President Barack Obama issued an executive order on Friday,January 30, 2015, directing federal, state and local agencies to incorporate projections for sea level rise in planning and construction along the coasts.

The new Federal Flood Risk Management Standard requires that all federally funded projects located in floodplains, including buildings and roads, be built to withstand flooding. The requirement, the White House said in a release Friday, would “reduce the risk and cost of future flood disasters” and “help ensure federal projects last as long as intended.”

“It is the policy of the United States to improve the resilience of communities and Federal assets against the impacts of flooding,” the order states. “These impacts are anticipated to increase over time due to the effects of climate change and other threats. Losses caused by flooding affect the environment, our economic prosperity, and public health and safety, each of which affects our national security.”

According to the National Oceanic and Atmospheric Administration (NOAA), the U.S. can expect to see up to two feet of sea level rise by the end of the century, largely due to climate change. Warmer temperatures are causing thermal expansion in the oceans, as well as the melting of sea ice, which is pushing sea levels higher globally. A study from the U.S. Geological Survey found that half of the U.S. coastline is at high or very high risk of impacts due to sea level rise.

This is a significant shift, as agencies have typically used historic information on sea level and flooding for planning, rather than future projections. The order directs agencies to use the “best-available, actionable hydrologic and hydraulic data and methods that integrate current and future changes in flooding based on climate science” when evaluating what is in the flood plain. They also have the option of building 2 feet above current base flood elevations for “non-critical” infrastructure and 3 feet above for “critical” infrastructure, or building to the standard of the 500-year flood (a flood with an estimated 0.2 percent chance of happening in any given year).

The Task Force on Climate Preparedness and Resilience released a set of recommendations last November, and establishing this type of guideline was among them. Most coastal regions of the United States will see 30 or more days of flooding by 2050 as a result of sea level rise, according to NOAA predictions.

NOAA’s researchers looked at the anticipated frequency of what the National Weather Service considers nuisance flooding, which are floods that are 1 to 2 feet over the regular local high tide and are enough to cause problems but not pose active threats to human life. Some areas of the U.S. are already seeing increased flooding, the researchers said, and it’s only going to get worse.

“Coastal communities are beginning to experience sunny-day nuisance or urban flooding, much more so than in decades past. This is due to sea level rise,” William Sweet, an oceanographer at NOAA’s Center for Operational Oceanographic Products and Services and the report’s coauthor, said in a statement. “Unfortunately, once impacts are noticed, they will become commonplace rather quickly.”

The research was published in the American Geophysical Union’s peer-reviewed online journal Earth’s Future. The projections are based on data from NOAA tidal stations with at least a 50-year continuous record. Warming global temperatures cause thermal expansion of the oceans and also melt ice sheets, leading to sea level rise. The researchers also note that while much of the rise is fueled by climate change, there are parts of the country where the land is sinking as well, adding to the challenge.

The low-end expectations for sea level rise from the researchers’ analysis project a 1.5 feet increase by 2100. Sweet said that within 30 to 40 years even that low-end projection would increase flooding in many areas “to a point requiring an active and potentially costly response.” And by the end of the century, Sweet said, “there will be near-daily nuisance flooding in most of the locations that we reviewed.” The high-end projections of sea level rise they looked at would put the increase much higher, at 4 feet.

Among the places that can expect flooding sooner rather than later, according to the study: Boston, New York City, Philadelphia, Baltimore, the District of Columbia, San Diego and San Francisco.