Map showing 100-year flood areas, areas with a 1 percent chance of a very large flood in any given year, on the coast of Maui, Hawaii. Blue areas denote the areas that would flood during a 100-year storm; the red areas denote the regions that would flood without the presence of coral reefs (marked in gray) and thus are protected by coral reefs. A 100-year flood has a 1 percent chance of happening every year.

Coral Reef Barriers Provide Flood Protection for 18,000 People and $1.8 Billion Worth of Economic Activity Annually

Today, the U.S. Geological Survey (USGS) released the findings of a new, in-depth study titled “Rigorously Valuing the Role of U.S. Coral Reefs in Coastal Hazard Risk Reduction,” – funded in part by the U.S. Department of the Interior’s (DOI) Office of Insular Affairs.

The findings demonstrate annual benefits of coral reefs including a flood-protection barrier for more than 18,000 coastal citizens and $1.8 billion worth of coastal infrastructure in the United States and its trust territories. The study will help managers take effective actions to reduce the risk to, and increase the resiliency of, U.S. mainland and U.S. insular area coastal communities to flooding and other hazards.

“Our Office was glad to collaborate with the USGS and leverage funds available through the Coral Reef and Natural Resources Initiative,” said DOI Insular and International Affairs Assistant Secretary Doug Domenech. “This highlights the important role that coral reefs play not only for coastal communities in the U.S. mainland, but also in the U.S. insular areas. These research results will be of great interest to the U.S. Coral Reef Task Force, a body tasked to lead U.S. efforts on coral reef ecosystems and that the Interior and the Department of Commerce chair jointly.”

“As this study shows, USGS science can help save lives, minimize property damage and reduce risks from natural hazards,” said USGS Director James Reilly. “Information at this fine resolution is critical to coastal managers and planners working on flood mitigation, coastal defense, transportation and hurricane response and recovery from the local to national scales.”

The research, led by USGS research geologist Curt Storlazzi, analyzed flood risk and assessed reef benefits of populated U.S. reef-lined coasts of Hawaii, Florida, American Samoa, Guam, the Commonwealth of the Northern Mariana Islands, Puerto Rico and the U.S. Virgin Islands. It is the first time that scientists have combined real-world computer models of storms and waves with engineering, ecological, mapping and social and economic tools to create detailed, rigorous estimates of the value of coral reef defenses along U.S. mainland and U.S. insular area coastlines both in the long-term (annualized) and for more infrequent events such as 50- or 100-year storms.

The study models can forecast localized threats to people and economic damage in areas with and without coral reefs at a 10-square meter (108 square feet) resolution along more than 3,100 kilometers (1,920 miles) of populated U.S. coral reef-lined shoreline.

Coral reefs, noted Storlazzi, are coastal barriers that can substantially reduce coastal flooding and erosion by reducing the energy of waves as they wash ashore.

“Our goal in this study was to provide sound science to identify where, when and how U.S. coral reefs provide significant coastal flood reduction benefits to ultimately save dollars and protect lives,” said USGS research geologist Storlazzi.  

Underwater, a man wearing a snorkel, fins, and mask swims down to a coral reef with an instrument tied to a tether.
Research geologist Curt Storlazzi free-dives in order to set an instrument on the reef off Kauaʻi, Hawaiʻi in March of 2015.(Credit: Amy West, USGS Science Communications Contractor. Public domain.)

The value of coastal flood risk reduction provided by coral reefs varies from location to location, primarily because of population density and the elevation of coastal areas. For example, coral reefs shield more than 3,300 people on Maui each year but just over 100 on Guam, where most housing and infrastructure is located at higher elevations because of the nearly constant threat of typhoons. Coral reefs annually protect $183 million worth of buildings and economic activity in Puerto Rico, $675 million in Florida and $836 million in Hawaii.

According to Storlazzi, these data indicate that in the event of a 50-year storm (which has a 2 percent chance of occurring in any given year), the economic and protective benefits of coral reefs are even greater. In such a storm, for example, coral reefs off the heavily urbanized coast of Miami-Ft. Lauderdale, Florida, would provide more than $1.6 billion in protection, and off the coast of Honolulu, Hawaii, they would provide more than $435 million in protection.

“This approach represents a massive advance in the precision and resolution of flood risk assessment for ecosystems and in coral reef-lined areas and is an approach that can be applied to other ecosystems, such as coastal vegetation,” said University of California at Santa Cruz (USSC) research scientist Borja Reguero. “In addition, the model can be used to assess the impacts of future changes in storms or sea level.”

The study also calculates the extent to which critical infrastructure, such as hospitals, fire stations, roads and power plants, are protected from coastal flooding by coral reefs.

“We provide clear values of risk and reef benefit to inform key decisions in flood hazard mitigation, storm recovery spending and coral reef management,” said UCSC research professor and former lead marine scientist with The Nature Conservancy Michael Beck.

Background: The new report titled “Rigorously Valuing the Role of U.S. Coral Reefs in Coastal Hazard Risk Reduction,” was conducted by scientists with the USGS, The Nature Conservancy, the University of California at Santa Cruz and Deltares. It was funded by USGS and DOI Office of Insular Affairs.

Department of the Interior,
U.S. Geological Survey

Office of Communications and Publishing
12201 Sunrise Valley Drive
Reston, VA 20192
United States
Phone: 703-648-4460

Pacific Coastal and Marine Science Center