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Articles
https://doi.org/10.1038/s41893-021-00706-6
1Institute of Marine Sciences, University of California, Santa Cruz, CA, USA. 2Pacific Coastal and Marine Science Center, United States Geological Survey,
Santa Cruz, CA, USA. 3Center for Integrated Spatial Research, University of California, Santa Cruz, CA, USA. ✉e-mail: breguero@ucsc.edu
Tropical storms represent the most common and costliest
natural disasters across the United States and globally1–3.
Communities in low-lying coastal zones are currently some
of the most at risk from natural hazards but also increasingly threat-
ened by rising sea levels4,5, intensifying storms, more powerful
ocean waves6 and expanding coastal development7–9. As storm costs
mount, communities are increasingly looking for effective mea-
sures to protect low-lying coastal communities that do not cause
negative environmental impacts and that can contribute to coastal
sustainability10,11.
Ecosystems such as reefs, beaches, dunes and wetlands
provide an effective first line of defence against these hazards and
represent a promising option to adapt to the increasing climate
impacts12–14. However, these protection services are disappear-
ing as ecosystems continue to be lost at alarming rates globally
from both natural and human pressures15,16. These losses could esca-
late flood risk17 in just years to levels not anticipated by sea-level
rise for decades or a century18. Multilateral agencies (for example,
the World Bank), government agencies (for example, US Army
Corps of Engineers, USACE) and even the insurance industry
increasingly acknowledge the role of ecosystems in reducing losses
and risk13,19 but alignment of hazard mitigation and environmental
management is still widely lacking20. Coral reefs are one of the most
diverse ecosystems but also one of the most effective natural barri-
ers against the impacts of storms14,17,21,22. In the United States, coral
reefs line >3,100 km of the most at-risk coastlines across Florida,
Hawaii and the US Trust Territories. However, recent measure-
ments in Hawaii, Florida and the US Virgin Islands (USVI) indicate
that coral reefs have eroded more than 1 m vertically over the past
decades23. These trends are likely to be exacerbated in the future
due to climate change effects and anthropogenic stressors to coral
reefs24–26.
Coral reef management and restoration can improve reef
health but it will require increasing resources27,28. Funds dedi-
cated to coral restoration and conservation are very limited com-
pared to funding for hazard mitigation, climate adaptation and
storm recovery. In 2018, for example, the United States provided
about US$15 billion for USACE to construct flood and storm dam-
age reduction projects, of which >US$10 billion was dedicated to
States and Territories impacted by hurricanes Harvey, Irma and
Maria29. In comparison, the most ambitious project in reef restora-
tion in the United States, Iconic Reefs in the Florida Keys, proposes
~US$5 million yr–1 (http://go.nature.com/3ceWKx7).
Risk reduction funds could support ecosystem management
goals if the natural coastal protection benefits were valued using rig-
orous approaches required by risk managers. However, few studies
have rigorously addressed the economic value of coastal ecosystems
in reducing damages to coastal communities30. The development of
risk-based valuations of ecosystem-based flood protection has been
limited by the lack of high-resolution data on bathymetry, topog-
raphy, ecosystems and economic assets and the difficulty in mod-
elling complex hydrodynamic processes across large regions. For
these reasons, previous studies do not model flooding directly31,32
or rely on global-scale data and simplified physics-based modelling
approaches17,33. Yet, recent technological and data advances now
make it possible to quantify and directly assess flood losses and
the benefits of coastal ecosystems for reducing them with unprec-
edented rigour and spatial definition.
Here, we considerably advance conventional probabilistic risk-
modelling frameworks17,34,35 to evaluate flood damage for the coral
reef-lined US coasts of the States of Florida and Hawaii and the
Territories of Puerto Rico, USVI, American Samoa, Guam and the
Commonwealth of the Northern Mariana Islands (CNMI). We use
high-resolution data on bathymetry, topography, coral distribution
and cover and socio-economics with state-of-the-art, physics-based
hydrodynamic models that resolve the nonlinear processes of wave
breaking, wave-driven water levels, run-up and coastal flooding at
10-m resolution, across the scale of the nation. Multidecadal wave
and coastal water-level data were used to drive physics-based,
numerical models to quantify the effect of the reefs on nearshore
hydrodynamics and onshore flooding. Water depths and flood
zones were calculated across the coral reef-lined US coasts to deter-
mine the people, number of buildings, direct and indirect economic
impact and critical facilities at risk of coastal flooding. The risk
reduction benefits were calculated as the averted impacts between
present-day coral reefs and a scenario that assumes a 1 m reduction
in reef height, on the basis of historic measurements. These new
approaches and data make it possible to assess the benefits of coral
The value of US coral reefs for flood risk reduction
Borja G. Reguero 1 ✉ , Curt D. Storlazzi 2, Ann E. Gibbs 2, James B. Shope1, Aaron D. Cole3,
Kristen A. Cumming2 and Michael W. Beck 1
Habitats, such as coral reefs, can mitigate increasing flood damages through coastal protection services. We provide a
fine-scale, national valuation of the flood risk reduction benefits of coral habitats to people, property, economies and infrastruc-
ture. Across 3,100 km of US coastline, the top-most 1 m of coral reefs prevents the 100-yr flood from growing by 23% (113 km2),
avoiding flooding to 53,800 (62%) people, US$2.7 billion (90%) damage to buildings and US$2.6 billion (49%) in indirect
economic effects. We estimate the hazard risk reduction benefits of US coral reefs to exceed US$1.8 billion annually. Many
highly developed coastlines in Florida and Hawaii receive annual benefits of over US$10 million km–1, whereas US reefs criti-
cally reduce flooding of vulnerable populations. This quantification of spatial risk reduction can help to prioritize joint actions
in flood management and environmental conservation, opening new opportunities to support reef management with hazard
mitigation funding.
NATURE SUSTAINABILITY | VOL 4 | AUGUST 2021 | 688–698 | www.nature.com/natsustain
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