Valuing the Natural Defenses from Coral Reefs and Mangroves

As flood risks rise, engineers, ecologists and economists come together to maximize our first line of defense

I’m a conservation scientist and if you had told me four years ago that my team would have more engineers and economists than ecologists, I would have laughed. But effective conservation requires more than just biology, and today these cross-cutting teams are essential to saving habitats.

Since Hurricane Katrina and the Indian Ocean tsunami struck more than a decade ago, there has been a growing appreciation that coastal habitats play some role in natural defense. And there have been interesting “back of the envelope” calculations of their importance, but these roughed-out values are not sufficient to change decision making.

Public and private sector leaders must regularly assess the costs and benefits of their actions. They need reliable information couched in common currencies to make effective choices. Nature-based solutions have not historically been described in this language. As a result, all too often the value of habitats is deeply discounted in these decisions. And, when we have valued ecosystems, so often we have only valued what we take from habitats, such as fish and timber, and not the benefits that we get if we leave these habitats in place.

But we can properly value conservation in the language decision-makers use; it’s just that we need partners well beyond the traditional conservation community to get there.

Today we might be at a tipping point. The World Bank, joined by a team of collaborators from TNC, University of California (UC) Santa Cruz, UC Davis, UC Santa Barbara, Resources for the Future, and the Science for Nature and People Partnership, has just released new comprehensive Guidelines for Measuring and Valuing the Coastal Protection Services of Mangroves and Coral Reefs. From the evidence in the Guidelines, it is increasingly clear that:

  • Mangroves and coral reefs provide significant coastal protection benefits. Mangroves can reduce wave height by 13 to 66 percent over a 100-meter-wide belt, and by 50 to a full 100 percent over a 500-meter-wide mangrove belt. If mangrove forests are sufficiently large, they can reduce storm surge peak water levels between 4 and 48 cm per kilometer of mangrove. Coral reefs reduce wave energy by up to 97 percent. Healthy reefs can protect coasts even during storms with strong wave conditions.
  • Many countries are already using these natural coastal protection benefits in policy and practice. In Vietnam, for instance, the reforestation of 9,000 hectares of mangroves demonstrated cost-benefit ratios ranging from 3:1 in some communities to as high as 28:1 in others.
  • We can rigorously value the Annual Expected Benefits of natural coastal protection. Drawing from approaches that are commonly used in the insurance and engineering sectors, the Guidelines recommend a rigorous and straightforward approach for valuing the coastal protection benefits of mangroves and reefs (see Figure 1). Moreover, these valuations are doable nationally and globally with existing data as we are showing in the Mapping Ocean Wealth project.
Figure 1: Key steps and data for estimating the flood protection benefits from habitats. (a) Stage 1: oceanographic data are combined to assess the total water levels (TWLs) offshore. Stage 2: TWLs are modified by nearshore hydrodynamics. Stage 3: effects of habitat on TWLs are estimated. Stage 4: TWLs are extended inland along profiles to define flooding envelopes for storm events (e.g., 10, 25, 50, 100-yr events) with and without existing coral reefs. Stage 5: The property damaged under flooding envelopes are estimated. (Figure adapted from World Bank 2016).
Figure 1: Key steps and data for estimating the flood protection benefits from habitats. (a) Stage 1: oceanographic data are combined to assess the total water levels (TWLs) offshore. Stage 2: TWLs are modified by nearshore hydrodynamics. Stage 3: effects of habitat on TWLs are estimated. Stage 4: TWLs are extended inland along profiles to define flooding envelopes for storm events (e.g., 10, 25, 50, 100-yr events) with and without existing coral reefs. Stage 5: The property damaged under flooding envelopes are estimated. (Figure adapted from World Bank 2016).

 

A core concept guiding these efforts is that the valuation of these services can provide a strong incentive for decision-makers to manage these ecosystems better. The United Nations has identified an experimental approach for accounting for ecosystem services in the System of National Accounts, and these new Guidelines from the World Bank provide a clear approach for how natural flood defenses from coral reefs and mangroves can be valued for national accounting and other critical decisions. We would never have arrived at such clear and rigorous guidance without a strong multidiscipline team, and the opportunity to bring them together through the Science for Nature and People Partnership Project (SNAPP).

What’s more, mainstreaming the coastal defense value of mangroves and reefs in policy and management decisions presents critical near-term opportunities, as there are substantial climate and disaster risks that will affect these ecosystems – and the communities that rely on their services – during the next 5 to 10 years.

If decision-makers can make “apples-to-apples” comparisons and see just how effective—and cost-effective—natural habits can be at reducing flood risks, we should see much broader investment in their conservation and restoration. That’s a win for people and for nature.

Mike Beck

Mike Beck is lead marine scientist for The Nature Conservancy and a research associate at the Institute for Marine Science. Beck works on the interface between marine science and… Read More
SNAP