The Value of Mangroves for Reducing Flood Damages to Coastal Communities

Coastal communities of the global south are highly vulnerable to impacts of climate change, due to high exposure to climate related risks and lack of coping strategies. Very often coastal fishing communities are among the poorest in terms of relative poverty and local governments do not have appropriate risk management strategies in place.

Mangroves and other coastal habitats can play important roles in defending coastline and protecting lives and livelihoods, but it requires rigorous quantification of these benefits to present a compelling case for investment in protection of these natural defenses. This is why in 2016 The Nature Conservancy teamed with the World Bank and scientists from the public, private and academic sectors to identify how to rigorously value the flood protection benefits from coastal habitats. We valued this ecosystem service by adopting tools and from the engineering, risk and insurance sectors and following an Expected Damage Function (EDF) approach. This approach assesses the difference in flooding and flood damages with and without coastal habitats such as mangroves across the entire storm frequency distribution (e.g., 1-in-10, -25 and -100 year storms). This same approach would be used for cost benefit assessment of grey infrastructure against coastal storm surge protection.

Working together with the Institute of Environmental Hydraulics at the University of Cantabria „IH Cantabria„, we then tested this approach with the government of the Philippines to value the benefits of mangroves across that nation. We found that without mangroves the annual flood impacts to people and property would increase by ~25% in particular affecting some of the most socially vulnerable communities.

Now in a first study, we have applied these approaches to mangroves globally  – i.e., across more than 115 nations and 700,000 kilometers of coastline – with support from the German International Climate Initiative.

Mangroves around the world are protecting millions of people, and several billion dollars’ worth of property from flooding every year. The results of our work show the significant effect that mangrove presence has on coastal flooding extents and damages, both from extreme tropical cyclones and from more ‘every day’ events. If today’s mangroves were lost, 18 million more people would be flooded every year, an increase of more than 39%. The annual damages to property would increase by 16% and US $82 billion. In Vietnam, India and China alone, mangroves today protect over 12 million people from flooding. Together with the United States and Mexico, these countries currently save US $57 Billion in damages to residential and industrial property every year thanks to the mangroves they still have. We also find that, in general, the proportional effect of mangroves is higher for the less extreme, more frequent flood events. If mangroves were lost, 32% more people would be flooded by 1- in-10 year events, whereas 16% more people would be flooded by 1-in-100 year events.

We also worked with the Bündnis Entwicklung Hilft, an alliance of German-based humanitarian aid groups, to combine our information on (flood) exposure reduction with estimates of vulnerability from their WorldRiskIndex to identify the countries where mangroves might have the greatest benefits for overall risk reduction. These analyses highlight the importance of mangroves for countries across western and south eastern Africa including Guinea, Mozambique, Guinea­Bissau, Sierra Leone and Madagascar.

These results illustrate how our natural ecosystems are often more valuable to us than we realize and that conserving them will directly benefit both people and nature. Between 1980 and 2005, 19% of the world’s mangroves were lost, resulting in increasing exposure to coastal hazards due to development and increasing vulnerability due to a loss of coastal protection. Conventional approaches to defending the coastline tend to focus only on built infrastructure, neglecting the potential to conserve natural habitats for their coastal defense value. Our studies aim to change that dynamic and show the tremendous value of keeping our mangroves and other coastal habitats in place for our own defense.

We are now working with the insurance industry, including firms such Swiss Re and Munich Re to develop innovative financing tools to support coastal habitat restoration based on their risk reduction benefits. As we can provide quantitative evidence that coastal ecosystems can reduce the total cost of risk, this opens discussions to consider a “resilience dividend” through upfront resilience building measures such as coastal habitat restoration. This is a very innovative approach, and while we have made tremendous progress in aligning ecosystem-based adaptation values with the insurance mathematics, it is still a huge remaining challenge to find the market demand in those vulnerable nations of the global south, who would mostly benefit from mangrove restoration.

Michael W. Beck is Lead Marine Scientist for The Nature Conservancy and a Research Professor at the University of California Santa Cruz
Kerstin Pfliegner is Climate Risk and Resilience Advisor for The Nature Conservancy in Europe
Siddharth Narayan is a Research Scientist at the University of California Santa Cruz