Mangroves as a protection from storm surges in a changing climate

Study Number

101

Author

Brian Blankespoor, Susmita Dasgupta, Glenn-Marie Lange

Abstract

Adaptation to climate change includes addressing sea-level rise (SLR) and increased storm surges in many coastal areas. Mangroves can substantially reduce vulnerability of the adjacent coastal land from inundation but SLR poses a threat to the future of mangroves. This paper quantifies coastal protection services of mangroves for 42 developing countries in the current climate, and a future climate change scenario with a 1-m SLR and 10% intensification of storms. Findings demonstrate that while SLR and increased storm intensity would increase storm surge areas, the greatest impact is from the expected loss of mangroves. Under current climate and mangrove coverage, 3.5 million people and GDP worth roughly US $400 million are at risk. In the future climate change scenario, vulnerable population and GDP at risk would increase by 103 and 233%. The greatest risk is in East Asia, especially in Indonesia and the Philippines as well as Myanmar.

Main Results and Conclusions

• It is well-documented that mangroves can provide protection along the coast.
  • “Coastal forests belts have the potential to act as bioshields for the protection of people and other assets against above-mentioned coastal hazards.” (479)
• However, the changing climate is likely to affect the degree to which certain mangrove areas will be able to provide protection; some mangrove areas are likely to perform better than others.
  • “…we also find areas benefiting from storm surge attenuation by mangroves vary across countries due to variations in the storm surge height, the extent of mangroves and elevation of the vulnerable zone between countries.” (486)
  • “Our estimates for the 1-in-100 storm surge height for 46 countries with previous exposure to cyclones covered in this study further indicate that extensive mangrove coverage does not always result in wide coastal protection.” (486)
  • “These findings illustrate the importance of careful review of the site selection for mangrove plantation to achieve effective coastal protection, as well as careful consideration in converting existing mangroves to other land uses.” (486)
• The countries surveyed were: China, Fiji, Hong Kong SAR, Indonesia, Macao SAR, Micronesia, Myanmar, Palau, Papua New Guinea, Philippines, Samoa, Solomon Islands, Taiwan (China), Thailand, Timor-Leste, Tonga, Vanuatu, Viet Nam, Antigua and Barbuda, Belize, Colombia, Costa Rica, Cuba, Dominica, Dominican Republic, Grenada, Guatemala, Haiti, Honduras, Jamaica, Mexico, Nicaragua, Panama, Saint Kitts and Nevis, Saint Lucia, Saint Vincent and the Grenadines, Trinidad and Tobago, Rep. Bol. De Venezuela, Bangladesh, India, Pakistan, Sri Lanka, Comoros Islands, Madagascar, Mozambique, and Seychelles.
• The regions surveyed were: East Asia and Pacific, Latin America, South Asia, and Sub Saharan Africa.
• Some countries/regions are more likely to be affected than others by storm intensification, sea level rise, and loss of mangroves.
  • “For the 46 countries considered in this study, the total storm surge inundation area is expected to increase by 31% from 84,222 to 110,218 sq. km, and all the regions will be adversely affected.” (485)
  • “…Latin America and Caribbean are the most affected: the inundation area is expected to increase by 61%.” (485)
  • “increase ranging from Cuba (2%), Bangladesh and Mozambique (4%), Papua New Guinea (6%) to India (71%), and Mexico (173%).” (485)
  • “Among the top ten countries, the population of Indonesia and the Philippines are most at risk under all climate change impacts, but Mexico and Myanmar along with the Philippines will also experience large increases in vulnerability of population and GDP.” (486)
• One of the greatest potential impacts of climate change will be a significant loss of mangroves, driven mostly by SLR.
  • “By 2100, in a changing climate with 1 m SLR, approximately 29% of mangroves are likely to be lost, but 71% may migrate and continue to provide coastal protection.” (488)
  • “Natural migration will be successful only if mangroves are not blocked by other land uses and SLR is not faster than the natural migration rate.” (488)