According to the latest report from the World Bank group Accounting and Valuation of Ecosystem Services (WAVES) program, the value of coral reefs and mangroves as ‘green infrastructure’ is not currently being fully recognised in the way that it should. Green infrastructure is essentially natural infrastructure as opposed to ‘grey infrastructure’, which is man-made.

Coral reefs and mangroves are being degraded and their basic survival threatened around the world

Coral reefs and mangroves are being degraded and their basic survival threatened around the world, according to the program’s technical report entitled ‘Managing Coasts with Natural Solutions’. Trends in habitat loss will continue unless these habitats are taken into account in policy and management decisions. As coastal development increases, the total investment in coastal infrastructure and the potential loss of more coastal habitats will continue.

The WAVES program is a global partnership. This partnership aims to promote sustainability by putting natural capital at the forefront of development planning and national economic accounting systems. Other parties in the partnership include Governments, United Nations agencies, non-Governmental organisations (NGOs) and academics. Natural capital accounts are currently being established in Botswana, Colombia, Costa Rica, Guatemala, Indonesia, Madagascar, the Philippines and Rwanda. Many other countries are expected to join the program in the next two years.

Natural events such as flooding, coastal inundation and extreme weather events affect hundreds of millions of vulnerable people, critical infrastructure, tourism and trade around the world. In the last decade, insurers have paid out more than $300 billion to repair damage to coastlines from storms. Typically, such payouts are put towards rebuilding similar coastal infrastructure that is ultimately still vulnerable to coastal storms and flooding.

Coral reefs provide natural protection from flooding and erosion by reducing and dispersing wave energy by up to 97%. They supply and trap sediment found on beaches. Coral reefs also produce carbonates as they grow and if they remain healthy, could require minimal maintenance funding in order to continue to protect coastlines. Mangroves provide food and timber products as well as reducing the risks from coastal hazards. They can reduce wave heights significantly depending on the mangrove width, water depth and topography. Mangroves can also reduce storm surge flooding.

In the United States the Federal Emergency Management Authority (FEMA) spends $500 million each year to reduce flooding hazards. Brazil, China and Columbia are spending billions of dollars addressing the risks of flooding and other climate change related disasters. The majority of these funds are being spent on the construction of infrastructure such as seawalls.

Process-based approaches are the best for valuing the coastal protection services that coral reefs and mangroves provide

According to the ‘Managing Coasts with Natural Solutions’ report, process-based approaches are the best for valuing the coastal protection services that coral reefs and mangroves provide. Process-based approaches use variables including storm surges, currents, sediment transport, and interactions between waves and structures to assess risks and the value of habitats in reducing flooding and other climate change related disasters. The report outlines five steps for estimating the benefits that coral reefs and mangroves provide:

  • Estimating offshore hydrodynamics

In order to estimate offshore dynamics, it is important to first understand the oceanographic conditions that generate waves from wind in deep waters. An assessment of wind, waves, mean sea level, tides and storm surge is critical to understanding offshore hydrodynamics. The average and extreme offshore conditions for each of these variables must be assessed

  • Estimating nearshore hydrodynamics

Waves change as they travel from deep to shallow water as a result of the local bathymetry (e.g. depth profile) and coastal morphology (structural features). In nearshore environments, waves undergo refraction, dissipation, diffraction and other sources of energy transfer. Characterising nearshore wave height and energy is an important part of estimating nearshore dynamics

  • Estimating the effects of coastal habitat on hydrodynamics

Nearshore waves interact with habitats and other structures that attenuate (e.g. weaken) the waves and thereby reduce their energy. Coral reefs attenuate short waves (e.g. wind waves) as the waves break on them. Mangroves can attenuate short and long waves (e.g. storm surges)

  • Estimating flooding

After waves pass over habitats, any remaining wave energy creates onshore flooding or erosion. A key part of assessing the risk of flooding is understanding the frequency of storms in the area. Following an assessment of the storm frequency, it is important to understand topographic elevation as lower lying areas will be more susceptible to flooding. The dimensions of the low lying area in which the flood occurs is defined as the ‘flooding envelope’

  • Assessing expected and averted damages

Assessing these damages involves calculating the number of people and assets within the flooding envelope. Once this is known, a damage function that describes the likely value of assets flooded under different storm frequencies (e.g. one in 10, and one in 100 year events) can be derived. Once this is derived, the difference in damages with and without coral reefs and mangroves can be calculated. This difference is the value of coral reefs and mangroves

Read the WAVES Report here

In reflecting on the World Bank report, I realised that I had previously only thought of coral reefs and mangroves in terms of the marine life that rely on them for survival and the economic value of the tourism they bring. This report has highlighted the need for coral reefs and mangroves to be appropriately valued for the protection they provide for coastal areas in addition to being protected to maintain habitats for the marine life that rely on them.

Including coral reefs and mangroves as part of a region’s green infrastructure not only attributes a realistic value to these areas in terms of their value to marine life and tourism but also demonstrates why their conservation must be given the highest priority. Coral reefs and mangroves are a first line of defence against storms, flooding, rising sea levels and other extreme weather events that can cause hundreds of millions or billions of dollars worth of damage and threaten people’s lives. As sea levels rise, it stands to reason that recognising the value of coral reefs and mangroves is essential to the protection of coastal communities.

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