Nature-based solutions are still misunderstood

You can’t attend a conference on combatting the effects of climate change without hearing the term ‘nature-based solutions.’  It’s hardly surprising. The notion of co-opting nature, such as supporting mangrove forests to prevent coastal erosion, is a no-brainer. Yet why are most planners, engineers, and financiers slow to embrace these and other nature-based solutions? What are the obstacles? Can they be overcome and how?

A mangrove forest is a marvel of natural engineering, and given the right circumstances, its wave-dampening properties will reduce the height and, therefore, the capital required for traditional sea defences. The forest’s dense biomass and tight root systems are remarkably resilient against wave action, even cyclones, and can thrive in harsh coastal environments with little oxygen in the soil. As sediments settle around tree roots, they contribute to the gradual build-up of land, staying one step ahead of the rising sea levels and waves. Mangroves are also an effective carbon sink, extracting four times as much carbon from the atmosphere as a tropical rainforest, locking it safely away. 

So why aren’t planners turning immediately to nature-based solutions (NbS) rather than relying solely on ever-higher concrete sea walls?

Firstly, NbS are the outcome of a holistic approach where the natural system is our starting point. NbS evolve from that natural state and are both nourished by and support their environment. Take a mangrove forest, it’s not a building block or stand-alone solution like a sea wall, but a living system that’s dependent on abiotic factors such as river flow and sediment and connected with other biotic factors such as coral reefs, fish, and other species. For example, in most cases, you should not plant a thin strip of mangroves before a sea wall, as it is likely to be eroded from behind by wave energy reflected from the wall. To function well, mangroves in a coastal protection scheme should have the ability to ‘move’ as they are part of a dynamic system. Also, to survive and grow with sea-level rise, the trees will require a continuous water flow that delivers sediment, nutrients, and fresh water. 

The second impediment concerns governmental regulations on coastal protection, for example specifying the requirement of an offshore breakwater in Vietnam. These vary by country and by region. Overturning these rules can be challenging, even when breakwaters interrupt the natural sediment supply from the sea to the coastline. 

We have also seen the request for mangroves within a project, only to discover what the client really wanted was a concrete sea dike with a park, or guidelines on how to build walls within the mangrove forest. The mangroves merely ticked the proverbial green box and played no significant role in the coastal protection scheme.

Thirdly, the availability of land remains an issue, particularly where areas suitable for planting mangroves are close to a city or agricultural areas. Mangroves can grow naturally, but land must be turned over for this, either seaward or landward. Seaward can be difficult if the water depth is too deep for mangroves to grow. When it’s landward, councils, farmers, and local landowners are often hesitant to surrender their land, especially when it’s an important source of income. This means that financial compensation schemes are required.

Understanding the ROI of NbS

Consequently, the biggest obstacle preventing mangroves from flourishing beyond pilot projects is financing, despite that many projects would pay for themselves when you calculate their overall economic impact. After all, mangroves dampen waves, which means that the sea dike can be lower or will last longer. Lower sea dikes mean less use of materials and less construction costs. From that alone, the project can already be financially feasible.

The impact on local communities can be profound. Jobs are created in seed collection, planting, and maintaining the forests, and maintenance is ongoing just as it would be for a dike or sea wall – a cost often neglected. Fishermen also benefit. In a project in Pakistan, locals reported a threefold increase in their fishing and crab catches. In a project in the Mekong, involving the restoration of wetlands and a flooded forest, a modest 1% increase in the fish catch would be enough to justify the entire cost of the restoration project.

Like most NbS, mangrove projects rarely fit accepted ROI models, and those making the investment are not necessarily the people who benefit most. Furthermore, even when it leads to substantial cost savings, such as dispensing with the need to heighten sea walls, cautious engineers often fail to place their faith in the natural solution.

Overcoming the barriers to nature-based solutions

We must first appreciate that mangroves and other NbS are different. They are living systems. Implementing them necessitates an understanding of the biotic and abiotic systems and how they work with each other. Partnering with an NbS expert with experience in mangroves and local conditions is obvious but vital.

Another priority is ensuring stakeholders factor in the social value of the NbS as an additional economic benefit. The precise calculation and how to communicate it need to be simple for investors and communities to determine the actual ROI. 

Finally, we need better blueprints or design guidelines for implementation. Engineers require them to be as prescriptive as possible – not an inspirational catalogue but detailed how-to guidelines. Such as what kind of mangrove trees? At what height? What sort of flow, sediment, and bed depth? Formulae to correlate the size and age of the mangrove strip with its wave-dampening efficacy, and how that translates to a percentage reduction in the height of a sea wall or a decrease in the buffer level. Then, how does that translate into dollar or euro savings? The guidelines are needed for the whole project cycle, encompassing design, implementation, monitoring, and maintenance, including guidance on economic opportunities and stakeholder processes.

Offering firm guidelines for banks and engineers to incorporate into their standards is the way forward. The same specificity should apply to other NbS, from developing salt marshes to oyster beds. 

Nature is a powerful ally. However, we need to increase our understanding of natural engineering and articulate the social and financial benefits. Only then will mangroves and other NbS turn from pilot projects into full-scale coastal defence strategies.

This article was originally published in The Manila Times on June 15