- A recent paper modeled how restoring mangroves in front of water-controlling infrastructure like dikes might create a hybrid coastal defense system in the face of global sea level rise.
- The model found that this combination, put in place today, could reduce the annual damage from storms and flooding by $800 million, and that 140,000 fewer people would be impacted by these events every year.
- They also found that these numbers would increase over time with the impacts of climate change.
- The researchers also evaluated where these projects would be most cost-effective, finding that the benefits disproportionately help lower-income areas, particularly in Southeast Asia, South Asia and West Africa.
With their dense mats of submerged roots, mangrove forests hold down shorelines worldwide like a coastal Swiss Army knife. They’re a nursery for juvenile fish and a home for important species in and out of the water. They’re also a filtration system for pollution, a holdfast against erosion, and a speed bump that slows incoming waves. But even the best of tools could occasionally use backup. A new study in the Proceedings of the National Academy of Sciences examines how combining mangrove restoration with water-directing dikes might multiply these ecosystems’ protective abilities even further, particularly as climate change worsens storm surges and raises sea levels.
As a hydrologist by training, Timothy Tiggeloven, lead author and environmental researcher at Vrije Universiteit Amsterdam, is particularly interested in how to manage unruly water by combining natural defenses (“green” infrastructure) with manmade creations (“gray” infrastructure) like dikes and levees. Though mangroves naturally reduce the height and power of waves, they don’t stop all of the water from a storm or flood from moving inland.
“So here comes this synergy of combination,” Tiggeloven said. “If you have a dike behind a mangrove, it will prevent the water from flowing over [onto land]. While if you only have dikes, they will be hit by the waves and there will be an overtopping. Having those two together is actually a very smart idea.”
So, Tiggeloven and his colleagues developed a computer model to assess where this combination would be most effective, and how the hybrid defenses might stand up under various climate change scenarios.
The model considered only those global mangrove forests that are currently degraded but could still be restored; for example, it didn’t include former mangrove forests that have been paved over, or healthy, untouched forest. The model assumed that all of these mangroves were already backed by dikes.
Their results suggest that under current-day conditions, this combination could reduce the amount of damage from floods and storms by $800 million every year. It also found that 140,000 fewer people would be affected by these events.
As climate change generates stronger storms and continues to raise global sea levels, the effect multiplies: with moderate greenhouse gas reductions and 2-3° Celsius (3.6-5.4° Fahrenheit) of warming, these numbers grow to an estimated $25 billion less in annual damage. Under the worst-case scenario, of little greenhouse gas reduction and more than 4°C (7.2°F) of warming, mangroves and dikes could prevent more than $65 billion in damage annually. In both scenarios, the model projected roughly 400,000 fewer people impacted every year.
Zooming in on specific regions, the potential becomes even greater. Under both present conditions and in a hotter future, South Asia, Southeast Asia and West Africa saw the greatest potential reduction in both damage and number of people impacted. The researchers also showed that funding restoration projects in these regions would cost less than the amount of damage storms could cause. Such projects would disproportionately benefit lower-income people, who already tend to be more exposed to coastal flooding.
“It’s very impressive,” Jonah Busch, an environmental economist who wasn’t affiliated with the study, said of the new paper. Though there’s growing interest among researchers in solutions that combine nature with manmade infrastructure, Busch said he was impressed with how the authors were “able to combine different types of models from across different disciplines — economic, engineering, biophysical — and bring them together in a way that makes sense.”
Experts say there’s a pressing need for these kinds of solutions. An estimated 147,000 square kilometers (56,800 square miles) of mangrove forest — an area nearly the size of Bangladesh — remain worldwide, down about 30-50% from their historical range over the last century. What’s more, a 2024 assessment of mangrove ecosystems by the IUCN, the global nature conservation authority, found that more than half of these surviving mangrove forests are at risk of collapse by 2050. Mangroves are largely declining due to human impacts like pollution, deforestation, dam construction and development, all of which render these ecosystems less resilient to rising sea levels and increasing storm severity.
Tiggeloven noted that the takeaway from his team’s research isn’t necessarily that people should begin building dikes behind all the world’s mangroves. Rather, he said, the findings could help highlight the places where mangrove restoration would be most effective, pointing to projects where mangroves have been deliberately planted in front of existing water drainage systems — as attempted along the coasts of Guyana and Suriname — or places where mangroves and dikes already exist but need water flow restored, like in the rice fields of Guinea-Bissau.
In future work, Tiggeloven said he hopes to use the same model as a foundation for testing other combinations of coastal defense, such as the interaction of dikes with salt marshes or coral reefs. And because of the broad framework of this model, it could also be used to more accurately assess the flood risk of coastal communities.
Busch echoed the same interest: “I would love to see similar analyses of this type and of this quality [examining how] does the restoration of upland watersheds lead to better water quality when combined with traditional management systems?” He said he’d also like to see future papers use this model to assess how gray-green infrastructure could potentially boost mangroves’ Swiss Army knife-like properties, as Busch has dubbed them, including carbon sequestration and fisheries benefits.
Modeling papers like this aren’t yet very common, though. Busch said one reason is that research into combining gray and green infrastructure is a relatively new field of study. Another is that the models needed are spread across different disciplines, which often don’t talk to each other.
And bringing these ideas to life as actual infrastructure projects is yet another hurdle.
“Besides the science of it, doing these things in real life involves bringing people together from different backgrounds and industries,” Busch said. “So, building a dike is engineers, restoring mangroves is ecologists. Land-based restoration projects are challenging enough. Infrastructure projects are challenging too. Then trying to do both together, in the water, is even more so.”
However, research like this, he added, is exactly what experts need to get this kind of work started. “This paper really should put wind in the sails of green-gray infrastructure and ecosystem-based adaptation,” Busch said.
Living in Amsterdam, dikes are a common sight for Tiggeloven; mangroves, less so. But on recent trips to Brazil and southern Japan, he had the opportunity to spend some time in the very sort of mangrove forests he’s been modeling on computers.
“It changes how I see this work a lot,” he said. “To see it in real life, see how communities are living near them, see the fisheries next to the mangroves — it tells a story. It already gives this research some added value for myself.”
Banner image: Key deer (Odocoileus virginianus clavium), a tiny and endangered subspecies of white-tailed deer, walk along mangroves in Big Pine Key, Florida. Image courtes of AP Photo/Lynne Sladky.
One-two punch for mangroves as seas rise and cyclones intensify
Citations:
Tiggeloven, T., van Zelst V., Mortensen, E., van Wesenbeeck, B. K. Worthington, T. A., Spalding, M., … Ward, P. J. (2026). Mangrove restoration and coastal flood adaptation: A global perspective on the potential for hybrid coastal defenses. Proceedings of the National Academies of Science, 123(4). doi:10.1073/pnas.2510980123
Winterwerp, J. C., Bayney, A., Engel, S., Jack, L., Moseley, K., & Smits, B. (2025). Mangrove recovery by habitat restoration using nature-based solutions. Ecological Engineering, 212, 107520. doi:10.1016/j.ecoleng.2025.107520
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