Mangroves: We Used Freely-Available Satellite Images To Track Climate-Resilient Forests

(MENAFN- The Conversation) Mangroves are one of most important ecosystems on the world's coasts. They absorb the impact of storms, prevent erosion, provide food and safety for fish and other animals and can store huge amounts of carbon in the mud that builds up below them.

However, due to their delicate location in the transition zone between the land and the sea, they also face several human-made threats such as pollution and climate change-driven sea level rise.

That's why it is critical to get updated and accurate information on the whereabouts and extent of mangrove forests in order to conserve and manage them more effectively. In our latest research , we used images captured by Earth orbiting satellites to map the past and present mangrove cover on the tropical island of Mauritius.

Islands are particularly vulnerable to climate change, especially its effects related to the sea, such as a rise in sea level or increasingly powerful hurricanes. Like many other small islands, Mauritius relies heavily on its coast as a source of income. That's why it's crucial to be able to take quick action to protect itself and handle the impacts of climate change.

Mangroves have long been recognised as a natural way to mitigate such threats. We used freely available satellite images to track them in Mauritius, which could eventually help support the island's efforts to adapt to a changing climate.

We collected GPS coordinates of mangroves at two sites, Le Morne in the south and Ferney in the south east. Le Morne is a fairly new mangrove plantation site within sandy beaches. Mangroves at Ferney have grown naturally, are mature and grow mainly along the muddy banks of the Champagne River.

We then retrieved free satellite images from the Earth orbiting satellites SPOT-5 for the year 2013 and Sentinel 2A for 2023. We analysed the data with user-friendly software that did not require programming skills. We trained and tested our model using the field data we collected and obtained results with accuracy of 90% and above compared to data gathered on the ground.

With the satellite images, we found that mangrove cover increased significantly at Le Morne from 0.06 hectares (ha) in 2013 to 4.6 ha in 2023. This was as expected: it's an active mangrove plantation and has been for years. Our results are in line with the actual extent of mangroves as measured by people on site.

At Ferney, we also noted an increase of from 20.8 ha in 2013 to 26.3 ha in 2023. Here, we attribute the increase to natural regeneration taking place in adjacent mudflats.

The technique we used in this study shows that satellite images and graphical software can do an efficient job mapping mangroves across landscapes. This can provide useful insights to support decision making to increase resilience to climate change.

Generally, ecosystem monitoring using satellite imagery is still in its infancy in island nations like Mauritius. This is due to several challenges especially the lack of human expertise and programming skills among biologists.

But if we can address these issues, we can use satellite images to obtain critical information. For instance, satellites can detect changes – such as the forest growing, shrinking or thinning – earlier than might be apparent from the ground. Satellites equipped with radar or specialised sensors can measure the height and structure of forests, which can provide valuable information on biomass density and hence how much carbon the forest has the capacity to store.

Satellite images can also help engage local people in restoration efforts and they can help scientists map changes along the coast and assess how vulnerable mangroves might be.

When we monitor mangroves using such techniques, we can become more resilient to climate change. Overall, our study shows how technology like satellite imagery analysis can provide precise, repeatable and cost-effective monitoring of mangroves.

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