Satellites are helping Wetlands International to protect and restore mangroves.

After the 2004 Indian Ocean tsunami, the non-profit organisation discovered that many lives had been spared in area which had been protected by mangroves. Wetlands International gained a little help from space in scaling up its work protecting and restoring these vital habitats and complex ecosystems with images from the European Space Agency’s Copernicus Sentinel-1 and -2 satellites. The Sentinel missions carry a range of technologies, such as radar and multi-spectral imaging instruments for land, ocean and atmospheric monitoring.

Mangroves make up just a small proportion of the world’s forest but are home to fish, shellfish, birds and mammals. They store more carbon per hectare than rainforests and protect coastal communities from extreme weather. Wetlands International discovered they were able to reduce the destructive force of a tsunami by up to 90 per cent.

Lammert Hilarides, an information manager at Wetlands International explained: “After the 2004 tsunami we saw that areas with intact mangroves suffered far fewer deaths and less damage than those with lost or damaged mangroves.”

Between 1996 and 2016, around 6.6 per cent of mangroves were lost worldwide. This was down from 1 per cent per year in the 1980s.

Mangroves under pressure from climate change

“Historically, the biggest risk that mangroves face is from conversion to agriculture on the land side, and to aquaculture on the sea side,” said Hilarides. “But there is also growing pressure from climate change, with rising sea levels starting to overwhelm mangroves and changing rainfall patterns causing some to die off because of a lack of fresh water.”

An online platform called Global Mangrove Watch is providing remote sensing data and tools for coastal and park managers, conservationists, policymakers and practitioners to respond by pinpointing the causes of local mangrove loss and tracking restoration progress.

Together with Aberystwyth University and soloEO, Wetlands International is a key partner in Global Mangrove Watch. Hilarides explained how the platform works: “We use satellite data to produce a map of all the mangroves around the world once a year. It currently goes to 2016 but later this year we will release maps up to 2020.”

“Change alerts” help detect destruction

The platform enables park managers, conservationists and policymakers to detect destruction and stop it in time. The information is passed on immediately through alerts.

“We also use data from the Sentinel-1 and -2 and Landsat 8 satellites to provide what we call ‘change alerts’ for Africa.” said Hilarides. “The Sentinels reimage the same location every few days, so once a month we compare their new images with a baseline map. We send out alerts if we see a difference in mangrove cover.”

The current baseline map was built using 2010 data from the US Landsat and Japanese ALOS satellites and the team is updating it using 2021 data from the Copernicus Sentinels. Higher resolution data from the satellites will give the new map a resolution of just 10 metres, compared to the current 25 metres resolution.

Change alerts have already been used to catalyse action: “Our change alerts currently cover Africa, but we will soon be providing them for five of the most mangrove-rich countries, including Mexico and Indonesia. We hope that the alerts will be available for the whole world in the next couple of years.”

Hilarides added: “I want to emphasise how happy we are with the Sentinel images. They are free, high resolution, and available almost immediately after they are taken. This means that we can act quickly to protect and recover mangroves worldwide.”

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