Damage from Cyclones in the Sunderbans

Damage from Cyclones in the Sunderbans

• Scientists used satellite images to capture changes in the Sundarbans mangroves, following cyclones.
• Mangroves are known to be resilient to the impact of cyclones to protect the shoreline from getting eroded. But that was true when so much pressure from human activities wasn’t there.
• The data was collected from optical (Copernicus Sentinel-2 satellite mission), radar (Copernicus Sentinel-1 satellite mission), and LiDAR (Global Ecosystem Dynamics Investigation) platforms.
• Frequent cyclone damage slows the recovery of mangroves and changes the forest composition in comparison to other regions that didn’t witness many cyclones.
• Of the three recent cyclones (Bulbul, Fani and Amphan), cyclone Amphan caused the most damage to the Sundarbans mangroves with the highest mangrove loss along shorelines that were eroding over the past 35 years.
• The Sundarbans mangrove ecosystem in India is classified as endangered in the IUCN’s Red List of Ecosystems framework.
• Historical threats came from clearing mangroves dating back to the 1800s and declining fish populations.
• Ongoing threats like climate change and reduced freshwater supply are heaping pressure on this ecosystem.

Why mangroves are important?

• Mangroves are incredibly productive coastal ecosystems found in the tropics and subtropics. These dense green forests are known for their bizarre-looking roots that poke up into the air from shallow water. Among the meshed webs of roots are fish nurseries, enabling humans to make a living from the marine life in and around the mangroves.
• Mangroves also play another important role for humans, protecting communities from major storms. Climate change is more than rising temperatures, and the increased frequency and intensity of cyclones, hurricanes and typhoons is apparent.
• Mangrove roots can break up the force of a storm surge, soaking up some of its energy and protecting people living on coasts from cyclone damage. Yet it is a challenge to effectively value and protect individual mangrove ecosystems. And we just don’t have the people or funds to deliver detailed studies for even a fraction of the villages and towns sheltered by mangroves.
• Mangrove forests cover just 0.5% of the world’s coasts but account for an estimated 10-15% of coastal carbon capture. As we try to stop CO₂ levels rising and put the brakes on climate change, protecting mangroves for their blue carbonvalue is key.
• Mangrove protection from cyclones also reduces longer term deterioration of low-lying inland areas with rising sea levels. Storm surges and flooding from cyclones, which deposit salts, are greater without mangrove protection. In Bangladesh, for example, rice agriculture is increasingly impossible as fields are flooded with seawater.
• One way communities are adapting is to shift production to shrimp farms. Booming shrimp aquaculture, however, ironically requires further mangrove clearance to create space – as seen graphically in Sri Lanka. Loss of mangrove protection from cyclones then worsens coastal deterioration.

Statistics

• Data analysis showed that as much as 73.5 percent of the entire Sundarban mangroves witnessed a decline in the NDVI (normalized difference vegetation index) values (plant health) after Amphan – likely due to annual variability and not cyclone-related damage.
• However, about 3.45 sq. km. of the Sundarban mangrove forest (roughly 0.05 percent) had a considerably lower NDVI value almost a year after Amphan, which likely reflects the damage from the cyclone.
• Shorter mangrove stands were more widely affected, whereas the range of extreme damage decreased for taller mangrove trees.
• This difference in mangrove damage is likely because Amphan’s eye and track were closer to the western Sundarbans with shorter trees than the eastern side with relatively taller trees.
• the southern and western regions of the Sundarbans in India and Bangladesh showed the most damage to the mangrove cover following the cyclone.
• These most affected regions translate into the eastern part of Indian Sundarbans.