How mangroves in Odisha, India likely reduced Cyclone Dana’s impact 

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Cyclone Dana, which made landfall close to Bhitarkanika National Park and Dhamra Port in Odisha at 3.30 am on Friday, did not cause significant damage as many had feared. Although efforts by state authorities helped limit the devastation — for instance, Odisha evacuated one million people to cyclone shelters — there was one non-human factor that also played a crucial role. It was the rich mangrove forest cover of Bhitarkanika.

What are mangroves?

Mangroves are salt-tolerant trees and shrubs typical of estuarine and intertidal regions, meaning they grow in areas where freshwater and saltwater meet. Mangroves typically have aerial, breathing roots and waxy, succulent leaves, and are flowering plants. The Sundarbans (spread across India and Bangladesh) is the largest contiguous mangrove forest in the world. Mangrove seedlings called propagules germinate on the parent tree before falling into the waters and growing into a mangrove tree again.

Red mangrove, Avicennia marina, grey mangrove, rhizophora etc. are some common mangrove trees. Abundant in swampy and marshy areas, mangroves represent a littoral forest ecosystem, which means they thrive in saline or brackish waters in coastal regions.

In India, many locations boast of mangroves. The Godavari Krishna delta in Andhra Pradesh, Bhitarkanika in Odisha, mangrove forests in Andamans, Kerala, Gujarat, Tamil Nadu, etc., are some examples.

How do mangroves protect against cyclones?

When cyclones strike, mangrove forests act as a barrier against storm surges — a change in sea level caused by a storm, usually leading to large waves — by obstructing the water flow with their roots, husks, and leaves, according to a report published by the World Bank Group.

A different report by the group revealed that some of the mangrove species such as Sonneratia apetala “reduced the surge height from 4 cm to 16.5 cm with 50 m to 2 km wide mangrove strips, and reduced the water flow velocity from 29% to 92% with 50 m or 100 m wide mangrove forests”.

When mangroves are combined with built infrastructure, the impact of a cyclone can further be reduced. For instance, planting mangroves in front of an embankment can decrease water flow velocity, the report said.

What vast is Bhitarkanika’s mangrove forest cover?

Currently, Odisha has a reserve of a mangrove forest area of 231 square kilometres with a major chunk lying in Bhitarkanika. It stands second only to Sundarbans in West Bengal. Besides Bhitarkanika in Kendrapara, the districts of Balasore, Bhadrak, Jagatsinghpur and Puri are also home to mangroves, otherwise known as coastal woodland.

While 82 sq km area in Bhitarkanika is densely mangrove-infested, 95 sq km area has moderate mangrove forest. The coastal patches spread across 672 sq km were declared the Bhitarkanika Wildlife Sanctuary in 1975. The core area of the sanctuary, with an area of 145 km, got the National Park tag in September 1998.

The park has withstood the onslaught of several cyclones in the past including the Super Cyclone, which took place in October 1999.

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