BHUBANESWAR: Cyclonic storm Amphan had a severe eco-physical impact on the coastlines of Odisha, West Bengal and Bangladesh, eroding shorelines and damaging mangrove vegetation.
This was revealed by a technology-backed study on the impact of cyclones along the eastern coast carried out by a group of four independent researchers of Khallikote University and Sambalpur University in Odisha, Adamas University in Kolkata and Delhi University.
They observed the highest seashore erosion of 186.47 metres was in Balasore, 275.53 metres in Patharpratima Island in West Bengal and 486.85 metres along Patharghata region of Barisal subdivision in Bangladesh.
Although impact on humans and economy is assessed by the government post cyclone, ecology is often ignored. The analysis of the shoreline change in Odisha showed erosion in 43.93% of the transects while it was highest at 76.94% in Bangladesh and 64.94% in West Bengal.
The entire coastal region of 48,212.4 sq km was affected by the Amphan cyclone that hit the coast between May 16 and 20 last year. Researchers found a total of 4,545 transects post-cyclone in the study region.
The study conducted using geospatial technology revealed erosion in 60.33% of the total transects of the coastline analysed and growth in only 24.99% of the transects. Around 14.68% of the total transects depicted stability.
Odisha's coastal districts -- Kendrapara, Bhadrak and Balasore -- where 40.93% of the total transects are erosional in nature were affected in the cyclone.
"The maximum erosion of 186.47 metres was seen in the northern part of the spit near the northeast extent of Balasore district. Incidentally, the highest accretion of 137.85 metres was also observed along the southern part of the spit," said researcher Manoranjan Mishra.
However, the shoreline of West Bengal districts (East Medinipur and South 24 Pargana) had 64.94% of its total transects under erosion while 19.86% of the total transects showed a trend of accretion and 15.2% of the total transects depicted stability.
The highest erosion was observed on the eastern extent of the Patharpratima Island, near the landfall location of Bakkhali in West Bengal. The highest accretion of 125.47 metres was found in the northern bank of the mouth of Pichaboni river in WB.
The eastern coastal region is the locus of cyclone landfalls that occurred during the past 140 years. The most critical tropical ecosystem -- Sundarbans mangrove area and Bhitarkanika mangrove and Biosphere Reserve -- fall in the region.
The decreasing trend in vegetation over the South West coastal region of Bangladesh and reducing mangrove vegetation will critically affect these ecologically fragile regions and expose the landform and the communities to the direct impact of cyclones in the post-Amphan period. It will also have
repercussions on the coastal communities.
Associate Professor at the Department of Natural Resources Management and Geo-Informatics, Khallikote University, Mishra said Amphan had also significantly impacted vegetation and the green cover degraded along the Bangladesh coast. The relatively lesser impact of the cyclone on the Odisha coast possibly kept the vegetation greenness healthier.
"The shoreline of West Bengal had the average landward movement of 14.51 metres and in Bangladesh, the shoreline migrated landward with an average distance of 32.34 metres. The loss of vegetation also gives rise to man-animal conflicts in the study region," he maintained.
Ortho-rectified Landsat imagery from April to July in 2020 signifying the period before and after the cyclone was used to ascertain the shoreline change. The monitoring of vegetation was conducted using images derived from NASA's Moderate Resolution Imaging Spectroradiometer (MODIS).
Other members of the study group included Dipika Kar of Department of Natural Resources Management and Geo-Informatics, Khallikote University, Manasi Debnath of Department of Geography, School of Basic and Applied Sciences (SOBAS), Adamas University, Netrananda Sahu of Department of Geography, Delhi School of Economics, Delhi University and Shreerup Goswami of Department of Earth Sciences, Sambalpur University.