Coping with storm surges in the Sundarbans

Villages located near rivers, creeks and low-lying areas of the Sundarbans – the world’s largest mangrove forest that straddles Bangladesh and India – are more vulnerable to storm surges than villages further inland, according to a new study by scientists from New Delhi’s Jamia Milia Islamia University. The frequency of storms is projected to increase due to global warming,

The scientists assessed people’s vulnerability as a function of exposure, sensitivity and resilience capacity, and developed a composite vulnerability index (CVI) based on the three factors. They found that villages located in the lower and southern parts of the Sundarbans were the most vulnerable to storm surges. Most of these villages are near rivers and creeks, while others are located in low-lying areas. Conversely, villages located at higher places faced fewer storm surges.

But some villages in the northern part of the Sundarbans – further from the Bay of Bengal – are also highly vulnerable due to presence of low-lying and waterlogged wetlands, the study found.

The findings of the study, reported in Remote Sensing Applications: Society and Environment Journal, may have implications for developing resilience capacity in response to storm surge flooding, the scientists say. The authorities can now prioritise the more vulnerable villages when they provide information on what residents should do when a storm threatens.

Identifying vulnerable villages

The study has identified vulnerable villages, and “nascent efforts will now be made to assess vulnerable populations” within these villages, says Haroon Sajjad, lead author of the study. “Poor coastal zone management, limited livelihood facilities, low level of infrastructural development and insufficient institutional management have all made the Sundarbans coast more vulnerable to climate-induced disasters.”

“It is hoped that the government will take necessary steps,” Sajjad adds. These include designing local measures to reduce poverty, exploring tourism as an alternative source of income, developing community infrastructure such as cyclone and flood shelters, and improving early warning systems.

While the recommendations are unexceptionable, parts of the study are not. Tuhin Ghosh, assistant professor at the department of oceanographic studies at Jadavpur University in Kolkata, who has worked extensively in the Sundarbans, disagrees with some of the findings.

Ghosh says that the maximum surge height of 15.6 metres over a 120-year period as reported in the new study “is a gross overestimation, and more than twice than the storm surge height during the super cyclone in Odisha in 1999.”

Ghosh cites a previous study published in the Environmental Fluid Mechanics journal, which showed that the estimated peak storm surge in the Sundarbans was about four metres.

He argues that the funnelling effect of the Bay of Bengal and the intricate network of rivers and tidal creeks in the Sundarbans delta dissipates a storm surge to a large extent. “The proximity of the coastline must be considered as a reduction factor, and an important variable in the vulnerability analysis,” Ghosh says.

Bangladesh and India share the Sundarbans, an area of about 25,500 sq. km. Of this, roughly one-third lies in India. The Indian part of the Sundarbans is bound by water on three sides — the Hooghly River to the west, the Ichamati-Raimangal River to the east and the Bay of Bengal to the south. Half of its 102 islands are inhabited.

Most of the people live below the poverty line — earning less than USD 1.5 a day. With limited access to resources they are often unable to cope with storms and floods.

Salty waters

As storm surges are expected to increase in the Bay of Bengal due to climate change, the floods that they bring in their wake “will have far reaching socio-economic and ecological implications,” the report by Sajjad cautions.

With the incursion of more seawater due to storm surges, croplands and settlements will become more saline, making agriculture more unproductive. Meanwhile, the mixing of seawater with swamps in the area will also “have deleterious impact on the biodiversity of the region,” the study says.

See: Saline land will drive people out of Sundarbans

Scientists and policy analysts are already reporting some long-term impacts of storm surges in the Sundarbans, which has undergone major economic and social changes over the last 15 years and witnessed the displacement of an estimated 70,000 people.

For example, agriculture was heavily affected after the 2009 cyclone Aila that devastated the Sundarbans. Some of the farmland inundated by seawater is till lying fallow, nearly ten years later. Production of freshwater fish has declined significantly.

Sajjad’s findings are in line with a 2017 report of the World Bank, which says that the southwest coastal region of Bangladesh – which is also largely covered by the Sundarbans – is already becoming increasingly saline, especially between October and May, when the area receives almost no rainfall . Laboratory analyses of water and soil samples show an increase in salinity over time in the region. “Climate change induced sea-level rise will further intensify the problem of river and soil salinisation,” the report says.

The World Bank predicts that the progressive salinisation of water and soil will significantly impact the fragile ecosystem of the Sundarbans, a UNESCO World Heritage Site, and affect the people living in and around the forest.

The Bank says, “Increased water salinity will alter the aquatic ecosystem and the mangrove forest, along with significant shortages of water for drinking and irrigation in the south-west coastal area (of Bangladesh), while soil salinisation is likely to lead to a significant decline in the output of high-yielding rice.”

Contentious embankments

Some scientists and policy analysts also say that the government’s eagerness to build embankments as the main way to protect the residents of the Sundarbans  from flooding ends up compounding the problem.

John Pethik, a retired professor and coastal science expert at Newcastle University, Britain, who has worked extensively on the Sundarbans coast, says that his research shows “the construction of flood defences in the Sundarbans has acted to increase the rate of sea level rise and thus the vulnerability of its inhabitants. Such constructions amplify the tidal wave as it passes into the channels constricted by embankments.”

The Sundarbans is a delta built by silt, brought down by the rivers in the Ganga-Brahmaputra-Meghna basin. It is known that the entire Sundarbans region is subsiding, because the silt is increasingly stuck behind dams and barrages upstream. Pethik’s studies have also shown that while deltaic subsidence amplifies the effect of sea level rise in the Sundarbans, the main culprit is the increased tidal waves in the channels constricted by embankments.

Still, all is not lost. A February 2018 paper from the  Social, Technological and Environmental Pathways to Sustainability (STEPS) Centre at Sussex University says that despite the predominantly top-down policies that “hamper efforts to support locally appropriate and socially just adaptation” in the Sundarbans, there are some signs of hope for emerging alternate ways forward.

Agricultural scientists, non-government organisations and local people are experimenting with ways to revive traditional paddy crops that can survive the increasingly salty conditions. This could usher in changes in agricultural practices, which can help farmers, and build more resilient crop systems.

See: Organic farming gathers steam in the Sundarbans

There are similar experiments on raising fish and prawn species that can tolerate more saline water. “While these alternative pathways can help build local resilience, it is important that they are accessible and affordable to the poorest of the poor, especially in a region where most of the people are below the poverty line,” the new study says.

This article was originally published in indiaclimatedialogue.net.

See: Reporting common issues in transboundary Sundarbans
See: Indigenous peoples in Sundarbans ruined by lockdown, cyclone.
See: Community-run tourism can help Sundarbans cyclone recovery