India: Sundarbans vulnerable to storm surges

Villages located near river creeks and low-lying areas of the Sundarbans are more vulnerable to storm surges, whose frequency is projected to increase due to global warming, a study by scientists from Jamia Milia University in New Delhi says.

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.

Villages located in the lower and southern parts of the study area were found to be 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 study area were highly vulnerable due to presence of low-lying and waterlogged wetlands.

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. It can help the local policymakers integrate local multi-hazards knowledge and provide information in a form that can help take action to both mitigate and adapt to storm surge floods, they say.

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 Sundarbans coast more vulnerable to climate-induced disasters,” he said.

“It is hoped that the government would take necessary steps towards policy recommendations,” Sajjad added. These include location-specific poverty reduction measures to reduce overall vulnerability; exploring tourism as an alternative source of income; community infrastructural development; and improved early warning systems and cyclone and flood centres that serve as shelters during extreme events.

However, Tuhin Ghosh, assistant professor at the department of oceanographic studies at Jadavpur University in Kolkata, who has worked extensively on the Sundarbans and analysed the impacts of the storm surge due to the 2009 cyclone Aila on more than 3,500 km of the old earthen embankments, disagrees with some of research findings.

Ghosh says that the maximum surge height, over a 120-year period of 15.6 m in the study area, 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 Environmental Fluid Mechanics journal, which shows that the estimated peak storm surge was about 4 m in the Sundarbans region that propagated into all major rivers, inundating the riverbanks as well inland areas.

Ghosh cites this report to point out that the funnelling effect of the Bay of Bengal and intricate network of rivers and tidal creeks in the Sundarbans delta construct a more complex system that may dissipate the propagation of 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,” he says.

Bangladesh and India share the Sundarbans, an area of about 25,500 sq. km that is home to the world’s largest mangrove forest. Of this, roughly one-third — nearly 9,630 sq. km — lies in India. In India, the Sundarbans is bound by water on three sides — Hooghly River to the west, Ichamati-Raimangal River to the east and the Bay of Bengal to the south. Only 54 of its 102 islands are inhabited.

Most of the people are below the poverty line — earning less than USD 1.5 a day — with limited access to resources, and are, hence, unable to cope.

Salty waters

As storm surges are expected to increase in the Bay of Bengal due to climate change, the flood inundation that they bring in their wake “will have far reaching socio-economic and ecological implications on the study area,” 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,” it says.

Scientists and policy analysts are already reporting some long-term impacts of storm surges in the study area that has undergone major economic and social changes during 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 deltaic area, with most of the agricultural land lying fallow till date. Similarly, fish production has declined significantly.

Sajjad’s research findings are in line with a 2017 report of the World Bank, which says that the southwest coastal region of Bangladesh is already becoming increasingly saline, especially between October and May. Laboratory analyses of water and soil samples show an increase of 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.

World Bank studies also predict that the progressive salinisation of water and soil in a changing climate 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 report 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, 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 tendency of governments to build embankments to protect the Sundarbans residents from flooding end up compounding the problem due to sea level rise and tidal waves.

John Pethik, retired professor and coastal science expert at Newcastle University, Britain, who has worked extensively on the Sundarbans coast, says that his research “has demonstrated that 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.”

Pethik’s studies have also shown that while deltaic subsidence, amplify the effect of sea level rise in the Sundarbans, the main culprit is the increased tidal waves in the channels constricted by embankments.

Yet there are signs of hope. A February 2018 paper of Social, Technological and Environmental Pathways to Sustainability (STEPS) Centre says that despite the predominantly top-down, out-of-context policies that “can often hamper efforts to support locally appropriate and socially just adaptation” in the Sundarbans, there are some signs of hope for emerging alternate pathways.

Experiments are on by agricultural scientists, non-government organisations and local people to revive salinity-resistant traditional paddy crops, which could usher in changes in agricultural practices, which can help farmers, build climate-resilient crop systems.

There are similar experiments on culturing fish and prawn species that can tolerate salinity. “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 working paper says.