Sea level rising, coast under threat

The sea level along Bangladesh's coast is rising at a rate higher than normal. This has been revealed in three different studies. The studies say that the rate at which the sea level is rising, there are apprehensions that further areas will be inundated or face excess salinity.

Around 8 to 15 per cent of land area of 4 coastal districts may go under water. Salinity in the coastal areas may see an abnormal rise too. This could have a harmful effect on the ecology, people's lives, agriculture, groundwater and infrastructure in the coastal regions.

These three studies were recently conducted by Bangladesh University of Engineering and Technology (BUET)'s Institute of Water and Flood Management (IWFM) and the government's Centre for Environmental and Geographic Information Services (CEGIS). The results of these studies were published on 8 May.

These studies were carried out at the initiative of the Bangladesh Department of Environment, with funds from the Climate Change Trust Fund project.

BUET carried out the study, 'Estimation of Sea Level Rise in Bangladesh Using Satellite Altimetry Data'. For the first time here the sea level rise was observed by means of satellite. The remaining two studies were carried out by CEGIS to determine the sea level rise and its possible future impact on water and agricultural infrastructure.

The Department of Environment's panel of experts accepted and approved of the three studies on the sea level rise and possible impact. This has been published under supervision of the Department of Environment.

Bangladesh is one of the countries at highest risk of global climate change. There is fear that the rise of the sea level may flood large areas along the coast. In the meantime, salinity along the coast is increasing.

The study revealed satellite pictures of the present state of sea level rise. Earlier the Department of Environment carried out research in context of the sea level rise over a span of 30 years.

Data for the study had been collected from the Water Development Board and the Bangladesh Inland Water Transport Authority's water measurements in 183 areas. But the tidal gauge data would be preserved manually, in writing.

There was a lack of clarity. In some cases the rise in sea level was seen to be abnormally high. In one instance, the rise in sea level along the Khulna coast was shown to be 6 to 21 mm.

The environment department's director (climate change and international convention), Mirza Shawkat Ali, said experts had reservations concerning the handwritten tidal station data. This data was not normal. Initiative was undertaken in the present studies to measure the sea level rise with the help of satellite readings. This is now a globally recognised method.

The research has endeavoured to determine the impact of the rising sea level on agriculture, water resources and infrastructure.

The IWFM report states that satellite altimetry can give a good solution to problems by measuring the water level from space. Using this method, the study has highlighted the picture of rise in the water level from 1993 to 2019 along the coastal floodplains of the Ganges, the floodplains of the Meghna estuary and the Chattogram coast.

The study reveals that in that span of time, the level along the Ganges coastal floodplains rose by 5.3 to 5.8mm every year. The level along the Meghna estuary floodplains rose by 4.2 to 5.3mm every year. And the rate of sea level rise along the Chattogram coast was 3.7 to 4.2mm every year.

Leader of the research team and IWFM's professor AKM Saifur Islam told Prothom Alo, the land along the coast is undergoing gradual subsidence. The rate of sea level rise in Bangladesh is much higher than the global average. For example, the sea level is rising annually by 12.3 to 12.8mm in the Ganges floodplains, 9.4 to 8.5mm in the floodplains of the Meghna estuary, and 7.7 to 9.2mm along the Chattogram coast.

According to the United Nations Intergovernmental Panel on Climate Change (IPCC), the global average rate of sea level rise from 1993 to 2020 was 3.42mm per year.

Professor AKM Saiful Islam is involved with IPCC. He said, "Our research showed that the average sea level rise in our country from 1993 till 2019 was 5.8mm. That means the sea level is rising here faster than the global average."

The IWFM report says, this rise in sea level is becoming unstoppable. This may cause harm to the coastal ecological system, increase salinity in the groundwater and damage infrastructure. This may lead to a serious food security crisis in the future.

For Shefali Bibi, 55, of Datinakhali village in Shyamnagar, Satkhira, clean drinking water is an everyday worry. The pond near her house was their main source of drinking water. After cyclone Aila struck in 2009, the tidal surge became saline. Now they have to fetch water every day from a pond around one and a half kilometres away.

It is not possible for Shefali Bibi or others of her six-member family to go every day to fetch water. However, a non-government organisation about a kilometre away, supplies drinking water. The family gets two large vessels of water every day from there for an annual fee of 500 taka.

A woman of Burigoalini union in Shyamnagar upazila is angry, "Are two vessels of water enough for the family in this heat? The sufferings that we undergo!"

Shefali Bibi's home is near the river Chuna. During the monsoons, at least this river had a flow of fresh water, but now there is salinity for a long span of time during the rainy season.

The people along the coast are seeing this change in nature up close. This is causing many of them to suffer.

The picture that has emerged from the three studies indicates that this suffering may increase in the future.

CEGIS has used three models of river current, the velocity of storms and salinity to highlight the possible impact of sea level rise.

The two studies indicate that if the sea level rises by 50cm (5.0mm X 100 years), 8 per cent of the coastal area will be flooded. If it rises by 62cm then 10 per cent, and by 95cm then 15 per cent, of the area will be inundated. The unprotected coastal areas of Gopalganj, Barishal, Pirojpur and Jhalkathi will see a higher amount of flooding.

The report also said that the sea level rise may lead to an increase in 1 to 5ppt salinity in 50 to 65 per cent of the areas along the coast. If the level of water goes up by 95cm, then the salinity in Barishal, Madaripur, Shariatpur, Gopalganj and Faridpur will increase by 1ppt.

CEGIS director (water management) Md Motaleb Hossain Sarkar told Prothom Alo, this increase in salinity will have an impact on agriculture. A rise in water level by 50 to 95cm can destroy 6 to 9 per cent of the aman rice crop. There may be a 1 to 5ppt increase in salinity in the floodplains of the Ganges estuary. The people of these areas may face an acute crisis of drinking water.

Bangladesh's Soil Research Development Institute (SRDI) routinely checks the state of soil in the country. According to the institutions latest report, in 2009 there was salinity in 93 upazilas of 18 districts in the country. In 2023 salinity increased in another three upazilas.

Chief Scientific Officer of SRDI's Khulna divisional office, GM Mustafizur Rahman, told Prothom Alo that the salinity along the coast is both increasing and spreading.

Speaking to Prothom Alo, hydrologist and professor at United International University, Mujibur Rahman, said, "With the rise in sea level and the shrinking of fresh water sources, salinity is increasing both on the ground surface and underground. We cannot control the rise in sea level. Global warming is responsible for this."

He said, "We can be more vocal at a global level regarding this matter. But as a country of the lower Gangetic plains, Bangladesh receives much less water than to which it is entitled. The flow of saline water could have been prevented if the flow of fresh water was normal. But that is not happening. In order to ensure equitable share of water, we need to strengthen regional cooperation with countries like India, China, Nepal and Bhutan."  

* The report, originally published in the print and online editions of Prothom Alo, has been rewritten for English edition by Ayesha Kabir