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Natural coastal land expansion offers hope to low-lying Bangladesh

Date published
03 May 2021
Description

 

Kabir Uddin, Kundan Shrestha, and Rajesh Bahadur Thapa

Coastal land expansion in northern Bay of Bengal (1989–2018): Dark green represents regained land area that is unchanged, light green shows gradual reformation into a new island area, and pink represents land area lost into waterbodies. The net gain in land for Bangladesh during this period was around 1.15% (590 km<sup>2</sup>).

Coastal land expansion in northern Bay of Bengal (1989–2018): Dark green represents regained land area that is unchanged, light green shows gradual reformation into a new island area, and pink represents land area lost into waterbodies. The net gain in land for Bangladesh during this period was around 1.15% (590 km2).(Image: Uddin et al., 2020)

Bangladesh is one of the most densely populated countries in the world – almost three times as dense as India. Naturally, land is an invaluable, limited resource and a productive asset which provides not only habitat but also sustenance and livelihoods. Alarmingly, with rising temperatures, around 40% of productive land in the southern coastal region of the low-lying country is likely to be submerged by 2080. This would mean that rich coastal biodiversity would be engulfed by the Bay of Bengal, and entire communities – and their homes, livelihoods, and way of life – would be displaced, putting further pressure on the country’s limited land and resources. However, a serendipitous natural phenomenon could offer some respite for Bangladesh’s coastal population and environment: gradual land expansion over decades in the coastal regions.

How are these new land areas forming?

This land expansion throughout Bangladesh’s coast is caused mostly by natural processes. Major rivers from the Himalaya such as the Brahmaputra, Meghna, and Padma carry around one billion tons of sediment and deposit it across northern Bay of Bengal through Bangladesh. These sediments accumulate in the estuaries of Meghna River, causing significant changes in the bay’s morphology and giving birth to new lands. Human activities such as the diversion of river water, extraction of sand, and infrastructure development could exacerbate these processes of deposition.

We studied this interesting development – just another example of the complex interaction between mountains and oceans – using multi-temporal satellite data over a 30-year period (1989–2018) and found that the coastal region is gaining significant land area through newly formed islands (called “char” locally) and the extension of the main land mass. Land expanded every year by an average of 20 km2 along the coast, totaling 592 km2 of new land in the three decades. To put this into context, this is almost double the size of the Maldives – another low-lying South Asian country.

Study area: (a) a river that originates in the mountains drains into the northern Bay of Bengal, forming the largest riverine delta in the world; (b) study area comprised the Meghna estuary and Northern Bay of Bengal, represented by Landsat natural-colour images.

Study area: (a) a river that originates in the mountains drains into the northern Bay of Bengal, forming the largest riverine delta in the world; (b) study area comprised the Meghna estuary and Northern Bay of Bengal, represented by Landsat natural-colour images. (Image: Uddin et al., 2020)

From muddy barren lands to grasslands

Most of the offshore islands have formed in the estuary of the Meghna River. Among the quickly formed islands, Bhashan Char, Char Nizam, Jahajerchar, and Urir Char are prominent. When these islands were newly formed, they were muddy and barren. A field mission (under the Bangladesh National Geographical Association and led by Professors M. I. Chowdhury and Bir Protik M Shamsul Alam) in January 1977 to the newly formed Nijhum Island in Hatia reported sparse grass cover and no settlement. Considering salinity issues, groundwater was the only source of drinking water.

Today, a combination of coastal greenbelt initiatives by the Ministry of Environment, Forest and Climate Change and other agencies, along with natural vegetation growth, has transformed some of these islands into grasslands with closed tree canopy cover. These efforts have prevented these new islands from being submerged in tidal waters or tropical storms. This has led to more settlements in islands. These newly formed islands are not suitable for agriculture in the early years of formation, but soil fertility can increase because of the silt transported by Himalayan rivers.

Tree plantation and ecological transformation across coastal areas by the Bangladesh Forest Department can help mitigate coastal erosion and stabilize the newly formed islands. (Photo: Kabir Uddin/ICIMOD)

Tree plantation and ecological transformation across coastal areas by the Bangladesh Forest Department can help mitigate coastal erosion and stabilize the newly formed islands. (Photo: Kabir Uddin/ICIMOD)

Managing the new lands

What these new land formations mean for the Bangladeshi population is yet to be fully understood. Natural land expansion is expected to continue in Bangladesh, and the government has also been working on projects to reclaim land by taking advantage of the sediment flow. Increased land area could indeed relieve pressures on dense settlements, but the integrity and evolution of these new lands also need to be scientifically studied. Islands such as Bhola, Hatiya, Manpura, and Sandwip have experienced erosion in their northern parts. Soil erosion removes fertile topsoil and sedimentation can block inland river flow, disrupting navigation along rivers and causing floods. Bangladeshi settlements have popped up in new islands. The Government of Bangladesh has announced that it has built embankments to protect against storm surges, along with cyclone shelters, hospitals, and schools. Monitoring, feasibility studies, and appropriate interventions are vital if Bangladesh is to make good use of these new lands.

Vegetation growth on the new islands is good news for their sustainability. Vegetation growth and plantation of native species on barren islands could support biodiversity, protect from coastal erosion, and help stabilize the newly formed islands. This needs to be complemented by government- and community-led plantation efforts to mitigate erosion and sedimentation.

Short- and long-term land use plans can be formulated by identifying priority areas of soil loss. The government can establish remote sensing-based monitoring systems to biannually provide projections of future morphological changes along the coast. This will help identify erosion-prone areas where settlements will be at higher risk and prioritize the allocation of stable zones for resettlement.

Baseline studies are needed in the high-risk areas to determine the actual sources of erosion on the ground and sedimentation load, and where interventions can potentially be most useful in reducing erosion rates. Earth observation can play a vital role in monitoring these coastal morphological and ecological transformations and planning for the resettlement, restoration, conservation, and management of these newly formed islands. With proper monitoring, planning, and development, these islands could be a boon from the Himalaya to the coasts of Bangladesh.

Technology underpins research in the environment

The study cashes in state-of-the-art cloud computing technology – Google Earth Engine (GEE) and publicly available satellite data. ICIMOD and its partners in the HKH region have harnessed this technology in the Regional Land Cover Monitoring System (RLCMS) to operationalize the generation of land cover maps using a harmonized classification system on a near-annual basis. In developing the RLCMS, ICIMOD focused on collaboration and co-development with partner organizations to define different land cover typologies/classes, collect reference data samples, and validate results. Land cover maps for the HKH region spanning 2008–2018 have been produced under its SERVIR-HKH Initiative.

 

Kabir Uddin

GIS and Remote Sensing Specialist

Kundan Shrestha

Editorial Officer

Rajesh Bahadur Thapa

Remote Sensing and Geoinformation Specialist