Urban growth in Sylhet is shrinking water bodies, raising flood risks: study

Rapid urban expansion in Sylhet has dramatically reduced the district's water bodies over the past two decades, heightening the risk of flash floods and underscoring the need for stronger drainage infrastructure, a new study by Naturehas found.

The northeastern district, prone to sudden flooding due to its rugged terrain and intense rainfall, has seen water bodies shrink by about 77% between 2000 and 2023, while urban areas grew nearly fourfold, researchers said.

"Urban growth has come at the direct expense of natural water storage," the study said, warning that the loss of wetlands and ponds has weakened Sylhet's capacity to absorb excess rainwater.

The analysis, conducted using Google Earth Engine and Landsat satellite data, tracked land use and land cover (LULC) changes over 23 years. It found that urban areas now account for about 18.5% of the district, compared to less than 5% in 2000. By contrast, water bodies have declined from 34% to below 8% in the same period.

Researchers also identified Sylhet Sadar, Bishwanath and Golapganj as hotspots of urban growth, while upazilas such as Bishwanath saw water body losses of nearly 90%.

The changes are being driven by population growth, unregulated land development and climate-linked events such as flash floods. In 2004, an early flood caused a sharp spike in barren land across the district, the study noted.

Urbanisation without adequate drainage planning has left Sylhet more vulnerable to flooding, as reduced northern water storage channels excess flows to the south.

"Mitigating flash flood risks will require sustainable urban planning and investment in drainage infrastructure," the researchers said, adding that unchecked expansion could worsen waterlogging and labour unrest in flood-prone areas.

The findings, they said, offer policymakers and engineers evidence to design strategies that balance development with environmental protection.