Satellite images signal rising flood risks in Bangladesh
The number of people living in the floodplains of Bangladesh has increased significantly along with the catastrophic risks that come with floods, according to a report based on analysing satellite observations.
A team of researchers from Penn State, Curtin University, and the University of Chittagong recently analyzed satellite observations of nighttime lights and land use to track population growth in flood-prone areas.
In June 2022, they reported that roughly 70 million people in Bangladesh now live in flood-prone areas (within 2 kilometres of a river), about 1.5 million more than in 2000. In Dhaka, about 6 million people live in flood zones.
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The researchers based part of their analysis on nighttime observations from the Operational Linescan System (OLS) on US Defense Meteorological Satellite Program satellites and the Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi-NPP satellite. Cities throughout Bangladesh saw increased light in floodplains throughout the country from 2000 to 2018. Dhaka, Chattogram, Khulna, Sylhet, and Mymensingh were among the cities with pronounced increases.
"The total nighttime light luminosity within 2 kilometres of rivers increased by 235% throughout Bangladesh," said Arif Masrur, the Penn State University geographer who co-authored the study.
"As the population grows, the scarcity of land is fueling unplanned development in floodplains. More people are moving into floodplains to farm rice or fish, or to simply have somewhere to live," he added.
However, the number of people living in the risky zones is definitely larger than the nighttime luminosity data suggests.
"It is safe to assume that many households within 2 kilometres of rivers lack connections to the electrical grid," explained Ashraf Dewan, an environmental geographer based at Curtin University and co-author of the study.
"While OLS and VIIRS can detect whole villages reliably, the sensors don't always detect more isolated homes or homes that use power sparingly to save money, particularly in areas with lots of vegetation," he noted
The capital city, Dhaka, is surrounded by rivers and tributaries: the Buriganga to the south, the Turag to the west, the Tongi Khal to the north, and the Balu to the east.
It saw a boom in its population from 5.7 million people in 1988 to more than 22 million at present. According to one recent analysis of Dhaka's population since 2000, growth has been particularly rapid along the Buriganga and the Balu rivers.
Floods in 1988 swamped Dhaka and led to the deaths of more than 2,000 people. Another catastrophic flood in 1998 killed 900 people and caused $3.5 billion in damages.
In some parts of the low-lying city, shanty towns and other informal settlements have pushed into ephemeral wetlands, known as khals, sharply increasing the risks from damaging monsoon season floods. A prime example is Korail, a poor neighbourhood that has spread into a lake. Homes are built on stilts and the neighbourhood routinely floods during heavy rains.
"We hope this research makes the scale of the issue clear for policymakers," said Dewan. "If this trend continues, more homes will be destroyed, and more lives will be lost."
