People living in low-lying coastal regions in Bangladesh are already moving to escape sea-level rise. A new study predicts the cascading effects of this migration will ultimately affect 1.3 million people across the country by 2050.
The new study presents a mathematical model of human migration that considers not just economic factors but also human behavior—whether people are unwilling or unable to leave and if they later return home. It also considers the cascading effects of migration, as migrants repeatedly move to find new opportunities and original inhabitants are displaced.
The findings are published in Earth’s Future, AGU’s journal for interdisciplinary research on the past, present and future of our planet and its inhabitants.
“We are not only looking at a snapshot, but we are trying to reconstruct the trajectory of the migration and looking at its evolution,” said senior author Maurizio Porfiri, an engineer at the Center for Urban Science and Progress at the New York University Tandon School of Engineering.
According to the new model, the districts in the south along the Bay of Bengal will be the first to be impacted by sea-level rise, causing a migration that will ripple across the country and affect all 64 districts. Some migrants will likely be rejected by the existing residents—or displace them—triggering further migrations. While the population of the capital, Dhaka, initially will surge, the results suggest that movement away from the inundated capital region will ultimately cause its population to shrink.
Bangladesh is especially susceptible to sea-level rise because it is a low-lying country crisscrossed with rivers and already experiences frequent flooding during the summer monsoon season. Its coastline on the Bay of Bengal measures about 580 kilometers (360 miles), with a large portion consumed by the Ganges river delta. An estimated 41 percent of its 163 million people live at elevations lower than 10 meters (about 32 feet).
The authors emphasize that the new model can be used to study migration in response to any environmental disturbance that causes unrest, such as droughts, earthquakes or wildfires. Additionally, it is relatively simple and can make reliable predictions based on little data.
Human dimension to economic models
The new model builds on a previous human migration model that focused on economic migrants in Bangladesh and it uses the same set of geographic and demographic data.
The previous study predicted that the central region of Bangladesh, including its capital, Dhaka, would receive the greatest number of migrants. The new study agrees, but finds that the ripple effects from that migration will ultimately cause people to leave the capital, leading to a population decline.
“Accurately predicting migration flows in data-limited settings will be critical for avoiding conflict and resource scarcity in likely destinations,” said Kyle Davis, an environmental data scientist at the University of Delaware. Davis was a lead author on the previous migration model but was not involved in the new work. “This study provides an important step towards ensuring that migration occurs sustainably and in a way that ensures human welfare.”
Worldwide, more than 600 million people living in coastal regions are at risk of being displaced by sea-level rise due to climate change. Flooding from tropical cyclones and saltwater intrusion into groundwater is also robbing people of their homes and livelihoods.
The outputs from the model can help governments plan and prepare for the impacts of sea-level rise and other environmental disturbances by allocating resources to the most hard-hit regions and ensuring that cities are adequately equipped to deal with the influx of migrants.
“Mathematical modeling is the only way we have to ground our future decisions,” said first author Pietro De Lellis, an engineer at the University of Naples Federico II. “Migration has lots of sources—environmental disasters, political tensions—but in the end, we need to use science to provide useful tools for decision-makers.”
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