Man-made flood protections, not climate change, are the main culprit in sea-level rise in southwest Bangladesh, according to new research conducted for the U.S. Navy’s Office of Naval Research.
The report from a team of scientists at Vanderbilt University is the first part in a wide-ranging, $7.5 million analysis of environmental stress and human migration scenarios in the low-lying South Asian nation.
Published this week in Nature Climate Change, the initial study finds that embankments constructed since the 1960s are primarily to blame for lower land elevations along the Ganges-Brahmaputra River Delta, with some areas experiencing more than twice the rate of the most worrisome sea-level rise projections from the United Nations’ Intergovernmental Panel on Climate Change.
That doesn’t mean global warming isn’t a serious threat to Bangladesh, which is generally considered among the nations most vulnerable to rising temperatures, said lead author Leslie Wallace Auerbach. Far from it. But, Auerbach noted, policymakers, military leaders and others need a firm hold on the science in order to respond to looming humanitarian disaster and be aware of the solutions that may or may not work.
Good intentions on Polder 32, and bad results
“I think that it’s really easy for people to latch onto something like ‘Global temperatures are increasing and causing sea levels to increase globally’ and conclude that Bangladesh is going to fill up like a bathtub. I think what people need to understand is that there is more to sea-level dynamics than just water rising,” Auerbach said.
“The findings of this paper demonstrate that long-term issues like global sea-level rise are certainly a threat to countries like Bangladesh. But our research demonstrates that we have a much more immediate threat on our hands, and that is one of proper land use,” she said.
Co-author Steven Goodbred Jr., an associate professor of earth and environmental sciences at Vanderbilt University, agreed. “The whole narrative in Bangladesh is, ‘See, look, here are the impacts of climate change.’ … What we want this study to do is be a very clear, well-documented scientific study that is the basis for understanding and having an intelligent dialogue about what is happening, what is not and why,” he said.
The study focuses on an area bordering the Sundarbans, a UNESCO World Heritage site made up of about 50 islands that, the scientists note, were cleared over time and embanked as part of an effort to boost food production. The islands, or “polders,” are still protected by embankments—but, the study notes, those earthen structures also cause elevation loss, along with poor drainage and other problems.
Using a fast-static global positioning system and precision instruments to survey land-surface elevations, the team focused on a particular island known as Polder 32, as well as the pristine Sundarban forest itself. They found a significant disparity between the two landscapes—between 1 and 1.5 meters—that represented 0.2 centimeter per year of relative elevation change over the five decades since the polder was constructed.
First, do no harm
That, the report noted, is “more than double the upper end” of IPCC projections.
“To an average person, maybe a meter or a meter and a half might not seem like a lot. But when you consider the IPCC’s projections for sea-level rise over the next hundred years, it starts to come into perspective a little bit,” Auerbach said.
Flooding brings routine devastation to Bangladesh, particularly to low-lying regions in the southwest part of the country. When Cyclone Aila struck in 2009, flooding breached more than 1,000 miles of river embankments and displaced about 100,000 people in the region.
The study discovered that embankments have exacerbated the problem of sea-level rise by diverting the natural flow of sediments that helped raise the level of surrounding islands. While there are management solutions to stabilizing the landscape, those solutions are not without challenges, Goodbred said, but the study notes that systematically breaching embankment sections to allow for delivery of sediment to the coastal sea might at least partially reduce problems.
Yet while the study focuses on man-made problems and solutions, Goodbred also noted that it will be key to understanding the impact that rising global temperatures will have on Bangladesh.
“What we’ve observed and documented has nothing to do with climate change to this point, but what has happened mimics many of the anticipated impacts of climate change and sea-level rise in the coming decades and century,” he said.
“It turns that what the paper documents is things we’ve been doing there already have started to reveal what one would predict would happen with accelerated sea-level rise,” Goodbred said. “It gives us a better idea of what to expect in the future.”
By Lisa Friedman and ClimateWire