New sea-level rise projections alarming for Southeast Asia

Coastal land is home to some 42 million people in Bangladesh, 31 million in Vietnam and another 26 million just in the Chinese city of Shanghai. A new report on sea level rise, published Tuesday in Nature Communications, doesn’t have a lot of good news to offer any of them.

That’s because the authors, Scott Kulp and Benjamin Strauss of Climate Central, warn that their more-accurate estimates of sea level rise triple the estimated risk of coastal flooding around the globe. The numbers are derived from CoastalDEM, a digital elevation model (DEM) they say delivers better data for Southeast Asia and other parts of the world that haven’t had the same quality of sea level projections seen in Europe and the West.

And what they’re seeing is a lot more people at risk than previously thought.

“As sea levels continue to rise throughout the century, chronic flooding will spread and more land will be permanently lost to the ocean,” the authors explain. “By 2100, CoastalDEM’s elevation data show, land currently home to 200 million people could fall permanently below the high tide line.

“The bad news is again concentrated in Asia,” they added. “China, Bangladesh, India, Vietnam, Indonesia, and Thailand are home to the greatest number of people who today live on land that could be threatened by permanent inundation by 2100—151 million in total, and 43 million in China alone.”

Asians are joined by people in 19 countries, including Nigeria, Brazil, Egypt and the United Kingdom, where at least one million people currently live on land that’s at risk of being permanently inundated. The well-documented risks to island nations, such as Maldives, also may be far worse than thought.

What Kulp and Strauss did was compare the CoastalDEM projections with those of the SRTM, which was developed from NASA satellite data nearly 20 years ago. The SRTM has its flaws, including known errors linked to topology, vegetation, buildings and other factors that alter the accuracy of land elevation data. Climate Central’s CoastalDEM reduced the noise while adding in flood, tide and related information.

In all, there are 23 variables and three carbon emissions scenarios (RCP 2.6, 4.5 and 8.5) incorporated, respectively, into the CoastalDEM model and the published research findings. When the authors compared the new numbers with the previous SRTM estimates, they saw a sobering shift in the risk.

Mainland China, for example, sees the projection for people living in 2050 at an elevation below the average annual flood line go from 29 million to 93 million. Bangladesh, India, Vietnam, Indonesia and Thailand all see tens of millions included in vulnerable coastlines in the moderate scenario. The human toll is haunting, but so are economic impacts to global cities and their infrastructures.

“Even with low carbon emissions and stable Antarctic ice sheets, leading to optimistically low future sea levels, we find that the global impacts of sea-level rise and coastal flooding this century will likely be far greater than indicated by the most pessimistic past analyses relying on SRTM,” the authors said.

“If our findings stand, coastal communities worldwide must prepare themselves for much more difficult futures than may be currently anticipated.”

To see the sea-level rise hotspots on an interactive map, click on the Bangkok flood map below.