People navigate their way through a flooded street as it rains in Mumbai, India. The number of people threatened by flooding triggered by climate change is about three times higher than previously thought, a new study says. (Rajanish Kakade/AP)

The number of people threatened by climate change-triggered flooding is about three times higher than previously thought, a new study says. But it’s not because of more water.

It’s because the land, especially in Asia and the developing world, is several feet lower than what space-based radar has calculated, according to a study in the journal Nature Communications Tuesday.

So instead of 80 million people living in low-lying areas that would flood annually by 2050 as the world warms, this new study finds the population at risk is closer to 300 million people.

And if emissions of heat-trapping gases continue unabated and Antarctic ice melts more in a worst-case scenario, around 500 million people could be at risk by the end of the century, according to the study by Climate Central, a New Jersey based nonprofit organization of scientists and journalists.

Space-based radar says 170 million are at risk in that scenario.

For big picture global mapping of flooding threats, the go-to technology for elevation is NASA’s Shuttle Radar Topography Mission. But that doesn’t accurately show ground, instead mistaking rooftops and tree canopies for ground with an average error of 6 1 /2 feet, said Climate Central Chief Executive Officer Ben Strauss, a scientist who studies sea-level rise.

For the United States, much of Europe and Australia, this is not a problem because those areas use airborne lidar radar, which is more accurate about true elevation. But in flood-prone Asia and other places, that’s not an option, Strauss said.


Phon Tongmak, a rubber tree farmer, adjusts a cup at his flooded rubber plantation in Nakhon Si Thammarat Province, Thailand, in 2017. Areas in Asia and the developing world will flood more regularly because they are several feet lower than what space-based radar has calculated, according to a study in the journal Nature Communications. (Surapan Boonthanom/Reuters)

So Climate Central used the shuttle radar, artificial intelligence and 23 variables to create a computer model that is more accurate in globally mapping elevation, Strauss said. They then tested it against the airplane-generated data in the United States and Australia and found this computer model was accurate, he said.

“This is a far greater problem than we understood,” Strauss said. “Far more people live in risky places today than we thought, and the problem only multiplies in the future.”

He said the new model found “a huge difference” in elevation in places such as Shanghai, Ho Chi Minh City, Bangkok, Jakarta and Mumbai.

Five outside sea-level rise experts said the study highlighted a problem with current data, especially in Asia.

“This study represents very significant progress in the understanding of the risk which climate change-related sea level will cause for hundreds of million of people before the end of this century,” said Jean-Pascal van Ypersele of the Catholic University of Louvain in Belgium. “If hundreds or even tens of millions of people are flooded in Asia or Africa, it will create social and economic disruptions on a huge scale.”