Floods endanger millions more people than previously estimated

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Satellites give researchers a better view of the problem

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Researchers previously estimated that the floods posed a serious threat to millions of people. According to a new study, there were 86 million more people living in flood-prone areas worldwide in 2015 than in 2000. Study published today in the magazine nature.


Thanks to satellite remote sensing, the researchers were able to create the most comprehensive dataset of floods ever observed. This suggests that more people have moved to the waterfront where they are at risk. The findings also suggest that outdated flood maps used to inform urban planning and insurance policies may underestimate the real-world risk of flooding.

Just in the last one month, shocking floods have claimed hundreds of lives China, Germany and Belgium. Within days, a year’s worth of rain flooded Zhengzhou, a city in China’s Henan province. record breaking rain Dams flooded all of Western Europe and nearly entire cities were washed away.

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“What really hits home is the urgency of the issue,” says Colin Doyle, one of the authors of the new study and director of technology at the flood tracking and risk analytics platform Cloud to Street. “It is imperative now that we tackle the issue of resilience – both to adapt to events and to build infrastructure as a safety net.”

According to new research, the proportion of people living in flood-prone locations has increased by 20 to 24 percent since 2000. This is ten times higher than the estimates of previous studies. This increase was driven by a few different factors.

First, satellites have given scientists a better view of flood events. In the past, most flood maps relied on models and not actual flood observations. Now, with more satellites in space and more cloud computing capability, researchers like Doyle have new tools.

For their comprehensive global study, Doyle and his co-authors were able to look at images taken daily by two of NASA’s satellites to study the floods between 2000 and 2018. He linked this with the population growth figures in the affected areas. their conclusions. (An interactive global flood database went live today to accompany the new study. On Database Website, you can explore the new maps put together by Doyle and his colleagues.)

The satellite data allowed Doyle and his co-authors to see more types of flooding than on typical flood maps. These include flooding from dam failures, melting snow and surface water flooding. On the other hand, modeling limits traditional flood maps to those hazards when rivers and other water bodies are swollen due to heavy rainfall.

But the increase in flood risk that Doyle and his colleagues document is not merely a reflection of technological advances. The new development seems to have become more concentrated in flood-prone locations. Population growth in those riskier areas outpaced global population growth over the same period. This is partly driven by poverty and a lack of other options for many vulnerable populations, notes the study.

While more accurate flood maps can give city planners a better idea of ​​where to build protective infrastructure, they can also tell them where. No to build in the future.

“The only option for some communities will be to manage their return from flood-prone areas,” writes Brendan Jongman, a senior disaster risk management specialist at the World Bank. nature.

Doyle and Jongman note, there is still more work to be done to improve flood maps for larger cities. The satellites had a hard time peeping down in densely congested areas. “If you’re above New York City and looking down, you’ll be looking at the tops of mostly all skyscrapers,” Doyle says.

New commercial satellites can take higher resolution images, but it is still expensive for researchers to access that data. And while the new satellites may be able to take a better picture, they won’t necessarily be able to get what researchers saw with NASA satellites as Doyle and his colleagues.

Hopefully, time will unlock those tools for researchers, too. They will need all possible help to forecast the risk of floods in the future. Climate change is raising sea levels and eating away at the beaches and river deltas that millions of people call home. Rising global average temperature may also soup up storm carry on further heavy rain in some areas. NS nature The study estimates that by 2030 even more people will be affected by dangerous floods.

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