Exposure to flooding is 10 times higher than previously thought, study finds

In Germany, severe flooding claimed the lives of at least 173 people. In Nigeria, Lagos Island has experienced one of its worst floods in recent years, submerging cars and homes. And, earlier this week, officials announced that the death toll from the July floods in China had risen to 302, more than triple the previous estimate.
“It’s no surprise that we are seeing some really big floods that are potentially unprecedented and affecting countries like China,” said Beth Tellman, lead author and co-founder of Cloud to Street, an analytics company who developed the Global Flood Database used as the backbone of new research, CNN said. “This is exactly what the climate models predicted.”

Scientists from Cloud to Street, NASA, Google Earth and universities analyzed global flood exposure using satellite observations, creating the largest flood dataset ever produced that maps the maximum extent of water during 913 major floods between 2000 and 2018.

“It’s great to have such a database on which you can now test your model, especially on a global scale,” Guy Schumann, a researcher not involved in the study, who specializes in flood data and modeling.

“Everyone now wants to know what’s going on in the world, when traditionally these databases or observations were only available at scales of measurement in the field of a local scale or, at best, at a national scale. “

Using the database, scientists identified where the major flooding has occurred over the past two decades. They found that nearly 90% of the flooding occurred in South and Southeast Asia, especially China and India, places where migration has increased significantly since 2000.

Tellman, who has been working on this research for five years, said it was “shocking” to see the increase in flooding where the population has also skyrocketed. And floodplains are now found more frequently in urban areas, she said.

“It was kind of the big ‘aha!’ moment for us, “said Tellman,” where we are like “there’s a really serious problem with the development of the floodplains. “”

From 2000 to 2015, around 58 to 86 million people moved to flood-prone areas, they found, translating to an increase of about 20% in the flood-prone population. The flooding and the number of people at risk will continue to worsen, the study says. Thirty-two countries are already experiencing increasing flooding, and 25 new countries will be added to this list by 2030, unless greenhouse gas emissions are significantly reduced, the researchers found.

Low-income communities are often the most at risk, as they usually have no choice but to move to areas that are less favorable, cheaper and more prone to flooding.

“It’s not like people necessarily want or choose to live in a high risk place, but they may not have any other option or public housing program in their country,” Tellman said. .

The Cloud to Street study mapped floods and their duration around the world. The rain caused 86 days of flooding in South Asia in 2007, displacing millions of people in India, Nepal, Bhutan, Pakistan and Bangladesh, according to the global flood database Cloud to Street.
In 2007, for example, flooding from a deadly cyclone killed around 1,000 residents and displaced 9 million people in Dhaka, the capital of Bangladesh. During this period, analysis shows that Dhaka also experienced an increase in population in poor areas prone to flooding.

Beyond flooding due to heavy rains, tropical storms and snowmelt, the database also takes into account floods caused by dam failure. While they accounted for less than 2% of floods, dam failures experienced the largest increase in frequency from 2000 to 2015 – 177% – which exposed vulnerable populations. Tellman said it was probably because of what hydrologists call the “levee effect.”

“When we have infrastructure like a dam or a dike, people feel safe and feel like this land is protected, so its value goes up, and we build things on it,” she said. “The problem is, if the dam is not maintained it can become a huge danger and affect so many people.”

In 2008, the dikes along the Koshi River collapsed and destroyed the homes of more than 3 million people in India and Nepal. In 2018, heavy rains and a water leak from the Bagre Dam in Burkina Faso flooded thousands of hectares of farmland in neighboring Ghana, exacerbating food insecurity in the region.

Researchers say such incidents demonstrate the deadly cost of failing infrastructure, exacerbated by climate change.

Victims crossed floodwaters along the Koshi River in Nepal in 2008.

Philip Ward, professor of global water risk dynamics at Vrije Universiteit Amsterdam, told CNN that the study findings underscore the importance of sustaining aging infrastructure and building resilience. He also said the findings suggest officials should devote more resources to the warnings.

“We have to make sure that there are always early warning systems, evacuation plans and good communication between the most vulnerable, politicians, emergency responders, etc.,” said Ward, who did not participate in the study.

Satellite observations capture realities that are not often captured by predictive climate models, according to Tellman.

Most maps of flood-prone areas, including those used by government agencies like the Federal Emergency Management Agency, rely on models that simulate flooding based on historical data, the results of which may be limited due to climate change. pushes floods to unprecedented territory.

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Outside experts said Cloud to Street’s population analysis would strengthen the data they already have, especially as the climate changes.

“The most important thing about this research is the database itself,” Ward said. “As someone who models flood risk, this data will really allow us to better validate models and compare models to reality.”

As climate change fuels more extreme and larger-scale flooding, Tellman hopes the new analysis will encourage policymakers to invest in equitable climate adaptation measures in places where flood exposure has increased more rapidly. than the surrounding population.

“Who is affected by the flooding is really in our control,” Tellman said.

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