Study Finds Global Surge of Flood Exposure is from Population Shifts Far More than Climate Change

Too often, rising climate risk is conflated with rising CO2. That takes the heat off national and local leaders who can cut drivers of risk on the ground now.

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A High-Resolution View of Crowding Flood Zones

A pioneering study of nearly two decades of high-resolution satellite imagery and population data shows dozens of countries, rich and poor, are amplifying flood risk on the ground far faster than climate change is adding to it.

The main driver is rapidly shifting population dynamics, with the research team estimating that up to 86 million people moved into observed flood regions around the world between 2000 and 2015. In fact, populations in the assessed flood-prone regions grew 24 percent faster than outside those areas - more than 10 times previous estimates, according to the study, published August 4 in the journal Nature.

That shift is driven by a mix of the promising tug of urbanization, much of it along waterways or coasts, and the devastating shove of entrenched disregard or prejudice forcing tens of millions of poor or marginalized people into vulnerable floodplains or steep slopes even within today's otherwise-prosperous communities.

Through 2030, under any scenario for heat-trapping CO₂ emissions, population growth and paving in flood-prone regions will continue to amplify the danger posed by floods like those making headlines every week, the authors conclude.

Explore the details in a post on the research by Columbia University's International Research Institute on Climate and Society, where the lead author, Beth Tellman, did much of the work. (She's moving to the University of Arizona this summer.)

The new study, which made the cover of the journal, adds a scary layer of detail to a hidden facet of the climate crisis that geographers have warned about for more than a decade: Communities worldwide are building exposure to floods far faster than climate change is affecting flooding.

[Also read my August 6 post: Behind Global "Climate Emergency" Rhetoric, Solvable Vulnerability Emergencies Abound]

The detail comes from five years of collation and analysis of millions of high-resolution satellite images and data reflecting changing local populations. Most studies gauging flood risk, including those used by the Federal Emergency Management Agency in the United States, have relied on static models.

Identifying the core drivers of climate risk, as this study does for population, is a vital first step toward turning knowledge into impact where it's needed. The work is a great example of what the longtime Columbia University climate researcher Adam Sobel calls "usable science."

With utility in mind, the lead authors have founded a public benefit company, Cloud to Street, that has created an open Global Flood Database that can help countries, communities and companies identify and address sources of risk.

Sobel, who was not part of the study, said: "It's a state-of-the-art attempt to combine satellite flood observations, climate model projections, and population estimates to see trends in flood risk, and the conclusions are compelling."

Significance

The study hopefully will hammer home that while cutting planet-heating emissions is vital to limit the worst-case fat tail of climate danger, that can't distract from the urgent, and largely unmet, responsibility to cut risk on the ground, particularly for the most vulnerable communities, marginalized by poverty or prejudice.

In an email exchange, Tellman offered this observation (some shorthand cleaned up):

"What this database and analysis shows is that regardless of a changing climate, we are seeing very large changes in human populations newly settling in places that have recently flooded. This is not really a climate problem. It's pretty clearly a problem in our own governance, social, economic, and political systems that fail to buy out homes after floods, enact strict zoning, or provide public housing for populations that have no other choice. While climate change clearly exacerbates the problem, this flood exposure problem is already well entrenched."

In an email sent to me and other journalists, Tellman said she hopes the findings and database can spur developed countries to do a better job of targeting adaptation funding and capacity where it’s needed most. She pointed to several jarring example looking at reported adaptation funding and comparing it to their findings. Here's one:

“Central Africa Republic is only receiving $10 million in adaptation funds - meaning there are 106 countries receiving more money!," Tellman wrote. “Yet our data show this country has the HIGHEST expected increase in proportion of population exposed to floods (increases expected up to 87%!). It has also had recent increases in flood exposure - by 76% from 2000-2015 looking at the satellite data.”

The Big Picture

The study and flood database out today are just part of a growing global effort to use vast volumes of open data to reveal forces impeding sustainable human advancement. Global Fishing Watch, Earthrise Alliance and the new Impact Observatory are just a few of many others.

Backed by such data sources, communities everywhere hopefully can more effectively demand the change politicians and builders and financial powers seem so reluctant to pursue.

That's still the hardest part, said A.R. Siders, a University of Delaware assistant professor focused on disaster policies reducing vulnerability before the worst happens.

"The hope is that studies like this one - studies that highlight the massive scale of the problem - motivate governments (and businesses, and civil society, and residents) to take action: to make reducing flood risk a priority and to devote serious resources to the challenge," she wrote in an email.

But she stressed there's a long road ahead, and floods won't wait.

"Understanding where the floodwaters are is one step," Siders said. "It takes another step to understand what that means for people - whether a flood means a few inches of pooled water in the house or life-threatening torrents washing homes away. And there's another step after that to understand how people want to address the problem."

Engage

Join me in a live Sustain What video chat Friday at noon U.S. Eastern time with Tellman (who describes her mission as "socializing the pixel") and three independent experts focused on the intersection of climate data, risk and [in]decision.

Post questions or comments ahead of time below or join us Friday. There's no signup. Just paste this link in your calendar for the day and time to watch and engage on YouTube, LinkedIn or Facebook.

Perspectives

I sent the paper around to an array of researchers representing an array of perspectives, disciplines and vantage points (from Bangladesh to South Africa to Louisiana).

I'll be posting more in an update on Friday, but here is one important thought to prime the pump.

Catherine Sutherland, an associate professor in development studies at the University of KwaZulu-Natal in South Africa, said the physical science and exposure maps in the Nature study are excellent, but worried that some of the assumptions about forces driving risk are flawed - particularly from the vantage point of Africa.

She zoomed in on this line from the paper: “We found that economic development and people moving into flood-prone areas is significantly increasing the number of people exposed to floods in those regions.”

In an email, Sutherland wrote: "I would argue it is not economic development but rather the lack of economic development and increasing poverty and inequality that is leading to increasing numbers of people being vulnerable to flooding."

My sense is that Tellman actually concurs on this point. We'll learn more Friday.

The paper by Tellman and colleagues certainly shows the sobering reality across the continent of Africa, which has the highest increase in the proportion of populations exposed to flooding.

Afterthought

I can't ponder the new study without thinking of the pioneering work of the innovative geographers Walker Ashley (Northern Illinois University) and Stephen Strader (Villanova) on what they aptly call the "expanding bull's eye" effect.

They have found the same risk-amplifying pattern in inland and coastal flood zones, wildfire zones and Tornado Alley (where there's no obvious signal of global warming and a stark signal of built vulnerability). This human habit isn't restricted to our relationship with climate. Strader has charted the exposure surge in volcano danger zones as well. Hello, Portland and Seattle!

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