State of the Planet

News from the Columbia Climate School

Risks and Choices as Populations Surge in Flood Zones, Rich and Poor

flood images

Humans are profoundly heating the climate and changing storm patterns through a surge in emissions of heat-trapping gases and other pollution. But there’s also been a simultaneous surge of settlement in zones prone to flooding — producing what some geographers call an “expanding bull’s eye” of exposure to climate-related threats like floods. And of course the poorest and most marginalized populations are always hurt most.

A pioneering study, published in Nature on Wednesday, has greatly raised estimates of population growth in flood-affected regions and offers sobering projections of much more flood exposure through 2030 without big changes in policy at every scale. Luckily the work, sifting millions of high-resolution satellite images, has also produced a new open-access tool, the Global Flood Database, that offers officials, the financial world and communities a clearer view of the exposure they’ve created and a chance to shape safer development paths in the critical years ahead.

In a live Sustain What webcast on Friday, August 6, at noon U.S. Eastern time, join host Andy Revkin of the Columbia Climate School and in a brisk solution-focused discussion with the paper’s lead author, Beth Tellman, and top experts from as far afield as Bangladesh and South Africa.

Tellman conducted much of the satellite work while a postdoctoral fellow at Columbia’s International Research Institute on Climate and Society. She’s moving to the University of Arizona this summer and is also a co-founder and chief science officer of Cloud to Street, a public benefit company that built the database used in the research.

The other guests are Jean-Martin Bauer, senior digital advisor for the U.N. World Food Program and the program’s former country director of Republic of the Congo; Saleemul Huq, director of the International Centre for Climate Change and Development; Catherine Sutherland, associate professor in development studies, University of KwaZulu-Natal; and Simon Young, senior director (focused on climate and resilience) at the global advisory company Willis Towers Watson.

There’s no need to sign up. Just add this link to your preferred calendar and click to watch three ways. Or watch here on YouTube:


Here’s an excerpt from Revkin’s Bulletin post on the paper and related issues:

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

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 areas that flooded 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 this week in the journal Nature.

That influx, researchers say, 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 concluded.

Explore the details in a post on the research from Columbia University’s International Research Institute on Climate and Society, where the lead author, Beth Tellman, did much of the work.

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.

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.”


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 examples looking at reported adaptation funding and comparing it to their findings. Here’s one:

“Central African 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.”

Read the rest here.

Banner featuring a collage of extreme heat images.

Recent record-breaking heat waves have affected communities across the world. The Extreme Heat Workshop will bring together researchers and practitioners to advance the state of knowledge, identify community needs, and develop a framework for evaluating risks with a focus on climate justice. Register by June 15

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