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Does Climate Change Fuel Floods? It’s Complicated

Here’s why that question is hard to answer

Louisiana's August 2016 flood has destroyed over 40,000 homes and killed at least 13. (Coast Guard photo by Petty Officer 1st Class Melissa Leake)
smithsonian.com

It’s being called “a hurricane with no wind”—a catastrophic flood that has caused at least 13 deaths and damaged at least 40,000 homes. But Louisiana’s ongoing emergency is causing another kind of flood: An outpouring of concern that the cause is anthropogenic climate change. Is the flood in Louisiana (or, for that matter, others around the world) really the result of human activity? Here are five things to know:

Heavy rain is linked to climate change

The idea is simple, but sensible: Warming climate causes increases in water vapor—a greenhouse gas that can be found wherever humidity can be measured. This warms the atmosphere more and pushes the amount of water vapor even higher in a vicious cycle known as water vapor feedback.

Though other greenhouse gases warm the atmosphere, too, scientists now think that water vapor is a “major player” in climate change itself because of the amount of energy it traps. In a warming climate, all that water vapor above can translate to more rain on the ground. And Earth certainly doesn’t lack heat, with June 2016 clocking in as the hottest month on record. This month, Louisiana had record levels of so-called precipitable water—the depth of water in the atmosphere at any given time. And lots of precipitable water means lots and lots of rain.

Still, it’s hard to attribute climate change to human activity

Though climate researchers maintain that human-fueled climate change is affecting floods, it’s difficult to attribute that change to floods themselves. The problem lies in something called event attribution—the science of figuring out what’s to blame for different extreme weather events. Since there are so many factors at play when it comes to weather (everything from the circulation of the ocean to latitude and even sunlight), it can be difficult to tease out what’s a trend and what’s a situational issue.

While scientists have been able to connect some extreme weather events to climate change—as with this year’s flooding in Germany and France—at this point, researchers can only really say that climate change causes things like frequency and intensity of some weather events.

Government risk predictions often use outdated data—and that’s confusing

You’d think that organizations like FEMA, given certain climate trends, would be able to use predictive flood maps to figure out how these events might increase in the future. But that’s not the case, writes Chelsea Leu for WIRED: Insurance companies and FEMA historically use data that’s infrequently updated instead of relying on up-to-date numbers. So FEMA maps and predictions don’t reflect current-day climate conditions.

But that could change: This week, the National Oceanic and Atmospheric Administration released a new, supercomputer-driven modeling system that may help better predict and monitor streamflow and flooding.

Floods are really hard to predict

Who can actually predict floods? It’s extremely complicated. Not only are floods difficult to link to climate change, but they’re hard to model. Models often overlook smaller bodies of water and other relevant physical features while focusing on large tributaries, and flood modeling can be prohibitively expensive. Data from satellites can also take a while to be plugged into computer models, even ones that purport to be able to predict floods months in advance. And since everything from ground saturation to leaf cover can affect the outcome of a flood, it’s hard to make models as accurate as they could be.

Geographic location also makes a difference when predicting climate change-fueld flood risk. In 2012, for example, scientists asserted that places like Southeast Asia, India, eastern Africa and parts of the Andes are at the highest risk of these events. And even when high-waters are predicted, it can be hard to forecast their intensity—or, as Jason Samenow writes for The Washington Post, to communicate the danger effectively to the public.

Don’t give up on stopping climate change

Sure, predicting floods is complicated, but that's no reason to give up on actions that could halt climate change. As the picture evolves, the link between climate change and floods could become even more apparent since human activities add up over time.

After all, floods are only part of the picture of a warming future. People could sidestep catastrophes like food shortages, rising ocean levels, ocean acidification and drought by reducing carbon output, ditching fossil fuels and consuming less. In the best-case scenario, we may never have to figure out whether the natural disasters of the future were caused by humans—that is, if we prevent more of them from happening in the first place.

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