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First-of-its-kind study finds Hurricane Harvey hit Latinos the hardest

Researchers have connected climate change to extreme weather in the past. Now they can assess who’s most affected.

Addicks Reservoir flows into neighborhoods from floodwaters brought on by Tropical Storm Harvey in Houston. (David J. Phillip/AP)

Scientists have long known that warming temperatures supercharged the rainfall from Hurricane Harvey. But now in a landmark new study about the 2017 hurricane, they’ve gone a step further. In the new research, released Thursday in the journal Nature Communications, scientists showed not only that climate change greatly increased Harvey’s flooding but also that the climate-boosted flooding hit low-income Hispanic communities the hardest.

The finding shows that researchers can now do more than quantify how climate change led to additional homes being flooded. They can also assess how weather extremes, propelled by climate change, harm some groups more than others.

“There is now a clear line between how human beings have affected the environment to how that could impact a particular storm or event, and how that affects the most vulnerable communities,” said Daniel Gilford, a climate scientist at the nonprofit Climate Central who was not involved in the Harvey study. “And I think this paper does an excellent job of making that connection.”

Once upon a time — or about two decades ago — scientists often said that they could not connect any given hurricane or other weather extreme to climate change. The science didn’t exist yet.

Gradually, researchers began to use models for two separate climate systems: one with human-induced global warming and one without. By comparing extreme weather events in the two different worlds, scientists can now say how climate change has influenced the likelihood or severity of particular heat waves, droughts, floods and hurricanes.

But it’s only recently that scientists have also begun to track climate change’s fingerprints on the impacts of given events: quantifying the number of homes flooded by climate change, for example, or billions of dollars in damage done. Last year, researchers estimated that global warming was responsible for at least $8 billion of Hurricane Sandy’s damage in New York City and the surrounding areas.

When Harvey doused Houston, it also filled Billy Guevara’s home in the city’s northeast with 17 inches of floodwater. Guevara, who is blind, remembers his seeing-eye dog perched on a grooming table to stay out of the rising waters; he remembers being without power for four days as the water crept up his driveway; he remembers being crushed by the news that a few miles away, several of his cousins and his aunt and uncle had been swept away in their van by the floods.

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But he also remembers the smell. “Like a wet dog,” he said. “Just damp.”

Five years after Hurricane Harvey, Guevara, 48, has little doubt in his mind as to one of the main causes of the disaster he experienced. “I blame a lot of this on global warming,” he said. “There’s no doubt about it.”

For the new study on Harvey, scientists built on research that quantified how much of the hurricane’s rainfall was due to temperature change from the burning of fossil fuels. (Warmer air holds more moisture, which can lead to more intense rainfall during hurricanes.)

On the low end, researchers estimated that global warming was responsible for about 20 percent of the precipitation that fell during Harvey; on the high end, that figure could be as much as 38 percent. When the scientists plugged those numbers into a flood model, they found that climate change had increased the depth of the flooding between 8 and 10 inches.

For somewhere between 32 percent and 50 percent of homes, those eight to 10 inches were the difference between the home flooding and the home coming out of the hurricane unscathed.

“The first big finding is that climate change can serve as the tipping point between flooding and not flooding,” said Kevin Smiley, a professor of sociology and Louisiana State University and the lead author of the paper. “That extra few inches could mean the difference between having a very soaked lawn and having a few inches of water in your home — which could mean thousands of dollars of damages.”

Researchers then analyzed how different groups were affected by the flooding. According to the study, neighborhoods with more Latino residents also see more flooding attributed to climate change. For example, Latino households make up only 36 percent of the properties in Houston that did not flood during the hurricane. They also accounted for 48 percent of the properties that flooded because of climate change, as well as 50 percent of the properties that would have flooded anyway.

The researchers did not attempt to identify the precise causes of the disparity, but environmental justice advocates have long argued that poor drainage and outdated infrastructure can magnify flood damage in low-income neighborhoods.

According to Smiley, that’s a clear demonstration of how climate change is exacerbating existing inequalities. “The core question of the entire study was, who bears the brunt of climate change?” Smiley said. “When you have these disproportionate impacts, it raises questions about the urban development processes that contributed to it.”

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The study also showed that areas outside the Federal Emergency Management Agency’s 100-year flood plain also suffered greater climate-change-induced flooding. The 100-year flood plain designates areas that FEMA believes have a 1 percent chance of flooding in any given year. Homeowners with federally backed loans in these areas are required to purchase flood insurance.

But because many of the damaged homes were outside the flood plain, Smiley worries that many homeowners did not have flood insurance. “Outside the flood plain, you may not even be aware that you’re at risk,” he said. “You may not have even thought about purchasing flood insurance.”

Guevara’s home had flooded once before, during Tropical Storm Allison in 2001, so he knew that there was some level of risk. But neither he nor his mother, who lived next door, had flood insurance by the time Harvey rolled around. “They said we weren’t in the flood plain, so it wasn’t necessary,” he said in a phone call. “We let our flood insurance lapse — we couldn’t afford it anymore.”

Smiley and one of his co-authors, Michael Wehner, a senior scientist at the Lawrence Berkeley National Laboratory in Berkeley, Calif., say that they mostly want the study to inform the public and also to spur places such as Harris County — which encompasses Houston — to address underlying socioeconomic inequalities.

But both also note that similar studies could be used for litigation — one of the original goals of what’s known as attribution science. Now that scientists can trace specific damage to climate change, it may be possible to someday sue fossil fuel companies for helping to spew greenhouse gases into the atmosphere. So far, similar lawsuits haven’t made it far in the U.S. context. But with the United Nations focusing more on the idea of “loss and damage” for climate-related disasters, such research could become increasingly useful.

“It’s not a decision for me to make, obviously,” said Wehner. “But this is a defensible way to establish losses and damages.”

The prospect of another flood is never far away. “It’s always in the back of our minds whenever a system comes into the Gulf,” Guevara said. “There’s always the fear.”