Climate change made floods from Hurricane Harvey up to 50 per cent worse

In August 2017, Hurricane Harvey hit the Texas Gulf Coast, dropping nearly four feet (1.2 metres) of rain on Houston, nearly five feet (1.5m) of rain in other parts of the state, as the storm lingered for days.

The flooding that ensued was catastrophic, with vast parts of the Houston area underwater for days. In the aftermath, more than 100 people died.

Now, a new study has revealed that the damage from the storm was made significantly worse by the climate crisis.

A warmer planet caused Harvey to hold even more rainfall, the researchers found. And without all that extra rainfall, up to half of the areas that flooded in Harris County - home to the major city of Houston - would have stayed above water.

“Climate change is happening right now with real and substantial costs,” Kevin Smiley, a sociologist at Louisiana State University and one of the study’s authors, said via a press release.

“Three to five extra inches of rainfall from climate change can make the difference between your lawn getting soaked and your house getting flooded leaving it uninhabitable.”

Global heating is super-charging hurricanes. Higher ocean and air temperatures mean storms can hold a lot more water, which they later dump as massive amounts of rainfall, like the record-breaking and devastating rains that came with Hurricane Harvey.

The new paper looked at how much rain would have fallen during the hurricane in a hypothetical world where the climate crisis didn’t exist. They focused on two scenarios in such a world — either that the storm would have had about 20 per cent less, or about 38 per cent less rain.

If the storm had caused 38 per cent less rain, 50.6 per cent of all the buildings that flooded in Harris County wouldn’t have flooded at all, the study found. Even in the lower scenario, with 20 per cent less rain, 31.9 per cent of the homes that flooded would have stayed above water.

This added up to $3.7billion in additional damages, the study, published on Thursday in the journal Nature Communications, noted.

These climate-induced impacts also hit some communities in Harris County more than others. Of the properties that only flooded because of the climate crisis, 48 per cent were associated with Hispanic groups, the researchers estimated. About 33 per cent were associated with white residents, 13 per cent with Black residents and 7 per cent with other racial or ethnic groups.

In comparison, only 36 per cent of the properties that didn’t flood were associated with Hispanic groups — with 37 per cent associated with white residents. About 18 per cent were associated with Black residents and 9 per cent with other racial or ethnic groups.

According to the US Census Bureau, Harris County is about 44 per cent Hispanic, 28 per cent white (not Hispanic) and 20 per cent Black. The researchers called this study “a first of its kind investigation” into how climate-driven impacts might have affected different groups in different ways, via their press release.

Many homes in Harris County were built without taking flood risk into account. According to a ProPublica/Texas Tribune article published before Hurricane Harvey, over 7,000 residential properties were built between 2010 and 2016 in the 100-year floodplain, the area that could expect a flood about once every 100 years.

The climate crisis was why many homes in those flood plains were left underwater, according to the new study. But it left even more homes outside the floodplains underwater. In total, 76.1 per cent of flooded properties were outside the floodplains, the researchers note.

The research builds on other “climate attribution” studies that investigate how much planetary warming has worsened recent disasters.

Another study from World Weather Attribution, a group of climate scientists who regularly do this kind of work, found that the climate crisis made Harvey’s record rainfall three times more likely to have happened and 15 per cent more intense.

While the 2022 hurricane season in the Atlantic has gotten off to a slow start, the National Oceanic and Atmospheric Administration (NOAA) has predicted an above-average year, with up to 20 named storms and five major — meaning Category 3 or higher — hurricanes.