“When you’re planning for the future of cities like Houston, it would be unwise to assume that the climate of the future is pretty much similar to what it’s been for the last 100 years or so,” said Kerry Emanuel, the author of the paper and a professor of atmospheric science at the Massachusetts Institute of Technology. “Even if the climate wasn’t changing, records of rainfall are too short, and the quality of them is too low, to really get a handle on flooding risks.”

Global warming will worsen hurricanes for two reasons. First, otherwise identical storms of all types—not just hurricanes—will retain more moisture in a warmer climate. “It’s one of the risks that we’re most confident of,” he told me. “The physics are so elegantly simple: Warm the air and it can hold more water.”

Second, global warming will make storms move slower. What made Hurricane Harvey so damaging was not its intensity but its longevity: The cyclone moved ashore, parked over Houston, and then rotated in place for three days. It became an atmospheric conveyor belt, picking up water from the Gulf of Mexico and raining it out over the Houston metropolitan area. These days of rain caused the city’s devastating inland floods.

In Emanuel’s study, global warming helped slow similar hurricanes down. Though tropical cyclones unleash some of the fiercest winds on Earth at their center, their movement across the surface of the planet—and thus their storm track—is determined by the slower high-altitude winds summoned by distant high- and low-pressure systems. This planetary engine is slowing down as global warming pushes land and ocean temperatures closer together.

“If [general circulation] slows down, then places near the coast will get more rain,” Emanuel said. “But the main reason our technique shows increasing rainfall is that there’s more water in the air.”

Emanuel conducted the study through the use of a computational tool he pioneered: embedding a hurricane and ocean model in a coarse, planetary-scale climate model. To determine the current climate’s propensity for a Harvey-like storm, he used three meteorological models (with the embedded hurricane tool) to simulate thousands of years of late-20th-century weather. Then, he used six different global climate models (each with the same hurricane tool) to simulate thousands more years of late-21st-century weather. By examining the models’ output of rainfall data and storm tracks, he could arrive at more accurate probability risks.

“This analysis provides strong evidence for why climate-change information should be incorporated into any plans for building Houston back stronger,” said Heidi Cullen, the chief scientist and director of the World Weather Attribution program at Climate Central, a nonprofit based in Princeton, New Jersey, in an email.