Climate change increased the rainfall from hurricanes Katrina, Irma and Maria by 4-9 per cent, and could cause up to 30 per cent more storm-derived rain in the future, reports a paper published in this week’s Nature. A separate Nature paper concludes that Houston’s urbanization increased the risk of substantial hurricane flooding by around 21 times. Together, these findings highlight how human activity influences hurricanes and their effects.

Climate change is expected to increase the intensity of the strongest hurricanes. However, the limited number of strong hurricanes in the observational record, combined with intense year-to-year variability, makes it difficult to determine how hurricanes have already been affected.

Christina Patricola and colleagues simulate how fifteen historically destructive hurricanes, including North America’s hurricane Katrina and Southeast Asia’s hurricane Haiyan, would develop in pre-industrial, modern, and three potential late twenty-first-century climates. They find that hurricanes Katrina, Irma and Maria had 4-9 per cent higher average rainfall and a greater likelihood of extreme rainfall than they would have had in a pre-industrial climate. However, storm intensities (based on wind speed and pressure at sea level) were not substantially affected. Predicted climate change could increase wind speeds and rainfall for most intense storms, increasing peak wind speed by 6-29 knots and resulting in 25-30 per cent more rainfall for some storms in the worst-case future emissions scenario.

In a separate paper, Gabriele Villarini and colleagues modelled how Houston’s urbanization affected rainfall during 2017’s hurricane Harvey, and find two effects. First, the city topography increased atmospheric drag, promoting heavier rainfall. Second, the urban surface increased flooding, probably because of extensive concrete and asphalt coverage. Together, urbanization increased the risk of Harvey-level flooding by, on average, 21 times (with risk increases across Houston varying from 0.1 to more than 90 times). The findings emphasize the need to consider flooding during urban planning.