Huge offshore wind farms can protect vulnerable coastal cities against devastating cyclones like Katrina and Sandy by tempering winds and ocean surges before they reach land, a study says.
Had such installations existed at the time, Hurricane Katrina, which ravaged New Orleans in 2005, and Sandy, which smashed the coastlines of New York and New Jersey in 2012, would have been reduced to strong but not devastating winds, it said.
"The little turbines can fight back the beast," said Cristina Archer, an associate professor of Earth sciences at the University of Delaware.
The study, published in the journal Nature Climate Change, is the first to demonstrate that wind farms, deployed on a grand scale, can buffer violent hurricanes, the researchers said.
The team simulated the impact from farms of tens of thousands of turbines, placed kilometres offshore and along the coast of cyclone-vulnerable cities.
"We found that when wind turbines are present, they slow down the outer rotation winds of a hurricane," said Mark Jacobson, a professor of civil and environmental engineering at Stanford University in California.
"This feeds back to decrease wave height, which reduces movement of air toward the centre of the hurricane, increasing the central pressure - which in turn slows the winds of the entire hurricane and dissipates it faster."
In the case of Hurricane Katrina, sustained peak wind speed would have been reduced by as much as 44 metres a second (158km/h).
The storm blew maximum gusts, but not sustained peaks, of about 282km/h, according to the National Oceanographic and Atmospheric Administration (NOAA), a US government agency.
Katrina's storm surge - waves whipped up by the exceptional winds - would have abated by up to 79 per cent, said the study.
In the case of Sandy, the model projected a drop of up to 140km/h in sustained peak wind speed and a 34-per-cent decrease in storm surge.