MIAMI-The rain started even before Hurricane Harvey made its way across the Gulf of Mexico and settled atop Texas. It kept coming, overflowing curbs, climbing up staircases, trapping people on roofs and makeshift rafts and drowning dozens.
The record-breaking 60 inches of rain forced forecasters to add new colors to graphics measuring rainfall.
New research suggests storms of the future may look more and more like Harvey, higher category hurricanes supercharged by warming ocean waters with drenching rains. For communities also facing the threat of sea level rise, it means more of an enemy they're already battling-water.
A recent study led by scientists at the National Center for Atmospheric Research backed up what some researchers have long suspected about hurricanes of the future: climate change will make storms stronger, slower and much rainier.
Researchers used a super computer to simulate the named storms that formed between 2000 and 2013 in a world 9 degrees warmer-the predicted heat increase by the end of the century as burning fossils fuels create a "greenhouse gas" effect and trap heat in the atmosphere. That heat is largely absorbed by the seas, which raises the water temperature and makes the air above it more humid.
"Hurricanes build off the warm water," said Ethan Gutmann, a project scientist with NCAR. "If you increase the amount of moisture coming off of the ocean and the temperature of the air itself you're really driving this entire heat engine and putting gas into the car."
Other research estimates that a warming world has already made a storm as wet as Hurricane Harvey more likely to occur in 2018 than it would have been at the end of last century. Since then, that kind of hurricane went from a one in a hundred year storm to a once in 16 years event.
It took a "large fraction" of the super computer about a year to spit out the findings for the new study. None of the past hurricanes that were simulated hit Harvey levels of record-breaking rain, and not every single storm reacted the same way, but some storms jumped up categories and researchers saw an average of about a 25 percent increase in rainfall.
The team didn't look at how these future conditions would affect the creation of hurricanes, only how they'd have changed past storms. Scientists generally believe that climate change won't cause extra storms. If anything, there might be slightly fewer.
But the new study supported a line of research that the hurricanes of the future will likely be stronger. Gutmann said his research suggests there will be relatively more Category 3, 4 and 5 storms and fewer Category 1 and 2 storms.
That's just one more stress for drainage-challenged South Florida as the region battles another symptom of climate change-sea level rise. By 2100, the world simulated in the hurricane study, South Florida is predicted to see between 3 and 5 feet of sea rise, according to a projection by the Southeast Florida Climate Compact. With just 3 feet of sea rise, nearly half a million people and $145 billion of property are at risk in Florida alone, according to Climate Central.
"That's the background, It amplifies all other things and complicates them," said James Murley, the chief resiliency officer for Miami-Dade County. His office is charged with helping the region adapt to the climate of the future, stronger hurricanes included.
South Florida, with sea level rise pushing up groundwater and leaving little room for storm surge and rain from these storms to drain, would likely face worse flooding with these hurricanes.
"As the water level continues to rise we'll have more water behind those storm surge events," said Tiffany Troxler, director of science for Florida International University's Sea Level Rise Solutions Center. "That translates into more powerful storm surge events."
Many of the region's plans-devised by municipal resiliency offices or in conjunction with outside groups like 100 Resilient Cities-to become more resilient to sea level rise, like elevated roads, pumps and plants designed to absorb water, will also help combat heavy rainfall from hurricanes.
Fighting storm surge will take strategies like sea walls and planting mangroves along the coast, which break up wave energy and slow beach erosion, Troxler said.
"It will require sort of an additive approach in order to accommodate the effects of storm surge," she said.
This upcoming hurricane season is expected to be active but normal, with one to four major hurricanes.