Suzana Camargo, executive director of the Initiative on Extreme Weather and Climate at Columbia University, said all the studies that examined Harvey's rainfall and climate change found a link, differing only in the percentage of the rain they attributed to climate change.
"You'd expect with a warmer atmosphere you can hold more water vapor so you'd have more rainfall, so it's not surprising that we can start seeing that in relation to hurricanes as well," she said. "That was one of the projections that we'd see by the end of the 21st century, but now in some specific hurricanes, we're starting to see it. The projections are for an increase on the order of 20% by the end of the century. But you see already that you can see the signal starting to appear in these storms."
Like a giant sponge, a hurricane absorbs water evaporating off the warm surface of the ocean. As the hurricane proceeds on its path, the sponge is constantly absorbing water and wringing itself out, producing rain. In a warmer climate, the sponge is bigger because warm air can hold more water vapor. And since the ocean itself would be warmer, more water would evaporate into the sponge to return to earth as rain.
With this warmer climate, other recent storms also set rainfall records. Last year Hurricane Florence set records in the Carolinas, with nearly 36 inches of rain, and Hurricane Lane set the Hawaii record with 52 inches.
Hurricane Maria struck Puerto Rico in late September 2017, and deluged the island with up to 38 inches of rain, triggering flash floods and landslides. A study in the journal Geophysical Research Letters found that because of climate change, the severe rainfall of Maria was nearly five times more likely to have taken place than it would have been in the 1950s.
"Our study concludes that extreme precipitation, like that of Hurricane Maria, has become much more likely in recent years and long-term trends in atmospheric and sea surface temperature are both linked to increased precipitation in Puerto Rico," the study said.
These heavy rains led inland flooding to exceed storm surge as a cause of hurricane deaths. From 1963 to 2012, storm surge caused 49% of hurricane deaths, with rain accounting for 27 percent, according to the National Hurricane Center. But in the past three years, storm surge accounted for just 4% of deaths.
Unlike storm surge, which affects only areas near the ocean, torrential rains can kill deep inland. The heaviest rain in Hurricane Florence fell over Elizabethtown, N.C., more than 50 miles from the ocean. The heaviest rain in Harvey fell on the town of Nederland, Texas, about 20 miles inland.
In Beaumont, just north of Nederland, a woman drowned after escaping from her car and being swept away. A minister and his wife tried to drive their pickup through a flooded intersection, got stuck and called 911. When rescuers arrived, they found their bodies in the submerged vehicle.
A family of six died after attempting to cross a flooded bridge in a van. The water picked up the van and carried it over to the adjacent bayou, where it started to sink. The driver escaped and yelled for the children in back to exit through the rear door, but they couldn't make it and were heard screaming as the van went under.