Weather Whiplash Brings Intense Rain, as Well As Drought
October 12, 2022
Above, team from Northwestern U looked at weather station data on rainfall over recent decades, and found what we all kind of knew. It’s raining harder.
This summer, several locations around the United States have experienced these wild, rapid swings from one weather extreme to another. About half of the country has undergone at least a moderate drought this summer. Parts of the West, the Midwest and Texas have experienced exceptional and historic drought conditions.
Then the storms came. On July 26 in St. Louis, a shocking 8.65 inches of rain fell to mark the city’s wettest day on record. The next day, in eastern Kentucky, rainfall rates topped 2 inches per hour and took the lives of 38 people. In August, eastern Illinois, Death Valley and Dallas also experienced significant or record-breaking rainfall. On Wednesday, flash flooding across central Mississippi swept away roads and prompted rescues.
“It is unusual, especially on the extreme precipitation [and] flash flood side,” said Daniel Swain, a climate scientist at the University of California at Los Angeles. “They’re not just beating a historical record by a marginal amount, but just completely blowing right past it and then some.”
Yet he isn’t surprised: A warmer climate is driving precipitation to higher extremes in both flooding and drought.
“The increase in both extreme precipitation events and in these wild swings between extreme precipitation and extreme aridity — this is how most people and most ecosystems on Earth are experiencing climate change,” Swain said.
Just like the old adage says: When it rains, it pours.
That turns out to be increasingly true for much of the United States, according to Northwestern University researchers.
In a new study, researchers compared observed rainfall from two climatologically distinct time periods and across 17 different climate regions in the U.S. They found that when it’s rained in recent decades, it’s rained more. In most regions, the intensity of the rainfall has shifted from lighter to more moderate and often heavy deluges.
When it rained east of the Rocky Mountains in recent decades, about 5% more precipitation fell. When it rained over the Pacific Coast or Rocky Mountains, however, no intensity changes were observed. Climate model simulations have previously predicted increases in precipitation intensity, particularly during extreme events, but the Northwestern study examined historically observed precipitation data across all intensities — and found a systematic shift in precipitation intensity in many parts of the country.
Washington Post, August 23, 2022:
What happened in the Dallas area came after the city and 29 percent of the state were gripped in a top-tier “exceptional” drought that impacted crops and drove water shortages. Some farmers were forced to thin their herds in a process called “culling,” according to the U.S. Drought Monitor. DFW International Airport was 11.11 inches behind for rainfall since Jan. 1.
Then Monday became the airport’s wettest calendar day on record.
The extreme rainfall in Dallas was a “1,000-year rain event,” an episode of flooding that has just a 0.1 percent probability of happening in any given year. It joins the company of 1,000-year rain events that struck Kentucky, St. Louis, eastern Illinois and Death Valley, Calif., since the end of July — all of which were experiencing abnormally dry conditions or in a severe drought beforehand.
Droughts can often make flooding worse. They kill plants and leave the ground bare, reducing soil absorption. They also harden top soils, which makes it easier for water to run off. The extremely dry ground, combined with the rapid rainfall, can trigger widespread flooding.
Kevin Trenberth spoke to me about this in 2015.
Climate Denial Crock of the Week 
October 12, 2022 at 5:20 pm
If it’s dry then it will be drier. If it’s wet it will be wetter. So much less near normal.