Milwaukee Journal Sentinel
Extreme weather shows shift in rainfall
Heat changing moisture levels across country
Over eight days of wild weather in June, the realities of a changing climate grabbed the nation by its shoulders and shook.
In Michigan, a deluge dropped 7 inches of rain in Detroit, swamping highways and stranding cars.
At least 136 daily rainfall records were set during storms across five states along the Mississippi River.
Tropical Storm Claudette soaked a swath of the South, flooding homes in Louisiana and in Alabama, where it dropped up to 8 inches of rain and claimed 14 lives.
Meanwhile, the drought-stricken West grappled with soaring temperatures that shattered century-old records, prompted heat warnings and ultimately killed more than 200 people.
Wildfires exploded in Montana and scorched the earth in California.
Such events do occur naturally, but rarely have so many struck at once or to such an extreme degree, making it hard to ignore their connection to each other and to a warming world.
Rising temperatures and rising oceans have for years been framed as the impending disasters on the crest of climate change. But this year, like few before it, changing rainfall patterns bullied their way into the collective consciousness.
USA TODAY reporters analyzed more than a century of precipitation records from the National Oceanic and Atmospheric Administration and a unique collection of snow and rain extremes computed by Alaska-based climate researcher Brian Brettschneider.
Reporters read thousands of pages of climate assessments, scientific papers, weather reports and government documents. They interviewed more than 70 people, including climate scientists, academic researchers, local and federal officials, and residents forced from their homes by drought and flood.
Taken together, the reporting reveals a stunning shift in the way precipitation falls in America.
Heat has changed how moisture moves across the country. Scientists say it alters the flow of the jet stream, extends droughts, and increases evaporation from land and from bodies of water, including the Atlantic and Pacific oceans, the Great Lakes and the Gulf of Mexico.
East of the Rockies, more rain is falling and it’s coming in more intense bursts. In the West, people are waiting longer to see any rain at all.
Readings from hundreds of rain gauges across the continental U.S. tracked for more than 100 years reveal a noticeable inflection point before the turn of the 21st century.
Of 285 weather stations, 44% get at least one more top rainfall event per year now than they did three decades ago, based on data compiled by Brettschneider. That means what used to count as the top three wettest rainfalls of the year now happen at least four times a year.
Nineteen places doubled their previous number of days of extreme precipitation – from three a year to six.
As deluges grow in frequency and severity, annual precipitation has increased for more than half the nation. At some point over the past three years, 27 states – all east of the Rocky Mountains – experienced their highest 30-year average since record keeping began in 1895, according to a USA TODAY analysis of NOAA data.
A dozen states, including Iowa, Ohio and Rhode Island, saw five of their 10 wettest years in history over the past two decades.
At the opposite extreme, eight states – including five in the West – had at least three record-dry years in the same time period. That’s double what would be expected based on historical patterns.
As states rack up records for rainfall, flooding, droughts and wildfire, it’s becoming clear our country was built for the climate of the past.
Roads, bridges, sewer systems and entire communities that decades ago seemed safe from fire and flood now lie within one or both danger zones.
An October report by the nonprofit First Street Foundation warned that one-fourth of the nation’s “critical infrastructure,” including roads, utilities, airports and emergency services, now faces flood risk from rainfall and sea level rise, as do 1 in 7 residential properties – about 12.4 million.
Heat, lack of humidity, and wind are combining more frequently to enhance the risk of wildfire. Climate Central, a nonprofit research organization, looked at 17 Western states and found parts of New Mexico now have at least 60 additional days when the fire risk is more extreme than 50 years ago.
Parts of 11 other states, including Arizona, California, Colorado, Oregon and Texas, saw more than a 100% increase in these “fire weather days.”
These calamities displace families, claim lives and leave officials from coast to coast conflicted over which crisis to plan for next and how to pay for it all.
NOAA reported at least 133 “billiondollar disasters” in the decade ending in 2020, double the previous decade, at a cost of more than $867 billion. Meanwhile, the annual average number of flood claims paid by FEMA also doubled between 1997 and 2020, to 52,000.
Scientists say it’s too late to stave off some of the climate change-driven precipitation extremes we’re experiencing today. But the nation could take steps to reduce greenhouse gas emissions that amplify the weather extremes and take more aggressive measures to reduce flood risk.
Given the increasing frequency of weather disasters, “one would think the nation might be galvanized to action,” said Rob Moore, a senior policy analyst with the Natural Resources Defense Council. “And yet we are not incorporating what we know about the future into our decisions about what we build, where we build and how we build as a nation.”
What’s causing it?
The earth has always produced erratic weather patterns. But now the heaviest downpours and droughts are growing more extreme. That trend started in the late 20th century, as the accumulation of greenhouse gases like carbon dioxide and methane reached critical levels in the atmosphere.
Climate scientists said these gases trap more of the energy radiating from the planet’s surface, causing the earth to warm.
This warming doesn’t just raise temperatures. It intensifies how water cycles between earth and sky.
Heat hastens evaporation. It draws more water into the air where it gathers into systems that can form wetter storms. For every 1.8 degrees Fahrenheit of warming, 7% more moisture is absorbed, said David Easterling, director of NOAA’S National Climate Assessment Technical Support Unit.
It’s one of the reasons behind many of this summer’s rainiest storms, including Hurricanes Henri and Ida, that flooded communities throughout the South and Northeast this August.
For these storms and others throughout the year, much of their moisture comes from the Gulf of Mexico, Great Lakes and Atlantic Ocean.
Gulf waters alone have warmed about 1.3 degrees over the past four decades.
A warmer Gulf contributes to more rainfall in hurricanes and tropical storms, but its moisture also helps form wetter storms as far north as Wisconsin, Easterling said.
At the same time, some scientists said rising temperatures have altered the summertime movement of the jet stream that transports moisture across the country. Weather systems that used to hustle along get stalled more often now, dumping more rain in one place.
Instead of flowing quickly across the north, the jet stream moves slower and gets bigger, wavy dips that trap high and low pressure systems in place, said Michael Mann, a climatologist at Penn State University and author of the book “The New Climate War.”
The trapped highs and lows in the summertime affect the weather across the country, Mann said. For example, they can produce extreme heat, drought and wildfires in the West and drop huge amounts of rain to the east at the same time.
Scientists can’t say for sure how much of the rain in each storm is directly attributed to the changing climate, Brettschneider said, but the shifts become apparent when comparing a sampling of current and older events.
More intense rains
Climate change also has been blamed for fueling the intensity of the storms that unleashed record rainfall and sparked deadly flooding across Tennessee in August.
The day that storm hit started like just another rainy morning in Humphreys County.
Weather forecasters had issued flash flood advisories, warning of 2-4 inches of rain, but no one had predicted four times that much or the catastrophe it would bring.
Typical summer thunderstorms sweep through at 50-60 mph. But on Aug. 21, a system got caught up with a stalled front and traveled through at only 10-15 mph. Meeting up with a pool of Gulf moisture overhead, it forced storms to rain over the area again and again, dropping more than 12 inches of rain in seven hours in the small city of McEwen.
The total rainfall – 17 inches – broke the state’s all-time record and triggered deadly flooding in Waverly.
Around 7 a.m., Joe Duncan looked outside and saw water rushing through his yard. He gathered his wife, daughter and two grandchildren and headed out through knee-high water to pick up his mother so they could evacuate. When they reached her house, Duncan turned around just in time to see his mobile home tilt sideways.
By this time, 9 inches of rain had fallen in six hours, sending Trace Creek out of its banks and raging toward Waverly in a muddy torrent.
Calls started lighting up the
Humphreys County 911 Center.
The debris-filled Trace Creek hurtled toward a pair of bridges east of Waverly – one for U.S. 70 and one for the railroad. Mayor Buddy Frazier and others believe debris lodged at the bridges, creating a temporary dam until the water crashed through and sent a “tsunami” into Waverly.
Duncan’s home slammed against a tree and split into three pieces. He said the nearby home built in the early 1900s also was destroyed.
Twenty people died in the disaster. They’re among 144 flood-related deaths in the nation this year, the second-highest since 1985.
Rising temperatures also lengthen dry spells, creating wild swings between downpours and droughts.
The length of time between rain increased by three days on average across the West from 1976 to 2019, according to research published this year by scientists with the U.S. Department of Agriculture and the University of Arizona.
The researchers also found the longest interval between rains each year increased by 11 days in the West, to 32 days across the region. In the desert Southwest, it increased by 17 days to 48 days.
More dry days and drought
While increasingly intense rains fall east of the Rockies, the West experiences intense drought. Rising temperatures and lingering high pressure systems zap greater moisture from soils and plants.
“With precipitation you’re only getting half of the picture,” said Daniel Swain, a climate scientist at UCLA and the National Center for Atmospheric Research. “When it comes to drought, temperature is increasingly important, and temperatures are rising a lot.”
Together, the intense heat and longer intervals between rains contribute to the conditions creating more recordbreaking wildfires in the West.
All but two of California’s 20 largest wildfires in history have happened since 2003.
Oregon had one of its most destructive wildfire seasons on record last year with roughly 2,200 fires that burned more than 1.1 million acres and destroyed more than 4,000 homes.
One of those homes belonged to the Flores family, who lived in the Coleman Creek Estates mobile home park near Medford in the southern part of the state.
Seventeen years old at the time, Julio Bryan Flores woke up the morning of Sept. 8, 2020, looking forward to celebrating his mother’s birthday when a neighbor’s call alerted the family to danger, he said.
Soon ash fell from the sky. The entire neighborhood evacuated. Bryan’s father, who had been away, returned home just in time to get the dog, but not his mechanics tools.
“We could see fires literally starting everywhere,” Bryan said. “We were surrounded by them.”
The family escaped, but the fire destroyed their home and possessions. When Bryan and his dad returned a week after the fire, “it was a nightmare.”
“There were just the colors white and black everywhere, burned bicycles, destroyed cars, toys left on the street, just burned,” Bryan said.
Once an intense wildfire burns through an area, it leaves the soil hardened and scarred and weakens its ability to absorb water. So when the rains come, they turn dry creek beds into raging rivers, like the one that swept up a Prius near Flagstaff, Arizona, in August and carried it down the street in a viral video.
The atmospheric river that swept across the West in late October dropped anywhere from 3 to 13 inches of rain across California, Oregon and Nevada.
Action needed now
Critical steps are needed – and soon – to try to keep downpours from growing ever more intense, correct past mistakes and adapt our surroundings to the new reality, experts said.
Many call for sweeping changes to curtail warming, upgrade stormwater and utility systems, and revamp federal guidelines and standards and stop building in vulnerable places.
“The future is still in our hands,” said Mann.
Two things appear to be true for “pretty much everywhere that’s populated and on land,” Swain said. “Everyone is getting warmer and everyone is seeing, or should see shortly, more intense precipitation events.”
Part of the problem is the nation’s woefully outdated federal precipitation estimates and inadequate flood zone mapping, said Moore of the Natural Resources Defense Council. Neither takes into account recent rainfall increases, much less future projections.
“We’re still designing highways and stormwater systems and siting people’s homes without any consideration of what the weather is going to look like in 30, 40 or 50 years,” Moore said.
Changing rainfall amounts and rising sea levels mean the estimates, such as a 1-in-100 year flood or a 1-in-25 year rainfall, just aren’t the same as they used to be.
The NOAA estimates guide governments, engineers and others when designing infrastructure. A new generation of estimates, called Atlas 14, began in 2002, but has never been completed for the entire country.
One study showed that for Michigan, Wisconsin, Iowa and Minnesota, the historic estimate of a 1-in-100-year storm is now a 1-in-40-year storm, said Daniel Wright, an assistant professor of civil and environmental engineering at University of Wisconsin-Madison. “These sorts of storms are happening 21⁄2 times as often as they should be.”
Labeling storms as a once-in-a-generation occurrence gives people the impression they can’t have another, said Peter Schultz, vice president of climate adaptation and resilience for ICF, an international climate change consulting firm.
But that’s not accurate.
“If you have dice and you roll a three, that doesn’t mean the next time you roll the dice you can’t get a three, you absolutely can,” he said. “Nature is still rolling the dice, but it’s not fair dice anymore, it’s dice that are coming out toward those higher numbers.”
“With precipitation you’re only getting half of the picture. When it comes to drought, temperature is increasingly important, and temperatures are rising a lot.” Daniel Swain Climate scientist at UCLA and the National Center for Atmospheric Research