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. .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.Nineteen places doubled their previous number of days of extreme precipitation – from three a year to six.At the opposite extreme, eight states – including five in the West – had at least three record-dry years in the same time period.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 homes.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.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.
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.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. .
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.Bordering the Tennessee River, in the northwestern part of the state, Humphreys County sits in a region that has seen its annual precipitation rise by 1.6 inches in the past few decades.Joe Duncan recognized the weather was changing there – he said they get less snowfall and “more catastrophic weather” – so when he and his wife moved onto land next door to his mother last year, they studied a flood zone map.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. .The length of time between rain or snow storms 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.Rising temperatures mean the ingredients for storms may come together less often, so it doesn’t rain as frequently, said Russ Schumacher, an extreme rainfall researcher at Colorado State University and state climatologist for Colorado. .Even though California’s annual average rainfall isn’t changing that much, the state is experiencing “more rapid flip-flopping from extreme wet to extreme dry,” said Daniel McEvoy, assistant research professor at the Desert Research Institute at the Western Regional Climate Center.Due to intense atmospheric rivers bringing heavy rain in from the Pacific, the state shifted abruptly from a four-year drought to extreme wet in 2016 and 2017, McEvoy said.Two years ago near Chiefland, Florida, 62 inches of rain fell in less than three months on the Usher Land and Timber farm, just south of the state’s big bend, said Lynetta Usher Griner.
The next year, the sorghum was harvested five weeks late after 26.5 inches of rain fell in just four days.“We’re seeing these astronomically large rain events followed by long periods of lack of rainfall, and then we might have another flooding event,” she said. .Either extreme – flooding or extended dry periods – harms farm operations, causing costs to skyrocket, she said.“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.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. Though flooding may get less attention in the West, it’s still a big concern, especially in the mountains, said McEvoy, at the Desert Research Institute
When precipitation that used to fall as snow arrives as rain instead because it’s warmer, it can lead to additional flooding.
McEvoy said changes to the snowpack and increased runoff can further harm the region’s crucial water resources.Scientists don’t know the extent to which extreme downpours could increase, said Ken Kunkel, a research professor at North Carolina State University. A 4- to 5-degree increase in warming by 2100 could increase rainfall 15%-20%, Kunkel said
Higher emissions scenarios could increase temperatures another 8 to 10 degrees, and that could mean up to a 30% increase in extreme rainfall rates, he saidOnly a few places around the world aren’t forecast to get increases in precipitation, said Angeline Pendergrass, an assistant professor of atmospheric science at Cornell University. In the mainland United States, that includes only a small area in Southern California. That’s why the nation must shore up the infrastructure that wasn’t built for the increasing rain and storm events, experts saidPart 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“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 saidThe problems with the information FEMA uses to determine flood risk and the precipitation estimates by NOAA are similar, Moore and others saidChanging 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 beWhen the NOAA data for Texas was updated in 2018 from their earlier 1970s-era estimates, a 100-year storm had become a 25-year storm, said Chad Berginnis, executive director of the Association of Floodplain Managers. 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
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