Human-caused global heating accounts for more than 40 percent of the megadrought ravaging the southwestern United States
(AFP/Raul ARBOLEDA)
Marlowe HOOD
Mon, February 14, 2022,
The megadrought that has parched southwestern United States and parts of Mexico over the last two decades is the worst to hit the region in at least 1,200 years, researchers said Monday.
Human-caused global heating accounts for more than 40 percent of the dry spell's intensity, they reported in the journal Nature Climate Change.
"The turn-of-the-21st-century drought would not be on a megadrought trajectory without anthropogenic climate change," lead author Park Williams, an associate professor at the University of California in Los Angeles, and colleagues wrote.
Over the last decade, California and other western states have experienced severe water shortages, triggering periodic restrictions on water usage and forcing some communities to import bottled water for drinking.
Marlowe HOOD
Mon, February 14, 2022,
The megadrought that has parched southwestern United States and parts of Mexico over the last two decades is the worst to hit the region in at least 1,200 years, researchers said Monday.
Human-caused global heating accounts for more than 40 percent of the dry spell's intensity, they reported in the journal Nature Climate Change.
"The turn-of-the-21st-century drought would not be on a megadrought trajectory without anthropogenic climate change," lead author Park Williams, an associate professor at the University of California in Los Angeles, and colleagues wrote.
Over the last decade, California and other western states have experienced severe water shortages, triggering periodic restrictions on water usage and forcing some communities to import bottled water for drinking.
Occasional heavy snow or rainfall have not been enough to compensate.
2021 was especially dry. As of February 10, 95 percent of western US had drought conditions, according to the US government's Drought Monitor.
Last summer, two of North America's largest reservoirs -- Lake Mead and Lake Powell -- reached their lowest recorded level in more than a century.
The odds are high that the current dry spell will continue for at least a couple of years, probably longer, according to the findings.
Running simulations based on soil moisture records stretching back 1,200 years, the researchers calculated a 94 percent chance that the drought would extend through 2022.
There's a three-in-four chance it will run until the end of decade.
Tree-ring analysis shows that the area west of the Rocky Mountains from southern Montana to northern Mexico was hit repeatedly by so-called megadroughts -- lasting at least 19 years -- between the years 800 and 1600.
- Chronic water scarcity -
Earlier research had established that the period 2000-2018 was likely the second worst drought since the year 800, topped by one in the late 1500s.
Data from 2019-2021, backed by new climate models released last year, have revealed the current drought to be worse than any from the Middle Ages.
But without climate change it "wouldn't hold a candle to the megadroughts of the 1500s, 1200s or 1100s," Williams said in a statement.
Western North America is not the only region hit by increasingly severe dry periods.
Climate change worsened the El Nino-driven droughts of 2015-2016, leading to widespread crop failures, loss of livestock, Rift Valley fever outbreaks, and increased rates of malnutrition.
Globally, 800 million to three billion people are projected to experience chronic water scarcity due to drought caused by two degrees Celsius warming above preindustrial levels, according to a draft 4,000-page Intergovernmental Panel on Climate Change (IPCC) report on climate impacts seen by AFP.
In a 4C world, that figure is up to four billion people.
Earth's surface has already warmed 1.1C on average, and is almost certain to breach the 1.5C cap called for in the Paris Agreement within two decades.
Other natural extreme weather events enhanced by global warming include deadly heatwaves, flood-causing rainfall and superstorms.
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West megadrought worsens to driest in at least 1,200 years
By SETH BORENSTEIN
Water drips from a faucet near boat docks sitting on dry land at the Browns Ravine Cove area of drought-stricken Folsom Lake in Folsom, Calif., on May 22, 2022. The American West's megadrought deepened so much last year that it is now the driest it has been in at least 1200 years and a worst-case scenario playing out live, a new study finds. (AP Photo/Josh Edelson, File)
The American West’s megadrought deepened so much last year that it is now the driest in at least 1,200 years and is a worst-case climate change scenario playing out live, a new study finds.
A dramatic drying in 2021 — about as dry as 2002 and one of the driest years ever recorded for the region — pushed the 22-year drought passed the previous record-holder for megadroughts in the late 1500s and shows no signs of easing in the near future, according to a study Monday in the journal Nature Climate Change.
The study calculated that 42% of this megadrought can be attributed to human-caused climate change.
“Climate change is changing the baseline conditions toward a drier, gradually drier state in the West and that means the worst-case scenario keeps getting worse,” said study lead author Park Williams, a climate hydrologist at UCLA. “This is right in line with what people were thinking of in the 1900s as a worst-case scenario. But today I think we need to be even preparing for conditions in the future that are far worse than this.”
Williams studied soil moisture levels in the West — a box that includes California, Wyoming, Utah, Nevada, Arizona, most of Oregon and Idaho, much of New Mexico, western Colorado, northern Mexico, and the southwest corners of Montana and Texas — using modern measurements and tree rings for estimates that go back to the year 800. That’s about as far back as estimates can reliably go with tree rings.
A few years ago, Williams studied the current drought and said it qualified as a lengthy and deep “megadrought” and that the only worse one was in the 1500s. He figured the current drought wouldn’t surpass that one because megadroughts tended to peter out after 20 years. And, he said, 2019 was a wet year so it looked like the western drought might be coming to an end.
But the region dried up in late 2020 and 2021.
All of California was considered in official drought from mid-May until the end of 2021, and at least three-quarters of the state was at the highest two drought levels from June through Christmas, according to the U.S. drought monitor.
“For this drought to have just cranked up back to maximum drought intensity in late 2020 through 2021 is a quite emphatic statement by this 2000s drought saying that we’re nowhere close to the end,” Williams said. This drought is now 5% drier than the old record from the 1500s, he said.
The drought monitor says 55% of the U.S. West is in drought with 13% experiencing the two highest drought levels.
This megadrought really kicked off in 2002 — one of the driest years ever, based on humidity and tree rings, Williams said.
“I was wondering if we’d ever see a year like 2002 again in my life and in fact, we saw it 20 years later, within the same drought,” Williams said. The drought levels in 2002 and 2021 were a statistical tie, though still behind 1580 for the worst single year.
Climate change from the burning of fossil fuels is bringing hotter temperatures and increasing evaporation in the air, scientists say.
Williams used 29 models to create a hypothetical world with no human-caused warming then compared it to what happened in real life — the scientifically accepted way to check if an extreme weather event is due to climate change. He found that 42% of the drought conditions are directly from human-caused warming. Without climate change, he said, the megadrought would have ended early on because 2005 and 2006 would have been wet enough to break it.
The study “is an important wake-up call,” said Jonathan Overpeck, dean of environment at the University of Michigan, who wasn’t part of the study. “Climate change is literally baking the water supply and forests of the Southwest, and it could get a whole lot worse if we don’t halt climate change soon.”
Williams said there is a direct link between drought and heat and the increased wildfires that have been devastating the West for years. Fires need dry fuel that drought and heat promote.
Eventually, this megadrought will end by sheer luck of a few good rainy years, Williams said. But then another one will start.
Daniel Swain, a UCLA climate scientist who wasn’t involved in the study, said climate change is likely to make megadrought “a permanent feature of the climate of the Colorado River watershed during the 21st century.”
A car crosses Enterprise Bridge over Lake Oroville's dry banks on May 23, 2021, in Oroville, Calif. The American West's megadrought deepened so much last year that it is now the driest it has been in at least 1200 years and a worst-case scenario playing out live, a new study finds. (AP Photo/Noah Berger, File)
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Read more of AP’s climate coverage at http://www.apnews.com/Climate
___
Follow Seth Borenstein on Twitter at @borenbears.
By SETH BORENSTEIN
Water drips from a faucet near boat docks sitting on dry land at the Browns Ravine Cove area of drought-stricken Folsom Lake in Folsom, Calif., on May 22, 2022. The American West's megadrought deepened so much last year that it is now the driest it has been in at least 1200 years and a worst-case scenario playing out live, a new study finds. (AP Photo/Josh Edelson, File)
The American West’s megadrought deepened so much last year that it is now the driest in at least 1,200 years and is a worst-case climate change scenario playing out live, a new study finds.
A dramatic drying in 2021 — about as dry as 2002 and one of the driest years ever recorded for the region — pushed the 22-year drought passed the previous record-holder for megadroughts in the late 1500s and shows no signs of easing in the near future, according to a study Monday in the journal Nature Climate Change.
The study calculated that 42% of this megadrought can be attributed to human-caused climate change.
“Climate change is changing the baseline conditions toward a drier, gradually drier state in the West and that means the worst-case scenario keeps getting worse,” said study lead author Park Williams, a climate hydrologist at UCLA. “This is right in line with what people were thinking of in the 1900s as a worst-case scenario. But today I think we need to be even preparing for conditions in the future that are far worse than this.”
Williams studied soil moisture levels in the West — a box that includes California, Wyoming, Utah, Nevada, Arizona, most of Oregon and Idaho, much of New Mexico, western Colorado, northern Mexico, and the southwest corners of Montana and Texas — using modern measurements and tree rings for estimates that go back to the year 800. That’s about as far back as estimates can reliably go with tree rings.
A few years ago, Williams studied the current drought and said it qualified as a lengthy and deep “megadrought” and that the only worse one was in the 1500s. He figured the current drought wouldn’t surpass that one because megadroughts tended to peter out after 20 years. And, he said, 2019 was a wet year so it looked like the western drought might be coming to an end.
But the region dried up in late 2020 and 2021.
All of California was considered in official drought from mid-May until the end of 2021, and at least three-quarters of the state was at the highest two drought levels from June through Christmas, according to the U.S. drought monitor.
“For this drought to have just cranked up back to maximum drought intensity in late 2020 through 2021 is a quite emphatic statement by this 2000s drought saying that we’re nowhere close to the end,” Williams said. This drought is now 5% drier than the old record from the 1500s, he said.
The drought monitor says 55% of the U.S. West is in drought with 13% experiencing the two highest drought levels.
This megadrought really kicked off in 2002 — one of the driest years ever, based on humidity and tree rings, Williams said.
“I was wondering if we’d ever see a year like 2002 again in my life and in fact, we saw it 20 years later, within the same drought,” Williams said. The drought levels in 2002 and 2021 were a statistical tie, though still behind 1580 for the worst single year.
Climate change from the burning of fossil fuels is bringing hotter temperatures and increasing evaporation in the air, scientists say.
Williams used 29 models to create a hypothetical world with no human-caused warming then compared it to what happened in real life — the scientifically accepted way to check if an extreme weather event is due to climate change. He found that 42% of the drought conditions are directly from human-caused warming. Without climate change, he said, the megadrought would have ended early on because 2005 and 2006 would have been wet enough to break it.
The study “is an important wake-up call,” said Jonathan Overpeck, dean of environment at the University of Michigan, who wasn’t part of the study. “Climate change is literally baking the water supply and forests of the Southwest, and it could get a whole lot worse if we don’t halt climate change soon.”
Williams said there is a direct link between drought and heat and the increased wildfires that have been devastating the West for years. Fires need dry fuel that drought and heat promote.
Eventually, this megadrought will end by sheer luck of a few good rainy years, Williams said. But then another one will start.
Daniel Swain, a UCLA climate scientist who wasn’t involved in the study, said climate change is likely to make megadrought “a permanent feature of the climate of the Colorado River watershed during the 21st century.”
A car crosses Enterprise Bridge over Lake Oroville's dry banks on May 23, 2021, in Oroville, Calif. The American West's megadrought deepened so much last year that it is now the driest it has been in at least 1200 years and a worst-case scenario playing out live, a new study finds. (AP Photo/Noah Berger, File)
___
Read more of AP’s climate coverage at http://www.apnews.com/Climate
___
Follow Seth Borenstein on Twitter at @borenbears.
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