by Kit Stolz [published in the Ventura County Reporter April 14, 2022]
Ventura County is warming faster than any other county in the continental United States, according to data compiled by the National Oceanographic and Atmospheric Administration (1). The county has warmed 4.75 degrees Fahrenheit since 1895, which is about a half a degree warmer than either Los Angeles or Santa Barbara counties, and one degree hotter than the global average of warming that will be catastrophic around the world, according to climate scientists.
To meet the challenge of the increasingly hot climate, and to keep residents up to date about the risks from Santa Ana winds, heat waves, wildfires, storms and debris flows, meteorologists at the National Weather Service station in Oxnard have taken advantage of advances in forecasting technology as well as increased use of social media to better alert and inform the public.
Meteorologists believe that high-resolution modeling of storms has enabled them to continue to forecast the weather accurately, but they worry about their ability to effectively “message” the risk of climate extremes to a public weary of catastrophic firestorms, heat waves and downpours.
GOING TO EXTREMES
Mark Jackson, the meteorologist in charge of the Oxnard station, points out that the increase in warming in the county, from an annual average of about 72 degrees in the 19th century to over 76 degrees in the 21st century, doesn’t really tell the story.
“The reason that number is alarming is not the difference between an average of 72 degrees and of 76 degrees,” Jackson said. “The shift in that mean value means that you have increased the probability of extreme temperatures that cause the greatest impact.”
Jackson added that extremes as a general rule are a greater challenge for forecasters. Climate change by its nature pushes weather towards the extremes.
“Climate change is kind of like a silent killer,” said Jackson. “The beauty of a storm is that we see it, we witness it, and it’s right there. We can’t see climate change as directly. Fortunately our forecasting technology has kept pace with climate change and we’re better prepared. From a statistical standpoint our seven-day forecasts are as accurate now as our five-day forecasts were a few years ago. This allows us to give our overall message to the public and our public safety partner agencies earlier, but we still are limited in our ability to forecast the extremes.”
The Montecito mudslide of Jan. 9, 2018, killed 21 people and continues to be the largest known post-fire debris flow in California history. Three days before, on Jan. 6, Jackson and his colleagues could see on their screens a narrow band of extreme rain heading toward the ridge overlooking Montecito and nearby coastal cities.
“With debris flows it’s all about high-intensity, short-duration rainfall, and as we were marching closer to the time of the event, we were seeing more and more intense rainfall. Our high-resolution physical models go out 36 or 48 hours or so, and as the event gets closer, we’re jumping up and down and screaming louder,” said Jackson, whose Oxnard station serves four Southern California counties, from San Luis Obispo to Los Angeles.
“This was a perfect storm in terms of making a debris flow possible,” added Jackson. “This was falling on a burn area that had never been rained on before, from the Thomas Fire that was still not contained. When we were about 45 minutes away from the event early that Tuesday morning, we knew there was going to be a debris flow but we just didn’t know exactly where.”
Eric Boldt, a forecaster who has worked closely with Jackson at the Oxnard station, pointed out in a joint interview that the National Weather Service and a team of public safety officials from Santa Barbara County gave an outdoor press conference in the area on the Friday before the event, warning of the possibility of extreme rain and and then again on Monday, warning of the likelihood of an extreme rain and debris flows, and asking residents to prepare to evacuate.
“On Monday we announced that this would be an extreme event, with rates of 2-4 inches of rain an hour. These are really bad rates,” Boldt said. “For us as meteorologists, we’re thinking, ‘holy cow, that’s crazy.’”
Although the meteorologists accurately forecast the time and duration of the rainfall event, and warned of its seriousness and prepared residents to evacuate, they could not foresee exactly how hard the rain would fall, or exactly where. And the intensity of the rainfall exceeded their most extreme estimates.
“We still have limitations on our ability to predict that kind of extreme event,” Jackson said. “We may have reached a ceiling — I doubt we will ever be able to accurately forecast an event that produces five or more inches of rain an hour. In Montecito we had a half inch of rain in five minutes at one point.”
Jackson and his team of meteorologists were well aware of the danger, but could not convince most of the public at risk to evacuate despite their warnings.
“It was very frustrating because what else could we have done?” Jackson said. “We had prepared and we had prepared our agency partners. Santa Barbara County had issued their very first non-fire evacuation order ever, but it wasn’t enough. Why wasn’t every person in that Santa Barbara front country away from their house? We try to make sure people understand that they can’t wait for the debris flow to happen before they respond, because it’ll be too late, debris flows are too fast.”
A post-disaster report from the California Geological Survey(2) found that the debris flows in Montecito in January of 2018 moved about 1.5 million cubic meters of earth at a rate of 10-15 miles an hour. The debris flows were as much as 25-30 feet deep, and carried boulders as large as a truck. In one night they destroyed 100 houses and damaged 300 more, killed 21 people, and buried a section of Highway 101 in debris. Two people are still missing in the aftermath.
“Could we have even imagined half the mountain coming down on Montecito?” asked Jackson. “No, because we’ve never seen anything like that happen before.”
INCREASED FREQUENCY OF “ONE-TWO PUNCH”
But many more such climate-fueled events are coming to western states,
according to a new study co-led by Samantha Stevenson(3), a climatologist at the Bren School at the University of California, Santa Barbara, which found “compound events” such as those seen in Montecito — a firestorm followed in short order by a torrential downpour — will become increasingly frequent this century in California and the west. The modeling study showed that the frequency of such “compound events” will increase by 100 percent this century in California, and by up to 700 percent in the Pacific Northwest.
“Yes, unfortunately, this type of one-two punch — as we’ve been calling compound events — will become more frequent this century,” Stevenson said. “I can’t predict how often this will happen, because that will depend on our future climate choices, and also on how many ignitions happen during those conditions, but they will become more frequent.”
Stevenson herself had not been at UCSB for long before the Montecito catastrophe, and was shocked by what she saw. It motivated her to look at the risks of “compound events.”
“I’m a relatively recent transplant,” she said. “I arrived in the fall of 2017, just two months before the Thomas Fire. I thought I knew something about wildfire from living in Colorado, but after that happened — oh my God. California wildfires are a whole different animal.”
A co-author on Stevenson’s paper, climatologist Daniel Swain of UCLA’s Institute of the Environment and Sustainability as well as the National Center for Atmospheric Research, has been warning for years that climate change will mean increasingly extreme weather and “climate whiplash” in California, in which hot, parched lands will be abruptly hit with torrential downpours, just as happened in Montecito after the Thomas Fire.
Part of that increased risk comes from a greater likelihood of drought. Another recent study from Stevenson’s team (4) shows that the drying out of the soil has outpaced the variability of rainfall in many places in the West, including Ventura County. This means that the county and Southern California have been drying out since the 1990s, despite occasional years of above-average rainfall, and have little chance of returning to a “normal” pattern of average rainfall from the past.
Stevenson said that megadrought — a drought that lasts 20 years or more — must now be considered “normal” for Southern California.
“If we reach a stable concentration of CO2 in the atmosphere, then at some point we’ll stabilize, but the models are saying that we’re not there yet,” Stevenson said. “In a world where we are continuously increasing our greenhouse gas concentrations, that drying trend in the West will persist throughout the 21st century.”
“WE’RE CHANGING THE NORMALS”
When it comes to measuring what is “normal” in our climate, Boldt noted that every 10 years the “normals” are updated by NOAA, and that since the most recent update (which covers the period of 1991-2020, versus the old “normals” of 1981-2010) California as a whole has warmed one degree at night and one to two degrees during the day.
“These are rapid changes — in only 30 years, we’re changing the normals, to be warmer and drier,” Boldt said. “What we’re seeing in this new century is that time after time, we’re breaking records. We’re routinely breaking records that have stood for 80-100 years, and sometimes the new records we’re setting are for all-time highs.”
Another occurred in the first week in April, in which a heat wave set all-time records in county locations. Another drought record occurred in January and February this year, when California set an all-time low for rainfall for those winter months. State climatologist Michael Anderson in Sacramento said that he expected precipitation to drop off after a very wet December, but he couldn’t estimate the change.
“I had a feeling it would become drier, but not to this degree,” he said. “That’s the challenge. Will it be drier? Will it be extremely dry? Or will it be record-setting dry? I’m trying to get that sorted out.”
The forecasters in Oxnard face a similar challenge. They suspect a ridge of high pressure in the North Pacific, known among forecasters as the “Ridiculously Resilient Ridge,” is making it difficult for storms from the Gulf of Alaska to slide down the coast to California as in the past, while also encouraging Santa Ana wind conditions. But at the same time, they didn’t think that the rain would vanish in what typically has been the two wettest months of the year.
“In December in some areas we had three times the normal precipitation,” Jackson said. “We joked about it and said — now watch the spigot get turned off. Maybe we shouldn’t have joked about it.”
- “2°C: Beyond the Limit: Extreme climate change has arrived in America,” Steven Mufson, Chris Mooney , Juliet Eilperin and John Muyskens, Washington Post, Aug. 13, 2019.
- “Post-Fire Debris Flow Facts,” California Geological Survey, Department of Conservation.
- “Climate change increases risk of extreme rainfall following wildfire in the western United States,” Danielle Touma, Samantha Stevenson, Daniel L. Swait et al, Science Advances, Vol. 8, No. 13, April 1, 2022.
- “Twenty-first century hydroclimate: A continually changing baseline, with more frequent extremes,” Samantha Stevenson, Sloan Coats, Danielle Touma et al, Proceedings of the National Academy of Sciences of the United States of America, March 14, 2022.
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