Climate-Driven #Megadrought Is Emerging in Western U.S., Says Study — Columbia University

Here’s the release from Columbia University (Kevin Krajik):

With the western United States and northern Mexico suffering an ever-lengthening string of dry years starting in 2000, scientists have been warning for some time that climate change may be pushing the region toward an extreme long-term drought worse than any in recorded history. A new study says the time has arrived: a megadrought as bad or worse than anything even from known prehistory is very likely in progress, and warming climate is playing a key role. The study, based on modern weather observations, 1,200 years of tree-ring data and dozens of climate models, appears this week in the leading journal Science.

“Earlier studies were largely model projections of the future,” said lead author Park Williams, a bioclimatologist at Columbia University’s Lamont-Doherty Earth Observatory. “We’re no longer looking at projections, but at where we are now. We now have enough observations of current drought and tree-ring records of past drought to say that we’re on the same trajectory as the worst prehistoric droughts.”

Reliable modern observations date only to about 1900, but tree rings have allowed scientists to infer yearly soil moisture for centuries before humans began influencing climate. Among other things, previous research has tied catastrophic naturally driven droughts recorded in tree rings to upheavals among indigenous Medieval-era civilizations in the Southwest. The new study is the most up-to-date and comprehensive long-term analysis. It covers an area stretching across nine U.S. states from Oregon and Montana down through California and New Mexico, and part of northern Mexico.

Areas of southwestern North America affected by drought in the early 2000s; darker colors are more intense. Yellow box shows the study area. (Adapted from Williams et al., Science, 2020)

Using rings from many thousands of trees, the researchers charted dozens of droughts across the region, starting in 800 AD. Four stand out as so-called megadroughts, with extreme aridity lasting decades: the late 800s, mid-1100s, the 1200s, and the late 1500s. After 1600, there were other droughts, but none on this scale.

The team then compared the ancient megadroughts to soil moisture records calculated from observed weather in the 19 years from 2000 to 2018. Their conclusion: as measured against the worst 19-year increments within the previous episodes, the current drought is already outdoing the three earliest ones. The fourth, which spanned 1575 to 1603, may have been the worst of all — but the difference is slight enough to be within the range of uncertainty. Furthermore, the current drought is affecting wider areas more consistently than any of the earlier ones — a fingerprint of global warming, say the researchers. All of the ancient droughts lasted longer than 19 years — the one that started in the 1200s ran nearly a century — but all began on a similar path to to what is showing up now, they say.

Nature drove the ancient droughts, and still plays a strong role today. A study last year led by Lamont’s Nathan Steiger showed that among other things, unusually cool periodic conditions over the tropical Pacific Ocean (commonly called La Niña) during the previous megadroughts pushed storm tracks further north, and starved the region of precipitation. Such conditions, and possibly other natural factors, appear to have also cut precipitation in recent years. However, with global warming proceeding, the authors say that average temperatures since 2000 have been pushed 1.2 degrees C (2.2 F) above what they would have been otherwise. Because hotter air tends to hold more moisture, that moisture is being pulled from the ground. This has intensified drying of soils already starved of precipitation.

Nature drove the ancient droughts, and still plays a strong role today. A study last year led by Lamont’s Nathan Steiger showed that among other things, unusually cool periodic conditions over the tropical Pacific Ocean (commonly called La Niña) during the previous megadroughts pushed storm tracks further north, and starved the region of precipitation. Such conditions, and possibly other natural factors, appear to have also cut precipitation in recent years. However, with global warming proceeding, the authors say that average temperatures since 2000 have been pushed 1.2 degrees C (2.2 F) above what they would have been otherwise. Because hotter air tends to hold more moisture, that moisture is being pulled from the ground. This has intensified drying of soils already starved of precipitation.

Varying soil moisture in southwestern North America, 800-2018. The straight horizontal center line indicates average moisture; blue line at bottom shows 2000-2018 mean. Green bars indicate abnormally wet periods, pink ones abnormally dry. The fluctuating red moisture line is based on tree-ring data until it converts to blue at the start of modern instrumental observations. (Adapted from Williams et al., Science, 2020)

All told, the researchers say that rising temperatures are responsible for about half the pace and severity of the current drought. If this overall warming were subtracted from the equation, the current drought would rank as the 11th worst detected — bad, but nowhere near what it has developed into.

“It doesn’t matter if this is exactly the worst drought ever,” said coauthor Benjamin Cook, who is affiliated with Lamont and the Goddard Institute for Space Studies. “What matters is that it has been made much worse than it would have been because of climate change.” Since temperatures are projected to keep rising, it is likely the drought will continue for the foreseeable future; or fade briefly only to return, say the researchers.

“Because the background is getting warmer, the dice are increasingly loaded toward longer and more severe droughts,” said Williams. “We may get lucky, and natural variability will bring more precipitation for a while. But going forward, we’ll need more and more good luck to break out of drought, and less and less bad luck to go back into drought.” Williams said it is conceivable the region could stay arid for centuries. “That’s not my prediction right now, but it’s possible,” he said.

Lamont climatologist Richard Seager was one of the first to predict, in a 2007 paper, that climate change might eventually push the region into a more arid climate during the 21st century; he speculated at the time that the process might already be underway. By 2015, when 11 of the past 14 years had seen drought, Benjamin Cook led a followup study projecting that warming climate would cause the catastrophic natural droughts of prehistory to be repeated by the latter 21st century. A 2016 study coauthored by several Lamont scientist reinforced those findings. Now, says Cook, it looks like they may have underestimated. “It’s already happening,” he said.

The effects are palpable. The mighty reservoirs of Lake Mead and Lake Powell along the Colorado River, which supply agriculture around the region, have shrunk dramatically. Insect outbreaks are ravaging dried-out forests. Wildfires in California and across wider areas of the U.S. West are growing in area. While 2019 was a relatively wet year, leading to hope that things might be easing up, early indications show that 2020 is already on a track for resumed aridity.

In the Catalina Mountains in southern Arizona, forests struggle to keep up with recent increases in drought and wildfire activity, which are expected to continue due to human-caused climate change. (Park Williams/Lamont-Doherty Earth Observatory)

“There is no reason to believe that the sort of natural variability documented in the paleoclimatic record will not continue into the future, but the difference is that droughts will occur under warmer temperatures,” said Connie Woodhouse, a climate scientist at the University of Arizona who was not involved in the study. “These warmer conditions will exacerbate droughts, making them more severe, longer, and more widespread than they would have been otherwise.”

Angeline Pendergrass, a staff scientist at the U.S. National Center for Atmospheric Research, said that she thinks it is too early to say whether the region is at the cusp of a true megadrought, because the study confirms that natural weather swings are still playing a strong role. That said, “even though natural variability will always play a large role in drought, climate change makes it worse,” she said.

Tucked into the researchers’ data: the 20th century was the wettest century in the entire 1200-year record. It was during that time that population boomed, and that has continued. “The 20th century gave us an overly optimistic view of how much water is potentially available,” said Cook. “It goes to show that studies like this are not just about ancient history. They’re about problems that are already here.”

The study was also coauthored by Edward Cook, Jason Smerdon, Kasey Bolles and Seung Baek, all of Lamont-Doherty Earth Observatory; John Abatzaglou of the University of Idaho; and Andrew Badger and Ben Livneh of the University of Colorado Boulder.

From Inside Climate News (Bob Berwyn):

Warmer temperatures and shifting storm tracks are drying up vast stretches of land in North and South America.

The American West is well on its way into one of the worst megadroughts on record, a new study warns, a dry period that could last for centuries and spread from Oregon and Montana, through the Four Corners and into West Texas and northern Mexico.

Several other megadroughts, generally defined as dry periods that last 20 years or more, have been documented in the West going back to about 800 A.D. In the study, the researchers, using an extensive tree-ring history, compared recent climate data with conditions during the historic megadroughts.

They found that in this century, global warming is tipping the climate scale toward an unwelcome rerun, with dry conditions persisting far longer than at any other time since Europeans colonized and developed the region. The study was published online Thursday and appears in the April 17 issue of the journal Science.

Human-caused global warming is responsible for about half the severity of the emerging megadrought in western North America, said Jason Smerdon, a Columbia University climate researcher and a co-author of the new research.

“What we’ve identified as the culprit is the increased drying from the warming. The reality is that the drying from global warming is going to continue,” he said. “We’re on a trajectory in keeping with the worst megadroughts of the past millennia.”

The ancient droughts in the West were caused by natural climate cycles that shifted the path of snow and rainstorms. But human-caused global warming is responsible for about 47 percent of the severity of the 21st century drought by sucking moisture out of the soil and plants, the study found.

The regional drought caused by global warming is plain to see throughout the West in the United States. River flows are dwindling, reservoirs holding years worth of water supplies for cities and farms have emptied faster than a bathtub through an open drain, bugs and fires have destroyed millions of acres of forests, and dangerous dust storms are on the rise.

A similar scenario is unfolding in South America, especially in central Chile, a region with a climate similar to that in western North America. Parts of the Andes Mountains and foothills down to the coast have been parched by an unprecedented 10-year dry spell that has cut some river flows by up to 80 percent.

In both areas, research shows, global warming could make the droughts worse than any in at least several thousand years, drying up the ground and shifting regional weather patterns toward drier conditions. This is bad news for modern civilizations that have developed in the last 500 years, during which they enjoyed an unusually stable and wet climate. And assumptions about water availability based on that era are not realistic, said climate scientist Edward Cook, another co-author on the study who is also with the Lamont-Doherty Earth Observatory.

The impacts of a long-lasting drought in the West could also affect adjacent regions. A 2019 study showed that dry conditions in upwind areas may be intensifying agricultural droughts. With west winds prevailing across North America, hot and dry conditions in the Southwest could reduce the amount of atmospheric moisture available to produce rainfall farther east, in Oklahoma and Texas, for example. The study found that such drought linkages accounted for 62 percent of the precipitation deficit during the 2012 Midwest drought…

In North and in South America, researchers have identified natural climate cycles as key drivers of historic megadroughts. The most important are a combination of a warm North Atlantic Ocean and cooler-than average conditions in the eastern tropical Pacific Ocean, as well as decreased solar and volcanic activity.

“Arid periods over the last several millennia have dwarfed anything we’ve seen so far,” Smerdon said. And when the soil-drying effect of human-caused warming is added into the climate equation, the outlook is not good. Previous studies by Columbia University researchers predicted that the 21st century has a 90 percent chance of seeing a drought that lasts 25 years or longer.

He said that prospect will require people to rethink how to manage resources.

“On a regional level, this means being more proactive about water management,” Smerdon said. “There are things we can do if you recognize that the West will probably be much drier. You can start thinking about transitioning to less water intensive crops, or about beef production, which is incredibly water intensive.”

Other features “that go part and parcel with these droughts are things like forest fires and beetle infestations,” he added, noting that there were also impacts to winter recreation and tourism, with less snow for skiing and water for rafting.

Smerdon said he’s also concerned that the drought impacts are being underestimated because of an over-reliance on groundwater as a temporary buffer to the decline of river flows, and the drop of reservoir water levels. If you look at simultaneous droughts in North and South America, he said, you could also anticipate potential impacts to global food supply networks, as both regions are important for agricultural production.

The only real long-term solution is to halt greenhouse gas pollution, he said.

Photo of Lake Powell in extreme drought conditions by Andy Pernick, Bureau of Reclamation, via Flickr creative commons

From The Washington Post (Andrew Freedman and Darryl Fears):

A vast region of the western United States, extending from California, Arizona and New Mexico north to Oregon and Idaho, is in the grips of the first climate change-induced megadrought observed in the past 1,200 years, a study shows. The finding means the phenomenon is no longer a threat for millions to worry about in the future, but is already here.

The megadrought has emerged while thirsty, expanding cities are on a collision course with the water demands of farmers and with environmental interests, posing nightmare scenarios for water managers in fast-growing states.

A megadrought is broadly defined as a severe drought that occurs across a broad region for a long duration, typically multiple decades.

Unlike historical megadroughts triggered by natural climate cycles, emissions of heat-trapping gases from human activities have contributed to the current one, the study finds. Warming temperatures and increasing evaporation, along with earlier spring snowmelt, have pushed the Southwest into its second-worst drought in more than a millennium of observations.

The study, published in the journal Science on Thursday, compares modern soil moisture data with historical records gleaned from tree rings, and finds that when compared with all droughts seen since the year 800 across western North America, the 19-year drought that began in 2000 and continued through 2018 (this drought is still ongoing, though the study’s data is analyzed through 2018) was worse than almost all other megadroughts in this region.

The researchers, who painstakingly reconstructed soil moisture records from 1,586 tree-ring chronologies to determine drought severity, found only one megadrought that occurred in the late 1500s was more intense.

Historical megadroughts, spanning vast regions and multiple decades, were triggered by natural fluctuations in tropical ocean conditions, such as La Niña, the cyclic cooling of waters in the tropical Pacific.

“The megadrought era seems to be reemerging, but for a different reason than the [past] megadroughts,” said Park Williams, the study’s lead author and a researcher at the Lamont-Doherty Earth Observatory at Columbia University.

Although many areas in the West had a productive wet season in 2019 and some this year, “you can’t go anywhere in the West without having suffered drought on a millennial scale,” Williams said, noting that megadroughts contain relatively wet periods interspersed between parched years.

“I think the important lesson that comes out of this is that climate change is not a future problem,” said Benjamin I. Cook, a NASA climate scientist and co-author of the study. “Climate change is a problem today. The more we look, the more we find this event was worse because of climate change.”

Drought affected Lake Mead via the Mountain Town News

From The New York Times (Henry Fountain):

A severe drought that has gripped the American Southwest since 2000 is as bad as or worse than long-lasting droughts in the region over the past 1,200 years, and climate change has helped make it that way, scientists said Thursday.

The researchers described the current drought, which has helped intensify wildfire seasons and threatened water supplies for people and agriculture, as an “emerging megadrought.” Although 2019 was a relatively wet year, and natural climate variability could bring good luck in the form of more wet years that would end the drought, global warming increases the odds that it will continue.

“We know that this drought has been encouraged by the global warming process,” said Park Williams, a bioclimatologist at Lamont-Doherty Earth Observatory at Columbia University, and lead author of a study published Thursday in Science. “As we go forward in time it’s going to take more and more good luck to pull us out of this.”

While the term megadrought has no strict definition, it is generally considered to be a severe dry period persisting for several decades or longer. Many climate researchers and hydrologists have long thought that a Southwestern megadrought was highly likely. A 2016 study put the probability of one occurring this century at 70 percent or higher…

“Ancient megadroughts have always been seen by water managers as worst-case scenarios,” Dr. Williams said, “and we just have to hope that there’s some kind of protection measure in the climate system that’s not going to allow one of those to repeat itself. And what we’re seeing is that we’re actually right on track for one.”

[…]

since the beginning of the 20th century, when large-scale emissions of heat-trapping gases began, warming has played a role as well. Using 31 computer climate models, the researchers estimated that climate change contributed nearly half to the severity of the current drought.

Put another way, without global warming the current drought would be only of moderate severity rather than one of the worst.

While the natural variability of La Niña conditions continues, Dr. Williams said, “all of that is being superimposed on what appears to be a pretty strong long-term drying trend.”

The current drought has followed a pattern that is similar to the ancient ones, he said. Rather than one or two extremely dry years that would suddenly throw the region into drought, dry conditions have been nearly continuous and the drought has built up over time…

Brad Udall, a water and climate research at Colorado State University who was not involved in the study, said that tying the current drought to a longer-term context “fits what a lot of people have been thinking.”

Dr. Udall said the researchers’ finding that climate change accounted for about half of the drought’s severity was strongly supported by his and others’ recent studies of the shrinking flow of the Colorado River, which attribute about half of the decline to global warming.

“I love the focus on soil moisture,” Dr. Udall said of the new study. “People underappreciate how important soil moisture is.”

Soils have a buffering effect that can allow problems of water scarcity to persist even after a relatively wet year, because soils that are dry from years of drought soak up more water that would normally run into rivers and streams.

The wetter weather in 2019, for example, resulted in a deep mountain snowpack across much of the West. “But it’s increasingly clear we didn’t get the runoff we had expected,” Dr. Udall said.

The latest ancient megadrought the researchers found was the long one in the 16th century. That finding reinforces the widely held idea that conditions were relatively wetter in the Southwest for centuries before the current drought.

EPA guts rule credited with cleaning up coal-plant toxic air — Associated Press #ShameOnYou

Mercury in Colorado graphic via The Denver Post

From The Associated Press (Ellen Knickmeyer):

The Trump administration on Thursday gutted an Obama-era rule that compelled the country’s coal plants to cut back emissions of mercury and other human health hazards, a move designed to limit future regulation of air pollutants from coal- and oil-fired power plants.

Environmental Protection Agency chief Andrew Wheeler said the rollback was reversing what he depicted as regulatory overreach by the Obama administration. “We have put in place an honest accounting method that balances” the cost to utilities with public safety, he said.

Wheeler is a former coal lobbyist whose previous clients have gotten many of the regulatory rollbacks they sought from the Trump administration.

Environmental and public health groups and Democratic lawmakers faulted the administration for pressing forward with a series of rollbacks easing pollution rules for industry — in the final six months of President Donald Trump’s current term — while the coronavirus pandemic rivets the world’s attention.

With rollbacks on air pollution protections, the “EPA is all but ensuring that higher levels of harmful air pollution will make it harder for people to recover in the long run” from the disease caused by the coronavirus, given the lasting harm the illness does to victims hearts and lungs, said Delaware Sen. Tom Carper, the senior Democrat on the Senate Environment and Public Works Committee.

The EPA move leaves in place standards for emissions of mercury, which damages the developing brains of children and has has been linked to a series of other ailments. But the changes greatly reduce the health benefits that regulators can consider in crafting futures rules for power plant emissions. That undermines the 2011 mercury rule and limits regulators’ ability to tackle the range of soot, heavy metals, toxic gases and other hazards from fossil fuel power plants.

The Trump administration contends the mercury cleanup was not “appropriate and necessary,” a legal benchmark under the country’s landmark Clean Air Act.

The Obama rule led to what electric utilities say was an $18 billion cleanup of mercury and other toxins from the smokestacks of coal-fired power plants. EPA staffers’ own analysis said the rule curbed mercury’s devastating neurological damage to children and prevented thousands of premature deaths annually, among other public health benefits.

From The Deseret News (Amy Joi O’Donoghue):

Controversy over pollutants from coal-fired power plants moved to a higher level Thursday after the U.S. Environmental Protection Agency announced it had revised a cost benefit analysis over the impacts of mercury emissions regulations imposed during the Obama era.

The federal agency said the restrictions on mercury emissions through technology controls were not justified, backing a 2015 U.S. Supreme Court decision that directed the agency to complete another review.

EPA Administrator Andrew Wheeler, in a teleconference, said the 2012 Obama-era rule remains in place and no additional mercury emissions will happen due to the revised analysis.

He added that critics of the Thursday announcement are either purposefully misreading the revisions or don’t understand…

In a major victory for the energy industry, the U.S. Supreme Court ruled against federal regulators’ attempts to curb mercury emissions from power plants in 2015, saying the government wrongly failed to take cost into consideration.

The 5-4 decision overturned the landmark rule, which was the first attempt by the EPA to curb mercury and other pollutants from coal-fired power plants.

Michigan’s lawsuit against the regulation was joined by 21 other GOP-led states, including Utah, in a fight to get it tossed.

The new “supplemental cost finding” announced by the federal agency found compliance costs for mercury emissions at power plants ranging from $7.4 billion to $9.6 billion annually due to the rule and the benefits in terms of reduction in costs such as health care to be around $6 million.

Wheeler added that the Obama administration’s approach was that any new regulation could be justified, regardless of the cost…

Moms Clean Air Force issued a statement expressing its outrage over the move.

“While America suffers devastating public health impacts of the coronavirus outbreak — a lethal respiratory pandemic — Andrew Wheeler and the Trump administration continue their cynical campaign to protect industrial polluters and undermine lifesaving pollution protections,” said co-founder Dominique Browning.

The organization added that the EPA is gambling with the health of children by giving any sort of nod to coal-fired power plants.

Wheeler dismissed any criticism, again reiterating the revision released Thursday was the result of a court-directed action to correct flaws of a previous administration’s conclusions over costs and benefits.

Journey to the top of the watershed — Platte Basin Timelapse

Click through to view the film (Carlee Koehler):

In June, a small team of PBT interns set out for the highest point in the Platte Basin watershed.

We had big intentions of catching 5-star media to fill in cracks for the Grays Peak scene in the upcoming PBT documentary featuring Mike and Pete’s 55-day, 1,300-mile journey across the watershed.

Grays and Torreys, Dillon Reservoir May 2017. Photo credit Greg Hobbs.

Grays Peak is the highest point in the Platte Basin watershed. The mountain, located west of Denver in the Front Range of Colorado, is ranked as the tenth-highest summit of the Rocky Mountains of North America. With the top reaching an elevation of 14,278 feet, it may be considered to some as quite a commitment to reach the top.

The beginning of the trip went as intended. We had the car loaded with all of our equipment and prepared a schedule that would allow us enough time to focus on what we needed to do, or so we thought.

After incidents of altitude sickness, a split hiking boot, bird invasions, and a major bear spray accident, we all accepted our humorous situation of what the trip turned into. We came back with quite the story for the rest of the PBT team. Nevertheless, we agreed the trip had been a successful one and after arriving back in Lincoln, made the best out of what we managed to capture.

The Platte River is formed in western Nebraska east of the city of North Platte, Nebraska by the confluence of the North Platte and the South Platte Rivers, which both arise from snowmelt in the eastern Rockies east of the Continental Divide. Map via Wikimedia.

Streamflow forecast down for Roaring Fork despite above-normal snowpack — @AspenJournalism #ColoradoRiver #COriver #aridification

The Roaring Fork River (left) joins with the Colorado River in downtown Glenwood Springs. Snowpack in the Roaring Fork basin is slight above normal, but April streamflows are predicted to be just 85% of normal. Photo credit: Heather Sackett/Aspen Journalism

From Aspen Journalism (Heather Sackett):

Although snowpack in the mountains near Aspen is hovering above normal for this time of year, streamflows in the Roaring Fork River are predicted to be just 85% of normal for April.

The snow-telemetry, or SNOTEL, site at Independence Pass, near the headwaters of the Roaring Fork River, is at 106% of normal snow-water equivalent. The SNOTEL site at Kiln, near the headwaters of the Fryingpan River, is at 106% of normal. And at Scofield Pass, home to the headwaters of the Crystal River, the SNOTEL site shows snowpack at 90% of normal. The Roaring Fork basin as a whole is at 112% of normal snowpack.

But the April water-supply outlook released by the National Resources Conservation Service predicts streamflows at just 85% of normal at the confluence of the Roaring Fork and Colorado rivers in Glenwood Springs.

“It’s kind of an anomalous year,” said Karl Wetlaufer, a hydrologist with NRCS and assistant supervisor with the Colorado Snow Survey. “More commonly, the streamflow forecasts do pair with the snowpack pretty well.”

Colorado Drought Monitor April 14, 2020.

The reason for the discrepancy is dry soils, which soak up spring snowmelt before it gets to streams. According to the U.S. Drought Monitor, abnormally dry conditions crept back into Pitkin County in mid-September. By Oct. 22, the western half of the county was in severe drought, while the eastern half was in moderate drought. The western half of Pitkin County is still experiencing either abnormally dry conditions or moderate drought.

“All of late summer was really dry, but before the snow started to accumulate, it was extremely dry,” Wetlaufer said. “The soil can be like a really dry sponge right now and soak up more runoff than usual.”

That lower-than-normal runoff could have impacts on the city of Aspen, which takes its municipal water supply directly from Castle and Maroon creeks. Tyler Christoff, director of Aspen’s utilities department, said city staff is constantly monitoring the variables in the watershed — U.S. Geological Survey gauges, SNOTEL sites, weather forecasts, Drought Monitor — but so far, they are treating this as an average year.

“Being close to average, we are going to let it play out and see if there’s any action we need to take,” Christoff said. “I think regardless of the year and the season, it’s important for our community to be conscious of our use of water as a resource; we do not have an unlimited supply.”

The Colorado River basin typically reaches its peak snowpack for the year in early to mid-April.
NRCS has two main ways of measuring snowpack, which feed into the water-supply forecasts. The first is through SNOTEL sites, which are an automated system of sensors that collect weather and climate data hourly from 115 areas around Colorado, mostly in remote, mountainous watersheds between 9,000 and 11,000 feet. They measure snow depth, water content of the snow, precipitation and air temperature.

Karl Wetlaufer (NRCS), explaining the use of a Federal Snow Sampler, SnowEx, February 17, 2017.

The other way is through snow courses, which are manual measurements of snow depth and water content.

But due to the COVID-19 crisis, NRCS staff did not conduct end-of-March manual snow surveys. Wetlaufer said the agency wanted to follow social-distancing guidelines and not have employees traveling in the same vehicle to remote mountain communities.

“We need to go out in pairs for backcountry work,” he said. “We have been talking about options for next month. Some sites that are key, maybe we can still go out and drive two vehicles.”

But streamflow forecasts for the Colorado River basin barely use any snow-course data, Wetlaufer said, so those forecasts should still be accurate without the manually collected data.

“In the Colorado River basin, there’s really pretty minimal impact,” he said.

Aspen Journalism collaborates with The Aspen Times and other Swift Communications newspapers on coverage of water and rivers. This story ran in the April 13 edition of The Aspen Times.

Map of the Roaring Fork River drainage basin in western Colorado, USA. Made using USGS data. By Shannon1 – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=69290878

Lack of data makes predicting COVID-19’s spread difficult but models are still vital — The Conversation #COVID19 #coronavirus


Public health authorities rely on models to make decisions but how accurate are they?
Sarah Silbiger/Getty Images

Lester Caudill, University of Richmond

Editor’s note: The question everyone in the world wants answered is how far the new coronavirus will spread and when the pandemic will begin to ebb. To know that, epidemiologists, public health authorities and policymakers rely on models.

Models are not meant to predict the future perfectly – yet they’re still useful. Biomedical mathematician Lester Caudill, who is currently teaching a class focused on COVID-19 and modeling, explains the limitations of models and how to better understand them.

What are infectious disease models?

Mathematical models of how infections spread are simplified versions of reality. They are designed to mimic the main features of real-world disease spread well enough to make predictions which can, at least partly, be trusted enough to make decisions. The COVID-19 model predictions reported in the media come from mathematical models that have been converted into computer simulations. For example, a model might use a variety of real world data to predict a date (or range of dates) for a city’s peak number of cases.

Why is modeling the spread of COVID-19 challenging?

In order for a model’s predictions to be trustworthy, the model must accurately reflect how the infection progresses in real life. To do this, modelers typically use data from prior outbreaks of the same infection, both to create their model, and to make sure its predictions match what people already know to be true.

This works well for infections like influenza, because scientists have decades of data that help them understand how flu outbreaks progress through different types of communities. Influenza models are used each year to make decisions regarding vaccine formulations and other flu-season preparations.

By contrast, modeling the current COVID-19 outbreak is much more challenging, simply because researchers know very little about the disease. What are all the different ways it can be transferred between people? How long does it live on door knobs or Amazon boxes? How much time passes from the moment the virus enters a person’s body until that person is able to transmit it to someone else? These, and many other questions, are important to incorporate into a reliable model of COVID-19 infections. Yet people simply do not know the answers yet, because the world is in the midst of the first appearance of this disease, ever.

Disease models are built on assumptions and historical data collected from other diseases. Having relatively little epidemiological data on COVID-19 adds uncertainty to models of how it will spread.
AP Photo/Jon Elswick

Why do different models have different predictions?

The best modelers can do is assume some things about COVID-19, and create models that are based on these assumptions. Some current COVID-19 models assume that the virus behaves like influenza, so they use influenza data in their models. Other COVID-19 models assume that the virus behaves like SARS-CoV, the virus that caused the SARS epidemic in 2003.

Other models may make other assumptions about COVID-19, but they must all assume something, in order to make up for information that they need, but that simply does not yet exist. These different assumptions are likely to lead to very different COVID-19 model predictions.

How can people make sense of the different – sometimes conflicting – model predictions?

This question gets at, perhaps, the most important thing to know about mathematical model predictions: They are only useful if you understand the assumptions that the model is based on.

Ideally, model predictions like, “We expect 80,000 COVID-related deaths in the U.S.” would read more like, “Assuming that COVID-19 behaves similar to SARS, we expect 80,000 COVID-related deaths in the U.S.” This helps place the model’s prediction into context, and helps remind everyone that model predictions are not, necessarily, glimpses into an inevitable future.

An oft-cited model from Institute for Health Metrics and Evaluation at the University of Washington has a wide range of projections for deaths from COVID-19. They vary based on different underlying assumptions and how they change, such as the effect of social distancing or widespread testing.
Institute for Health Metrics and Evaluation at the University of Washington

It may also be useful to use predictions from different models to establish reasonable ranges, rather than exact numbers. For instance, a model that assumes COVID-19 behaves like influenza might predict 50,000 deaths in the U.S. Rather than trying to decide which prediction to believe – which is an impossible task – it may be more useful to conclude that there will be between 50,000 and 80,000 deaths in the U.S.

Why do the same models seem to predict different outcomes today than they did yesterday?

As COVID-19 data becomes available – and there are many good people working tirelessly to gather data and make it available – modelers are incorporating it so that, each day, their models are based a little more on actual COVID-19 information, and a little less on assumptions about the disease. You can see this process unfold in the news, where the major predictive COVID-19 models provide almost daily revisions to their prior estimates of case numbers and deaths.

Can a model that’s (probably) not accurate at predicting the future still be useful?

While models of infections can provide insights into what the future might hold, they are far more valuable when they help answer, “How can policies alter that future?”

For instance, a baseline model for predicting the future number of COVID-19 cases might be adapted to incorporate the effects of, say, a stay-at-home order. By running model simulations with the order, and comparing to model simulations without the order, public health authorities may learn something about how effective the order is expected to be. That can be especially useful when comparing the associated costs, not only in terms of disease burden, but in economic terms, as well.

One step further, this same model could be used to predict the consequences of ending the order on, say, June 10 – the current target date for the stay-at-home order in Virginia – and compare them to model predictions for ending the order on, say, May 31 or June 30. Here, as in many other settings, models prove to be most useful when they’re used to generate different scenarios which are compared to each other. This is different than comparing model predictions to reality.

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Lester Caudill, Professor of Mathematics, University of Richmond

This article is republished from The Conversation under a Creative Commons license. Read the original article.

#Drought news: Areas of #Colorado, #Kansas and SW #Nebraska 2-4F above normal, E. #CO and SW #KS remain the driest portion of the High Plains

Click on a thumbnail graphic to view a gallery of drought data from the US Drought Monitor.

Click here to go to the US Drought Monitor website. Here’s an excerpt:

This Week’s Drought Summary

An active pattern brought snow, rain, thunderstorms and severe weather over much of the United States. Most of the precipitation was east of the Missouri River valley and the greatest amounts were centered over Tennessee, Arkansas, Kentucky, western Virginia and the northern portions of Mississippi, Alabama, and Georgia, where more than 3 inches of rain was widespread. Southern California also had record-breaking rains continue, while snow was recorded in portions of the northern Plains and Midwest. Temperatures were generally warmer than normal over the country with just the Southwest and northern Plains being below normal. The greatest departures were in Florida where temperatures were 6-8 degrees above normal for the week and in Montana and southern California where temperatures were more than 10 degrees below normal…

High Plains

It was mostly dry over much of the region this week with just areas of northern Wyoming, southwest South Dakota, and north-central Nebraska recording above-normal precipitation. Temperatures were below normal in the Dakotas, northern Nebraska, and Wyoming with departures of up to 8 degrees below normal. Areas of Colorado, Kansas and southwest Nebraska were above normal with departures of 2-4 degrees above normal. There are some pockets of dryness developing in portions of Nebraska and Kansas, but no changes were made there this week, although the area of south-central Nebraska and central Kansas is trending toward the introduction of abnormally dry conditions. Eastern Colorado and southwest Kansas remain the driest portion of the High Plains. Severe drought was expanded over southeast Colorado this week and moderate drought and abnormally dry conditions were pushed eastward. This area will need to be watched for further degradation in the weeks ahead…

West

Most of the region was dry this week outside of a few areas in Montana and western Wyoming while in the Southwest, record-setting rains continued in southern California and into Arizona. Over the last 6 weeks, areas in and around Kern County, California have gone from significant precipitation deficits to well above normal readings accompanied by flooding in the region. Most of southern California recorded 800 percent of normal precipitation just in the last week and 200-400 percent of normal over the last 30 days. Temperatures were cooler than normal over the southwest areas of the west and Montana while most of the rest of the region was 2-4 degrees above normal and northern California was 6-8 degrees above normal. The current water year has been dry over much of the region and this has allowed further degradations to be shown in portions of northern California up to Washington. In western Oregon, the current conditions are similar to 2000-2001 and 2004-2005 with the exception of the near-normal snowpack. Some counties in southwest Oregon are reporting the earliest start to the irrigation season since 2000-2001 with several counties preparing to file drought declarations with the state of Oregon. Severe drought was expanded over much of northwest California northward into Oregon. Severe drought was also expanded in the interior of Washington. Abnormally dry conditions and moderate drought were also expanded over eastern and western portions of Oregon and Washington this week as well as western Montana and northern Idaho. In southern California, moderate drought and abnormally dry conditions were removed from Kern County and vicinities in response to the record-breaking precipitation. Improvements were also made to areas of severe and moderate drought in northeast Arizona and to abnormally dry areas of northeast and north central Arizona…

South

Warmer than normal temperatures were widespread throughout the region with departures of 6-8 degrees above normal along the Gulf Coast. Precipitation was mixed over the area with portions of southeast Oklahoma, central to southern Texas, Arkansas and northern Louisiana and Mississippi all recording well above normal precipitation with readings of 150-400 percent of normal. Conditions remained dry over the Gulf Coast as well as west Texas. In west Texas, moderate drought was introduced and abnormally dry conditions were expanded this week. In central and south Texas, there was a mix of degradations and improvements as some areas were still realizing the impact of previous rains that allowed for some areas of extreme and severe drought to improve. A new area of severe drought was introduced in far southeast Louisiana and some improvements were made to the abnormally dry conditions in Mississippi. There is a very tight gradient setting up going inland from the Gulf Coast as these coastal areas continue to miss out on any precipitation and have had above-normal temperatures too…

Looking Ahead

Over the next 5-7 days, it is anticipated that the eastern half of the United States will stay quite wet, with the Southeast projected to record the most precipitation. Some relief may come to the Gulf Coast region as well. The Northern Plains and upper Midwest look to be dry while the central and southern Plains will see up to an inch of precipitation. Precipitation looks to be scattered through the West with some upper elevations seeing the most precipitation. Temperatures during this time are expected to be cooler than normal over most of the United States with departures of 9-12 degrees below normal over the Midwest to New England.

The 6-10 day outlooks show much of the central U.S., West, Southeast, and Alaska having a greater than normal probability of above-normal temperatures while the Midwest and Northeast show a higher than normal probability of below-normal temperatures. The greatest probabilities of recording above-normal precipitation are over the Four Corners into the south to the Southeast and interior Alaska.

US Drought Monitor one week change map ending April 14, 2020.