Paul DuginskiSat, September 25, 2021, 5:00 AM·4 min read
Increasing evaporative demand is escalating summertime drought severity in California and the West, according to climate researchers.
Evaporative demand is essentially the atmosphere’s “thirst.” It is calculated based on temperature, humidity, wind speed and solar radiation. It’s the sum of evaporation and transpiration from plants, and it’s driven by warmer global temperatures, which can be attributed to climate change.
The meteorological summer of 2021 in the contiguous United States, which runs from June through August, tied the extreme heat of the Dust Bowl summer in 1936.- ADVERTISEMENT -https://s.yimg.com/rq/darla/4-6-0/html/r-sf-flx.html
California and the West have seen a substantial increase in evaporative demand over the last half-century, worsening summer drought severity, said John Abatzoglou, an associate professor and climate scientist at UC Merced.
The drought in California isn’t just the result of a scarcity of precipitation. It is a combination of two things: a lack of rain and those thirsty atmospheric conditions that desiccate the landscape. For much of California, the 2021 summer and water year have had the highest evaporative demand in the last 40 years, according to the National Integrated Drought Information System.
As Abatzoglou points out, Northern California has endured the third-driest water year on record along with the highest recorded evaporative demand — factors that “place this year in a class by itself.” These things are remarkable, he adds, “given that the California drought hall of infamy is notorious.”
Abatzoglou cites the Palmer Drought Severity Index, which he describes as a general catch-all drought index widely used in the U.S., and part of what informs the U.S. Drought Monitor. According to that yardstick, Northern California is having its worst year in the instrumental record. The PDSI is a soil moisture index that accounts for both precipitation and evaporative demand.
Abatzoglou sees the “demand” side of the drought as something we’re beginning to appreciate. He says there have been dry droughts and then there have been hot and dry droughts. The latter have promoted increased summertime irrigation demands by agriculture in the Central Valley, energy imbalances due to higher demand caused by heat and reduced energy supply due to the reduction in hydroelectric power generation.
The latest U.S. Drought Monitor report, released Thursday, paints a dire picture of the situation in California and much of the West — as it has for months. In the current data, about 46% of the state is categorized as being in exceptional drought, while just over 42% is in extreme drought. The remaining approximately 12% of the state is about evenly divided between moderate and severe drought — meaning that 100% of the state is stricken by some level of drought.
Increased evaporative demand has exacerbated the dryness in vegetation that has enabled more wildfires this year. Active wildfires such as the Windy fire and the KNP Complex fires were among those that continued to consume parched vegetation in California.
The areas of exceptional and extreme drought in the Drought Monitor map track fairly closely with the pattern where evaporative demand in the state — that measure of a thirsty atmosphere — ranks as the highest on record for June through August. This oxblood-colored part of the map indicates the biggest departures from normal from California summers from 1980 to 2021.
In November, Science Daily quoted Abatzoglou as saying: “Increased evaporative demand with warming enables fuels to be drier for longer periods. This is a recipe for more active fire seasons.”
That prediction has been borne out in the summer of 2021.
Furthermore, in an April 2020 paper in the journal Science, on which Abatzoglou was one of the authors, the massive, continuing drought afflicting the U.S. Southwest was estimated to be 46% more acute because of human-caused climate change.
Another study a few years ago, by Abatzoglou and others, estimated that the 2012-2014 drought in California was 8% to 27% more severe because of a warming climate.
There have always been cyclical droughts in California and the West, but scientific evidence indicates that human-caused climate change is creating a warmer, thirstier atmosphere that sucks the moisture out of the landscape.
“The increase in evaporative demand is akin to putting an additional straw in one’s drink,” Abatzoglou said. “It is now that much easier to drain the cup.”
BY PARK WILLIAMS, BEN COOK AND JASON SMERDON, OPINION CONTRIBUTORS — 07/23/21 04:15 PM EDT 295THE VIEWS EXPRESSED BY CONTRIBUTORS ARE THEIR OWN AND NOT THE VIEW OF THE HILLShare to Facebook Share to Twitter
Summer for many Americans is the time to enjoy being outside. But for much of the United States, this year’s extreme drought, wildfires, smoke and heat waves have made enjoying outdoor activities nearly impossible and continue to threaten the livelihoods and health of people and ecosystems across the country. With summer 2021 barely half over, and conditions likely to worsen in coming months, these extreme conditions provide a stark reminder that the chronic impacts of climate change will be one of our greatest 21st-century challenges.
As bad as 2021 has been, the story of drought in the West doesn’t begin this year. Since 2000, severe drought has drained western reservoirs, increased ground-water extraction, promoted giant wildfires and forest die-off, and coincided with ever-intensifying heat waves. We’ve had a bit of a bad run.
But how bad has that run really been? Pretty bad, actually. In 2020, our research team published a study demonstrating that 2000 to 2018 was among the worst 19-year drought periods in at least 1200 years, second only to a so-called “megadrought” in the late 1500s.
Now, 2021 is shaping up to be the region’s most severe drought year in modern history, pushing the 2000s drought into its 22nd year, an over two-decade-long event that will likely be the West’s driest 22-year period in at least 1,200 years. In other words, 2021 will probably be remembered as a fork in the road for western drought, when an already long and severe drought had a big growth spurt and entered legitimate megadrought territory.
The term megadrought arose in the 1990s through the study of tree-ring records. Measurements from many thousands of trees across the West give us an exceptionally accurate record of annual soil-moisture conditions that stretches back more than 1,200 years. It is in this record that the story of megadroughts — severe droughts that stretched on for multiple decades or even a century — has been revealed.
From 800 AD to 1600 AD, the West suffered four megadroughts, each pummeling the region with intense and prolonged dry conditions. A megadrought in the 1200s is especially infamous because it lasted the better part of a century and coincided with the depopulation of indigenous cliff-dwelling settlements in the Southwest. The last of the megadroughts left its mark in the late 1500s, lasting approximately 30 years and including the year 1580 CE, the worst single drought year in at least 1,200 years.
As of July, our projected estimates indicate that 2021 will very likely finish among the worst three to five drought years in the past 1,200 years. These exceptionally dry conditions will push the 2000s drought to the top, overtaking the 1500s megadrought as the event with the driest 22-year period in more than a millennium. Will the current drought soon end — or will it survive to 30 years, the age of the 1500s megadrought, or persist even longer? We don’t know, but it will take more than just one or two lucky wet years to make up for the dryness accumulated since 2000.
A difference between the current megadrought and those of the past is that it has not exclusively been a matter of chance — this drought has been strengthened by human-caused climate change. Warming from greenhouse-gas emissions enhances the atmosphere’s thirst for moisture from soils, plants and lakes. Warming also reduces mountain snowpack and may even push storm tracks north — away from the dry southwestern United States. Based on climate model simulations, our best estimate is that human-caused warming trends account for 30 to 45 percent of the severity of the 2000s drought so far. In other words, if the last two decades of fickle storms in the West had occurred without human-caused warming, the resulting drought would have been serious, but not in the same ballpark as the megadroughts of the past.https://0d7acd2f19bc9603b1df26f952ce455d.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html
This assessment that warming worsens droughts in the West is not based solely on climate modeling. The Earth has been faithfully storing clues about its environmental history in more than just tree rings. Shorelines and mud sediments from ancient lakes, vegetation preserved in pack-rat nests, and other natural archives point to profound drying across the West as the globe warmed coming out of the last glacial period approximately 12,000 to 15,000 years ago, and again roughly 6,000 years ago when the Northern Hemisphere received its most sunlight in 100,000 years. The message from these past periods is clear: when the globe warms, the West dries.
Multiple lines of evidence indicate that human-caused warming will continue to load the dice toward increasingly severe and longer-lasting droughts in the western US. A western water crisis may very well be underway and the ever-increasing risks require that drought resilience locally must be immediately pursued, while greenhouse-gas reductions must be an urgent priority globally.
Yes, there’s been a lot of bad news lately, but the good news is that our science has given us the ability to anticipate the future. That power has alerted us to the seriousness of the risks we may face, but it has also given us the power to influence how the future will unfold.
The choice is ours, but as we ponder our decision it may be wise to reflect on the words of the late Nobel laureate, Sherwood Roland: “What’s the use of having developed a science well enough to make predictions if, in the end, all we’re willing to do is stand around and wait for them to come true?”
The American West was once seen as a place of endless possibilities: grand vistas, bountiful resources, and cities that somehow grew out of deserts. Now, manifest destiny has become a manifest emergency.
A scorching drought made worse by climate change is draining reservoirs at an alarming pace, fueling massive wildfires and deadly heat waves, and withering one of the most important agricultural economies in the country.
He showed correspondent Ben Tracy a field of dirt that he’s left fallow – there’s not enough water to plant a crop here this summer.
Tracy asked, “How much of your land have you left unplanted this year?”
“About a third,” he replied. “That’s significant. If that water doesn’t get here, we will start to lose our crops. Some of our crops will probably die.”
Del Bosque’s water comes from the San Luis Reservoir, which is at just 30% of its capacity. The state has now cut water deliveries to many of its farmers who supply much of the nation’s fruits, nuts and vegetables.
Tracy asked, “I’m sure you talk to your neighbors, to farmers up and down the valley. What are people saying?”
“Well, a lot of them are worried, and a lot of them are mad,” Del Bosque said. “If we have no water, we can’t farm. If we get no water next year, these trees won’t get water. They’re gonna die.”
This devastating drought is not confined to California; it’s impacting nearly all of the West.
The red and brown colors on this map are what the government calls “severe and exceptional drought.”
“This drought is really bad; it’s one of the worst handful of years since the year 800 A.D.,” said Park Williams, a hydroclimatologist at UCLA. He said this is not just one long, hot dry summer, but what scientists call a “megadrought.”
“This is really the 22nd year of a long drought that began in the year 2000,” Williams said.
He and his colleagues know this from studying the rings on trees, which show how much they grow in any given year. “The last 22 years actually rank as the driest 22-year period in at least 1,200 years, based on tree ring records,” Williams said. “And so, humans now are contending with a water limitation crisis in the West that modern society in this region has not yet had to contend with.”
We’ve long known the limitations of the arid West. In the mid-1800s the U.S. government sent geologist John Wesley Powell to survey the Western U.S. water supply and bring back recommendations.
Williams said, “He warned that the West did not have enough water for a really widespread population. And we kind of bent the rules along the way when we started figuring out how to dam up the Colorado River and divvy it up to the Western states.”
Hoover Dam, an engineering marvel, was thought to be a concrete solution. It harnessed the mighty Colorado River, and created Nevada’s Lake Mead, still the nation’s largest reservoir. This water supply is what made Western cities such as Los Angeles, Phoenix and Las Vegas possible, and allowed us to create some of the richest farmland in the country.
But the predicted water supply from the Colorado River was based on 20 abnormally wet years at the beginning of the last century. Now, 40 million people in seven states depend on it.
“We did it. We built it. We’ve become reliant on it,” said Pat Mulroy, the former head of the Southern Nevada Water Authority. “So, we have to deal with what we have.”
Tracy met Mulroy on the shores of Lake Mead, which has sunk to its lowest level ever. In the year 2000, the water came right up to the top of Hoover Dam. During the megadrought, the lake has dropped more than 140 feet.
“When it loses this much water, to me that is an enormous wakeup call,” Mulroy said.
Next month the federal government is expected to make an unprecedented decision: declaring a first-ever shortage on the river, triggering cuts to the water supply in Arizona and Nevada that will cost some farmers 25% of their water.
“It’s a tipping point,” Mulroy said. “It’s an existential issue for Arizona, for California, for Nevada. It is a river system and a water supply that cannot fail.”
Tracy asked, “Without this, are places like Phoenix and Las Vegas and Los Angeles possible?”
“No, absolutely not. They’re not possible. At the end of the day, this is gone, and those cities and that economic base is in dire jeopardy.”
What the West needs more than anything is snow. Snowpack in the mountains melts throughout the summer and flows into reservoirs.
“In the West, snow is like our battery; it’s where we store water,” said J.T Reager, a water scientist at NASA’s Jet Propulsion Laboratory. “Now, we’re getting less snow. The snow season is markedly shorter.”
“Is this something that is caused by climate change or something that’s just made worse by climate change?”
“I think it’s something that’s definitely made worse by climate change,” Reager said.
Climate change is making the West hotter and drier, which means more rain than snow is falling, and much of that is evaporating.
“Over the long-term, what we’re seeing with our satellite data is a picture of continual drying,” Reager said.
A NASA satellite is documenting the loss of water stored in the mountains, reservoirs, and underground aquifers. “These are some images that we’ve taken from the satellite mission from April 2010, 2015 and 2021, showing this steady drying progression of water in the West,” Reager said.
“Given how severe this drought is,” asked Tracy, “how long would it take to recover from something like this?”
“We would need a solid decade of really wet years, which is probably just not gonna happen,” he replied.
Joe Del Bosque has already let 70 of his farm workers go, and isn’t sure how long his farm will survive if the drought drags on.
Tracy asked, “If you were starting all over, knowing what you know about this climate now, would you do this?”
“I don’t know,” he replied. “It was like a dream for me to be able to do this. Because I was the son of farm workers. I have a lot of people that depend on me. There’s hundreds of people working in the fields, picking melons, that are people just like my ancestors, that came here, worked hard to try to make a living for their kids, so their kids could go to college like I did. And this is gonna end their dream, too.”
One of the fastest-warming regions of the U.S. is the Southwest — and that region, plus the broader West, is stuck in its most expansive and intense drought of the 21st century.
Why it matters: Studies show that a warming climate is exacerbating the drought, and in some ways may be triggering it in the first place. That means the Southwest is drying out — and California’s large wildfires could start as soon as next month.
And one climate researcher says California’s Sierra Nevada Mountains saw one of the fastest snow melt-outs in history this year.
The drought situation is particularly severe in the Colorado River Basin and northern California. Scientists and public officials are warning that the California wildfire season is likely to be severe, due to the combination of dry vegetation and above-average temperatures.
This one comes on the heels of the worst fire season in state history, which turned the skies above San Francisco a “Blade Runner” orange last year.
The big picture: Some parts of the world are already getting close to, or have slipped beyond, the Paris agreement’stemperature limit thatscientists warned about in a report last week.
As Earth’s temperatures tick upwards, closer to the Paris guardrail of 1.5°C (2.7°F) above preindustrial levels, some parts of the world are already warming by much greater amounts, from the Southwestern U.S. to the Arctic. These areas are seeing destructive impacts that are mounting.
Details: California’s Sierra Nevada Mountains show what climate change can do as it worsens. The mountain snowpack, which provides 30% of the state’s water supply annually, has vanished about two months ahead of schedule.
Water runoff from snow melt has been paltry, and major reservoirs like Lake Oroville are running even lower than they did during the record drought from 2012-2016.
Climate change is playing a key role in the drought, by boosting temperatures and increasing the loss of water to the atmosphere. Much of the snow went directly from frozen form back into the air, rather than melting into runoff.
Warming is also thought to be leading to increasing chances of dry fall seasons in the Golden State and shortened rainy seasons, according to Daniel Swain, a climate researcher at UCLA and the Nature Conservancy.
Craig Clements, who studies wildfires at San Jose State University, warns that large wildfires typically not seen until late summer in California could occur this year as early as June. Vegetation is at near record dry levels for this time of year, he said.
“We are starting off in a more dire situation than we typically would for June,” Clements told Axios.
Context: The worsening drought and potentially devastating wildfire season is not an isolated occurrence for California and other Southwestern states.
Climate studies have consistently shown that as the world continues to warm, the Southwest will become drier and hotter. This is worrisome, given the likelihood of increased stress on water resources amid a population boom in states such as Arizona and Nevada.
Although it’s interspersed with short intervals of wetter years, parts of the West, including California, are suffering through an emerging, human-caused “megadrought” that began in 2000.
Studies show this drought, measured using soil moisture data and tree rings, is the second-worst in the past 1,200 years.
What they’re saying: “This current drought has quickly accelerated, and is now on par (if not worse) than the extreme and in some cases record-breaking drought that occurred just 5 years ago in California,” Swain said.
What’s next: If the world does not steeply reduce greenhouse gas emissions starting in this decade, more areas will warm to near or above the Paris limits, until the global average arrives at that level as well.
This threatens to unleash catastrophic impacts, such as the melting of parts of the Antarctic Ice Sheet.
For now, the drought and likely severe wildfire season in the West offer an unfortunate preview of what may come next.
Nearly a century ago, the people who built Hoover Dam on the Colorado River were “inspired by a vision of lonely lands made fruitful,” as the inscription at the base of the flagpole on the Nevada side puts it. They could not know they were living in what would prove to be the wettest century of the past millennium in the American West.
We sure know that now. The “megadrought” that began right at the turn of the 21st century is still going on, and this year is shaping up to be a bad one, in part due to climate change, Alejandra Borundawrites for Nat Geo.
Most of California was declared under drought emergency Monday, mainly because the snowpack that Californians depend on to help tide them through summer is at 15 percent of its average for this time of year (pictured above, Lake Oroville, at 42 percent capacity in late April). Most of the Colorado River Basin is in a state of “exceptional” drought. Lake Mead, the reservoir behind Hoover, has fallen more than 130 feet since 2000. It’s nearing the level at which water managers would have to declare an official shortage for the first time—and start limiting releases from the lake.
When I visited Hoover for a 2008 Nat Geo feature—the drought was already worrisome then—I met a man named Terry Fulp, who managed releases from Lake Mead for the federal Bureau of Reclamation. We talked about how the water had been too cheap for too long. “Our job was to entice people to move to the West, and we did a darn good job,” Fulp said. When we spoke, though, he was focused on a different job—negotiating the shortage rules that may soon kick in, depending on how the summer goes. They could cause Arizona, for example, to receive about 166 billion gallons less of Colorado River water next year.
Judging from tree rings, today’s megadrought is the second worst in 1,200 years, Borunda writes. It’s worse than the one that, in the 13th century, led Ancestral Pueblo people to abandon the famous cliff dwellings at Mesa Verde. There’s no mass flight out of the West so far: In most Colorado River Basin states, the population is growing faster than the national average, according to the latest census figures.
Accommodating all those folks in an era of climate change is going to take major adjustments, but we have tools today that weren’t available to the Ancestral Puebloans. People are already taking steps to adapt (see box below). We need the same kind of optimistic self-confidence as the builders of Hoover Dam, but a different vision: a vision of arid lands kept livable.
As parts of the Western US emerge from one of the driest winter seasons on record, the expectation of yet another summer of wildfires will be familiar to many.
Scientists, in fact, are already issuing warnings of an increased risk of wildfires in places such as California for 2021, and other parts of the Western US, as the San Francisco Chronicle recently reported.
The region, where wildfires are increasingly common, is ripe for wildfires following a winter with extremely dry conditions – and reportedly the third worst ever seen.
And it could for a single reason – what is being described by scientists as the second worst drought for 1,200 years.Scientists Begin Studying ‘The Year Of The Quiet Ocean’PauseNext video0:00 / 0:00SettingsFull-screen
The Western US, a region at the front of the world’s fight against a warming climate, is on the verge of a “mega drought”, according to a report by CBS, following analysis of the US Drought Monitor and warnings from scientists.
The period of so-called “mega drought”, of which the consequences are only starting to be seen, is thought to have begun in 2000, with peaks in periods of severe drought – and wildfires.
As shown in figures from the National Oceanic and Atmospheric Administration (NOAA), the period was responsible for the two worst droughts to occur, in 2003 and 2013.WEEKLY EXCLUSIVE EMAIL
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Figures for 2020-2021 are more alarming, with the amount of area being in a state of “exceptional drought” at 20 per cent – wider than at any point for 20 years.about:blank
Craig Clements, a professor at California’s only wildfire research centre, told the Chronicle that “the lack of rain this season has severely impacted” the moisture of the ground – or its ability to catch alight.
Roughly 60 per cent of Western states are currently under severe, extreme or exceptional drought, according to The US Drought Monitor. The region’s reservoirs are also at half of their operating capacity.
It follows winter temperatures ranging from 4 to 15 degrees above average for Western states, and a lack of snowfall — immediately after the worst wildfire event for California in 2020, and another summer of below average rainfall.
Scientists argue that it could end with permanent drought for swathes of the Western US, which could soon become unable to recover from recurring dry winters and summers.
Reasons for the “mega drought” are twofold, a warming climate caused by human activity, and in the short term, a La Niña event in which cooler waters in the Pacific are failing to provide moisture.
“It’s hard to say if it’s going to be worse, but it could be very similar,” Mr Clements added of the current conditions. “As long as we don’t have a lightning event, we should be in better shape, but our fuels are not.”
The gold standard for the measurement of drought in America is the U.S. Drought Monitor. It measures drought levels down to the state level. It shows that vast parts of the western United States have been hit by the worst drought in years and, in some cases, more than a century. Scientists have a plan to combat this, and it is not entirely new.https://www.dianomi.com/smartads.epl?id=3533
The Drought Monitor shows that much of Nevada, Utah, New Mexico and Arizona have the worst possible drought grade. This is labeled “exceptional drought,” and it “corresponds to an area experiencing exceptional and widespread crop and pasture losses, fire risk, and water shortages that result in water emergencies.” Some of America’s largest cities have been affected. Among them are Phoenix and Salt Lake City. According to the City of Phoenix website, the current drought problem “surpassed the worst drought in more than 110 years of official record-keeping.” In New Mexico, crops and cattle production are at risk.
One solution to drought problems is known as cloud seeding. Colorado, Utah, Wyoming, Nevada, California, New Mexico and Arizona have combined funds to use the method to create rain over the hardest-hit areas. The basic method to do this dates back to the 1940s.
The crystalline silver iodide particles have a structure similar to ice—and inside a cloud, like attracts like. Water droplets begin to cluster around the particles, freezing solid as they gather together.
The weight of the clusters makes them fall, creating snow or rain.
Among the challenges of cloud seeding is that solving the western drought likely would require hundreds of planes to fly across the skies of some of America’s largest states as measured by square miles. So, even if the process works, it may not be something that can be scaled.
In our monthly feature, Then and Now, we reveal some of the ways that planet Earth has been changing against the backdrop of a warming world. Here, we look at the effects of extreme weather on a crucial reservoir that supplies water to millions of people in northern California.
Lake Oroville plays a key role in California’s complex water delivery system.
Bidwell Marina at Lake Oroville, California
Drag button to see how extreme drought has affected lake
This 65km-square body of water north of Sacramento is the second-largest reservoir in California.
Not only does Lake Oroville store water, it helps control flooding elsewhere in the region, assists with the maintenance of water quality and boosts the health of fisheries downstream.
In 2014, more than 80% of California was in the grip of an “extreme drought”. Against this backdrop, Oroville’s capacity fell to 30% – a historic low level.
As the water level receded to hundreds of feet below normal levels, ramps and roads no longer reached the water’s edge.
More worryingly, the reservoir – when full – provided enough water for an estimated seven million households, as well as providing power for hydroelectricity facilities and irrigation for agricultural land.
The dry conditions didn’t start in 2014, however, there had been a drought for years prior to Oroville recording its historic low level.
Indeed, the US space agency’s Earth Observatory had warned that the multi-year drought was having a wider impact on the region. Among its effects was a contribution to “unusually active and destructive” fire seasons and poor yields from agricultural land.
“There is strong evidence from climate models and centuries of tree ring data that suggest about one-third to one-half of the severity of the current drought can be attributed to climate change,” observed Benjamin Cook, a climate scientist from Nasa’s Goddard Institute for Space Studies in New York.
Agency scientists added that the data suggested a “megadrought” might already be underway in this region – and that it could last for decades.
The latest update from the US Drought Monitor in December 2020, showed that much of the country’s western states were gripped by extreme or exceptional drought, with Nevada, Utah, Arizona and New Mexico, Colorado and western Texas being the worst affected.
The Drought Monitor releases maps showing the parts of the country with prolonged shortages in the water supply. It is produced jointly by the National Drought Mitigation Center (NDMC) at the University of Nebraska-Lincoln, the National Oceanic and Atmospheric Administration (Noaa), and the US Department of Agriculture (USDA).
From one extreme…
Climate change is not just about a warmer world, it also means that the planet will see more extreme environmental conditions and weather. So, for example, episodes of flooding will increase, as well as episodes of droughts.
Lake Oroville was a perfect illustration of how these extremes can threaten our existing infrastructure.
While the lake’s levels reached a historic low in 2014, the reservoir’s vast embankment dam – the tallest in the US – was pushed to breaking point in February 2017.
Communities downstream had been evacuated, with more than 100,000 people being ordered to leave their homes.
Officials were struggling to allow water to flow out of the lake because the main spillway – a structure that provides controlled releases of water – and the emergency spillway had been eroded and damaged.
Yet they had to continue sending water down the valley because the reservoir was reaching capacity and there was a sense that there could be a “catastrophic failure” in the structure.
In the space of two years, the lake went from an unprecedented low to a capacity that had not been experienced before. Water cascaded over the emergency spillways, which had not previously been required.
Traditionally, the lake was replenished by meltwater from a thawing snowpack in surrounding mountains, whose river systems fed the reservoir. June was the month when the reservoir was expected to reach its yearly maximum level.
However, in 2017, it was rain that caused the intense water flow. The reservoir had reached capacity in February, rather than the middle of the year, as usually happened.
Scientists again suggested that the event fitted into the paradigm of a warming world.
Speaking at the time to the Guardian newspaper, Prof Roger Bale, from the University of California Merced, explained: “With a warmer climate, we get these winter storms, which dump rain rather than snow.”
The United Nations Environment Programme (Unep) said that the “frequency and intensity of droughts, storms and extreme weather events are increasingly likely above 1.5C (above pre-industrial levels)”.
Failure to keep the global average temperature rise to below 1.5C, as outlined in the 2015 Paris climate agreement, is likely to result in more of the world’s reservoirs or flood defences being tested to breaking point.
This is a stark warning for world leaders, who will be gathering once again this year at the UN’s annual climate summit (COP26) – to be held in Glasgow.
The meeting, which had to be postponed by a year because of Covid, will seek to raise global ambition on tackling climate change – with a view to keeping temperature rise within the 1.5C limit.
Our Planet Then and Now will continue up to the UN climate summit in Glasgow, which is due to start in November 2021
by ARC Centre of Excellence for Climate Extremes (CLEx)
An analysis of new climate model projections by Australian researchers from the ARC Centre of Excellence for Climate Extremes shows southwestern Australia and parts of southern Australia will see longer and more intense droughts due to a lack of rainfall caused by climate change.
But Australia is not alone. Across the globe several important agricultural and forested regions in the Amazon, Mediterranean and southern Africa can expect more frequent and intense rainfall droughts. While some regions like central Europe and the boreal forest zone are projected to get wetter and suffer fewer droughts, those droughts they do get are projected to be more intense when they occur.
The research published in Geophysical Research Letters examined rainfall-based drought using the latest generation of climate models (known as CMIP6), which will inform the next IPCC assessment report on climate change.
“We found the new models produced the most robust results for future droughts to date and that the degree of the increase in drought duration and intensity was directly linked to the amount of greenhouse gases emitted into the atmosphere,” said lead author Dr. Anna Ukkola.
“There were only slight changes to the areas of drought under a mid-range emissions scenario versus a high-emissions pathway. However, the change in the magnitude of drought with a higher emissions scenario was more marked, telling us that early mitigation of greenhouse gases matters.”
Much of the earlier research into future droughts only considered changes to average rainfall as the metric to determine how droughts would alter with global warming. This often produced a highly uncertain picture.
But we also know that with climate change, rainfall is likely to become increasingly variable. Combining metrics on variability and mean rainfall, the study increased clarity around how droughts would change for some regions.
The researchers found the duration of droughts was very closely aligned to changes in the average rainfall, but the intensity of droughts was much more closely connected to the combination of average rainfall and variability. Regions with declining average rainfall like the Mediterranean, Central America and the Amazon are projected to experience longer and more frequent droughts. Meanwhile other regions, such as the boreal forests are expected to experience shorter droughts in line with increasing average rainfall.
However, the situation is different for drought intensity alone with most regions projected to experience more intense rainfall droughts due to increasing rainfall variability. Importantly, the researchers were unable to locate any region that showed a reduction in future drought intensity. Even regions with long-term increases in rainfall, such as central Europe, can expect more intense droughts as rainfall becomes more variable.
“Predicting future changes in drought is one of the greatest challenges in climate science but with this latest generation of models and the opportunity to combine different drought metrics in a more meaningful way we can gain a clearer insight into the future impacts of climate change,” said Dr. Ukkola.
“However, while these insights grow clearer with each advance, the message they deliver remains the same—the earlier we act on reducing our emissions, the less economic and social pain we will face in the future.”
Intensified by climate change, the current 20-year arid period is one of the worst on record, with wide-ranging effects
The Enterprise Bridge passes over a section of Lake Oroville that is nearly dry in 2014 in Oroville, California. The region is in the grip of a 20-year megadrought, research suggests. Photograph: Justin Sullivan/Getty Images
When Ken Pimlott began fighting US wildfires at the age of 17, they seemed to him to be a brutal but manageable natural phenomenon.
Dust bowl conditions of 1930s US now more than twice as likely to reoccur
“We had periodic [fire] sieges in the 80s, but there were breaks in between,” said Pimlott,the former head of the California department of forestry and fire protection. But no longer. “That doesn’t really happen any more. Now you can’t even blink” between fires, he said. “We’re seeing the kinds of fires we have never seen before.”
A recent study published in the journal Science helps explains why, revealing that the south-western US is in the grip of a 20-year megadrought – a period of severe aridity that is stoking fires, depleting reservoirs and putting a strain on water supplies to the states of the region.
“You see impacts everywhere, in snowpacks, reservoir levels, agriculture, groundwater and tree mortality,” said co-author Benjamin Cook, of Columbia University’s Lamont Doherty Earth Observatory. “Droughts are these amazingly disruptive events. Water sits at the foundation of everything.”
Researchers compared soil moisture records from 2000-2019 to other drought events from the past 1,200 years. They found that the current period is worse than all but one of five megadroughts identified in the record.
Unlike past megadroughts – brought on by natural fluctuations in the Earth’s climate – this current drought has been heavily influenced by human-induced climate change, “pushing what would have been a moderate drought in south-western North America into megadrought territory”, according to the study.
“Global warming has made the drought much worse than it otherwise would have been,” said Cook. “We estimate 30-50% is attributed to climate change.”
According to Nasa, 19 of the 20 warmest years on record have occurred since 2001. Climate change, if unchecked, will hit the American south-west particularly hard.
A major concern is the megadrought’s impact on water supplies in the region. It has experienced explosive growth – half of the nation’s fastest-growing states are in the south-west – made possible by elaborate river diversion projects and massive reservoirs.
Over the past two decades, drought-depleted rivers, and population growth has led to steep declines in two of the nation’s largest reservoirs, Lake Mead and Lake Powell, on which which tens of millions of people depend.
Water deliveries from the Colorado River are also being rationed this year, for the first time.
For Pimlott, this drought has manifested itself in 21st-century fires unlike any he had previously witnessed.In 2018, a fire tornado destroyed part of one northern California town, and almost the entire community of Paradise, California, was wiped out by a blaze that claimed 85 victims.
“Were seeing more intense fires, with longer durations,” he said.