Light snow began to fall around sunrise on New Year鈥檚 Eve, but as I began to clean up the debris from the previous day鈥檚 severe windstorm at my home in Boulder, Colorado, I was struck by the heaviness of the air. Not the usual moisture-laden crispness one might expect before a snowstorm, but instead there was an overwhelmingly burnt, acrid smell.

The context was immediately sobering: I was smelling the still-smoldering remnants of more than 1,000 homes that had burned in the the previous day. This same fire had raced up the canyon just down the road from our home, in perfect alignment with winds gusting more than 100 miles per hour, to bring about a catastrophic suburban firestorm in the downwind towns of Superior and Louisville.

Drone video taken Sunday morning is providing a closer look at the devastation caused by the Marshall Fire. Denver7 coordinated with the FAA, state and local authorities before and during the flight

— Denver7 News (@DenverChannel)

The fire , home to big-box stores and sprawling parking lots鈥攕tores we ourselves had patronized just minutes before the fire ignited. It jumped a six-lane freeway with ease before continuing even deeper into subdivisions out on the plains, destroying entire neighborhoods, whose residents fled by any means possible, many by car, but some on foot鈥攖he fire moved too fast for some to pull their vehicles out of the garage. I watched with horror as it roared out of the grassland and into backyards and then leaped from rooftop to rooftop.

https://twitter.com/RebeccainCO/status/1479388699997650947

As a scientist who studies the relationship between wildfires, weather, and climate鈥攁nd as a lifelong resident of the ever-flammable American West鈥擨 have more than a passing familiarity with fire. In recent years, catastrophic wildfires have become an uncomfortably familiar experience. Once seen as a distant threat, wildfire has taken center stage in the public consciousness.

And there鈥檚 good reason for this rising discourse: the American West and other areas have experienced a rapidly escalating wildfire crisis over the past decade. In California alone, 15 of the 20 most destructive fires in a century of record-keeping 鈥攈aving together cost more than 150 lives and destroyed more than 40,000 structures. More broadly, across the contiguous U.S. West, the average annual area burned by wildfire in the past 40 years.

views from Avista Hospital in Louisville today.

— BrianOnTheNet (@OriginalStalkie)

But as both and fire ecologists emphasize, the trouble isn鈥檛 actually that there鈥檚 too much fire in the West鈥攊t鈥檚 that the fires are burning with rising intensity under ambient conditions that fall increasingly far outside of historical bounds. Combine that with the of towns and urban fringes into heavily vegetated areas (known as the wildland-urban interface, or WUI), and it becomes easier to understand the problem at hand.

We鈥檝e returned to the Louisville neighborhood where we spent the afternoon watching firefighters try to hold the Marshall Fire at McCaslin Blvd. This is looking south over Harper Lake where homes are burning from one end of the neighborhood to the other.

— Kyle Clark (@KyleClark)

I often describe the wildfire problem as a stemming from the simultaneous escalation in risk brought about by three key factors. The first of these is the unfortunate legacy of forest and fire management policies from the 20th century; natural fires, which would have thinned forest understory and reduced vegetation density, known as 鈥渇uel loading,鈥� were continuously suppressed, across most of the West鈥檚 forests. The second factor is the rapid expansion of populated areas into wildfire risk zones, whether in the form of scattered homes deep in the woods or sprawling subdivisions on the margins of rural vegetated tracts of land, which puts far more people and structures potentially in harm鈥檚 way when a fire comes along. The third factor is climate change, which has length and caused substantial drying of vegetation, that fires can attain.

The first two factors are somewhat conditional: historical forest fire suppression and increased fuel loading are mostly relevant in forests, after all, and many Western fires (like the Marshall Fire) burn in vegetation types other than forest; the WUI has not expanded everywhere, and scientists are still observing well away from population centers. Climate change, on the other hand, is decidedly more pervasive: it鈥檚 happening everywhere, and no part of the West remains untouched. Thus, the relative importance of each of these three factors varies from fire to fire, depending on the local geographical, ecological, and climate context.

In the case of the Marshall Fire, it鈥檚 pretty clear that historical forest management was not to blame, as this was by no means a forest fire. It ignited in a brushy landscape scattered through the vegetation. In its first 30 minutes, this vegetation fire consumed mainly brush and grass, along with a handful of structures. But soon thereafter, pushed by violent wind gusts of 90 to sometimes more than 100 miles per hour, the fire emerged into a truly suburban landscape. It became, effectively, a self-sustaining urban conflagration鈥攂urning from structure to structure and fueled more by the vegetation in backyards, road medians, and city parks than by anything that could be reasonably be considered wildland. Most of the structures that burned had been built in the past 30 years; previously, much of this area had been part of the Denver metro area鈥檚 extensive Great Plains grassland that has largely disappeared due rapid development. This expanded suburban footprint is clearly a major part of the story.

One of the more sobering videos taken by BPD Patrol off S. Marshall Rd. in Superior on Thursday afternoon during the height of the fire. First responders from all over the Denver Metro area rushed to help with evacs and traffic control. 鈦︹仼

— Broomfield Police (@BroomfieldPD)

So, what about climate change? Well, the data show that the six months leading up to the fire were singularly the along the Colorado Front Range and among the driest. I saw this firsthand: autumn 2021 was eerily balmy in Boulder, with temperatures often into the 60s and overnight lows well above freezing most of the time鈥攃onditions more befitting of coastal California than above 5,000 feet elevation in Colorado. The cumulative vapor pressure deficit鈥攁 measure of atmospheric 鈥渢hirstiness鈥� that is strongly related to vegetation dryness and wildfire behavior鈥� prior to the fire鈥檚 ignition. That unusual heat and dryness followed what was actually a remarkably wet spring, a sequence of events that allowed for prodigious growth of brush and grass earlier in the year, then subsequently for months-long dehydration of all that new growth that provided fuel for the fire. , as well as and increasing in some parts of the West, have been repeatedly linked to climate change. In other words: long-term climate trends in summer and autumn helped establish the preconditions necessary for a fast-moving winter fire.

https://twitter.com/GRDenver/status/1476757009122873351

Then there is the question of the winds themselves. Strong downslope gusts are actually rather common along the Front Range in winter, though this event was particularly violent. (One nearby gust was clocked at 115 miles per hour.) There isn鈥檛 any reason to believe the winds themselves have been accelerated by climate change, although there is little research on the topic. But climate change has dramatically into erstwhile 鈥渟houlder seasons鈥� in the spring and autumn鈥攁nd, increasingly, into winter as well. As I watched the Marshall Fire in late December 2021, I couldn鈥檛 help but reflect on a similar experience I had just over one year earlier, in mid-October 2020, when I witnessed the fast-moving roar out of the foothills just north of Boulder and wipe out dozens of homes. Furious downslope winds were also the proximal culprit in that disaster, but the unusually dry vegetation conditions facilitated the fire鈥檚 rapid spread in the first place. At the time, my colleagues and I thought it quite late in the calendar year to see a fire of that magnitude in this part of the world. And now, in 2021, we鈥檙e having the same conversation yet again鈥攅xcept this time it鈥檚 in the heart of winter.

When it comes to meeting the challenge of escalating fire catastrophes amid overstocked forests, an ever-expanding urban interface, and worsening climate change, there are no easy answers. Because the underlying causes are complex and multifactorial, so must be the solutions: there simply is no silver bullet. Many folks would rather there be a singular villain鈥攂ut the reality is that all of these factors are critically important to varying degrees. Making toward mitigating this crisis means addressing each component head on: using to reduce and improve ecosystem resilience; reimagining how we design neighborhoods and to make them more fire resistant; and, of course, as quickly as possible to eventually halt climate change. None of this will be easy, but given that the alternative is an ever-increasing risk of catastrophic fires, we simply can鈥檛 afford not to act.

Daniel Swain is a climate scientist with joint positions in , the , and the . He can be found on Twitter at .听

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It鈥檚 the middle of October, and the world is already witnessing the strongest El Ni帽o since the record-setting 1997-1998 event, which brought huge shifts in global weather patterns and wrought havoc all around the Pacific.

A consensus of ocean and climate models suggests that El Ni帽o will continue to strengthen over the next couple of months before peaking sometime this winter. In fact, the present event is already among the top three ever recorded in terms of its warming effect on ocean temperatures (the most direct听indicator of听El听Ni帽o's power), and it鈥檚 even possible that this one could steal the all-time title from the 鈥�97-鈥�98 event, becoming the most powerful in modern history.

Last year鈥檚 hotly hyped non-event has come to be known as the 鈥淕reat El Ni帽o Fizzle,鈥� since early excitement surrounding the development of strong warming in the Pacific quickly faded away in the summer of 2014 when the ocean and atmosphere didn鈥檛 cooperate. In early 2015, when real-world observations and climate models once again started to suggest a high likelihood of a substantial El Ni帽o event, excitement was muted at first by the previous El Ni帽o鈥檚 failure to thrive.

But this year, the atmosphere and ocean are in synch. Trade winds have slackened, a nearly continuous parade of tropical cyclones has marched westward across the Pacific, and rapid warming is ongoing in the eastern tropics鈥攖elltale signs that El Ni帽o is already exerting a heavy influence upon Pacific climate.

El Ni帽o is an oceanic phenomenon characterized by warming of the eastern tropical Pacific Ocean. This unusual ocean warming, which happens every two-to-seven years on average, disrupts the typical 鈥渨arm west/cool east鈥� temperature differential across the tropical Pacific. These perturbed ocean patterns weaken prevailing east-to-west trade winds, and eventually affect weather patterns all around the world. While El Ni帽o (and its sister, La Ni帽a, which is characterized by tropical ocean cooling) tends to be associated with specific weather impacts in certain regions, no two El Ni帽os are alike鈥攁nd neither are their effects on weather.

That said, there are some historic big-picture patterns emerging that听may give us some insights into what kind of weather听we鈥檒l see this winter up and down the drought-stricken West.听

1. California: Wet, But Not Snowy

Many Californians may be wondering: What does a massive El Ni帽o event mean in the midst of a record drought? The answer is a bit of a mixed bag.听

This year鈥檚 powerful El Ni帽o will probably bring above average precipitation during the core rainy season months of January, February, and March. This prediction is supported by both historical records and by today鈥檚 forecasting models, which suggest a persistently stormy pattern will develop by January. But it鈥檚 important to remember that even a very wet winter won鈥檛 end California鈥檚 drought. Heavy precipitation would bring an increased risk of flooding and mudslides ( near Los Angeles)鈥攅specially in areas scorched by this summer鈥檚 ferocious wildfires. But it does appear that at least some drought relief鈥攈owever modest鈥攊s on the way.

The bad news: record warm ocean temperatures off the coast will probably keep things much warmer than average for most of the coming winter. This means that the elevations at which water freezes in the Sierra Nevada will once again most likely be well above average, and prospects for a substantial snowpack are not great, despite all the extra water. (That鈥檚 not good news for California鈥檚 long-term reservoir storage, which is heavily dependent on snowmelt.) At the highest elevations, though, it鈥檚 plausible that conditions will still be cold enough for snow, and given an increased likelihood of heavy precipitation, that could mean some fairly prodigious snow totals for those few ski resorts lucky enough to have slopes above 8,000 feet or 9,000 feet.

2. The Pacific Northwest: Warm and Dry

Oregon and Washington are also enduring a severe drought鈥攎ostly due to warm temperatures. Despite near average precipitation last winter, snowpack in the Cascades was at record-low levels due to the vast majority of precipitation falling as rain rather than snow. Unfortunately, it appears that drought conditions in the Northwest will probably worsen this winter, as it鈥檚 increasingly likely that below-average precipitation and above-average temperatures will prevail.

What does this mean for snow? Well, the good news is that the coming winter will probably bring more snow than last year even if the overall totals are underwhelming. But that鈥檚 more of a testament to just how little snow accumulated last year than an expectation of favorable snow conditions this year. The overall prognosis up north is similar to California鈥檚: higher-elevation snow lines may leave the lower mountains snow-free, but accumulations at the highest elevations may be larger than last year鈥檚 abysmal amount. Here again, alpine skiers may fare better than water managers hoping for substantial spring and summer snowmelt next year.听

3. Rocky Mountain States: Snowy in the South

Further inland, Rocky Mountain states may see conditions comparable to those in the Northwest and California鈥攁nd, similarly, the conditions will vary from region to region.

In the north, fewer surges of cold air from the Arctic may keep temperatures warmer than average. The Northern Rockies may see similar conditions to those in the Pacific Northwest: due to a southward-shifted storm track, rain and snow may be below average.听

The Southern Rockies, however, will see very different weather. With an enhanced storm track, precipitation will most likely be above average. Due to increased cloudiness and storminess, temperatures in the south will probably not be as far above average as they will be elsewhere in the West. In fact, during the core winter months, conditions may even bit a bit on the cool side. This may open the door for some substantial accumulations of snow, which would be good news both for skiers and the tens of millions of people who depend on the drought-stricken Colorado River watershed, which has been in the grips of a protracted drought for even longer than California.

The post How El Ni帽o Will Affect the West this Winter appeared first on 国产吃瓜黑料 Online.

Why has it been so warm and dry out West? That鈥檚 a question just about everyone left of听the Rockies has puzzled over these past few years. As the eastern U.S. has found itself facing the brunt of 鈥淪nowpocalypses,鈥� 鈥淪nowmageddons,鈥� and other remarkable winter-weather events, historically verdant states like California and Colorado have been slowly fading into a worrisome shade of brown for more than a decade.

Rainfall and snowpack in the West have dwindled to record lows, but those are merely symptoms of a larger, persistent atmospheric configuration that has become essentially stuck in place over the past several years. Because of that, it鈥檚 worth looking听to the skies for clues about the origins of the West's water woes. Here鈥檚 a (literal) top-down approach to understanding what is causing the drought in the West:

The Rise of the 鈥淩idiculously Resilient Ridge鈥�

California's climate is typically characterized by a reliable annual cycle of precipitation, with predictably wet winters and almost invariably dry summers. A relatively small handful of winter storms during the typical October-to-May 鈥渨et season鈥� are responsible for a majority of the rain and snow that falls in the Golden State in any given year. But this parade of storms has been interrupted for the past four years by听an atmospheric anomaly I call the 鈥溾�� (or the Triple R).

The Triple R is a region of unusually high atmopsheric听pressure hanging around the northeastern Pacific Ocean. It听prevents听the Pacific jet stream and associated stormy weather out of the Arctic from traveling to much of the West Coast. Storms that otherwise might have hit San Francisco or Los Angeles are instead re-directed to Anchorage and Vancouver, bringing even rainier conditions to already wet places and leaving California dry. Other parts of the American Southwest have experienced dry conditions as a consequence of the Triple R, but three-year precipitation shortfalls are currently much larger in California than anywhere else in the West.

The Great Western Snow Drought of 2015

Striking photographs of snowless mountain peaks in the heart of winter鈥攁nd recent news that the amount of water stored in California鈥檚 mountain snowpack is almost nonexistent鈥攈ave highlighted the role of high temperatures in amplifying the severity of existing drought conditions. But these incredibly warm temperatures have not been confined to California: unprecedented warmth has led to extremely low snowpack conditions across nearly the entire West this year.

Even in places that have received plenty of precipitation鈥攍ike the Cascades of Washington and Oregon鈥攊t's听fallen as rain rather than snow, leaving many mountain slopes bare even after winter storms roll through. At the same time, prolonged dry spells and extended stretches of well-above-freezing high-elevation temperatures in between storms听have allowed what little snow has fallen to melt during the heart of winter鈥攑recisely the time of year when the white stuff should have been accumulating.

An increasingly big part of the Western temperature story is the extraordinarily warm Pacific Ocean. A region of unusually high water temperatures in the far northeastern Pacific鈥攁ffectionately nicknamed 鈥溾�� by oceanographers鈥攈ave translated into warmer, wetter storms moving in off the Pacific, bringing warmer rain at very high elevations all up and down the Pacific Coast.听

Why Is the Triple R So Persistent?

The short answer: We don鈥檛 have a clear answer yet.

It appears increasingly likely, though, that an unusually warm western tropical Pacific Ocean鈥攁s far away as the waters east of Indonesia and the Philippines鈥攊s playing a big role. Powerful tropical thunderstorms, driven by anomalously warm ocean water, can pump vast amounts of heat high into the tropical atmosphere, where it meets with cooler air from the north. This convergence strengthens the high-altitude wind, known as the “jet stream,”听that helps to guide the trajectory听of storms across the Pacific.听But an unusual injection of jet stream energy can also lead to thousand-mile-wide kinks in the jet stream's west-to-east flow and redirect storms away form the U.S. West Coast.听Such conditions听have allowed the Triple R to develop and maintain its stability.

It鈥檚 also possible that the rapid loss of Arctic ice and snow is having an effect on the Pacific jet stream at certain times of year. Just as unusually warm ocean water in the tropics can increase temperature contrasts in the atmosphere above, so too can unusually warm ocean waters in the Arctic (caused by a lack of sea ice) or unusually cold land temperatures (caused by abundant Siberian snowfall), which in turn听affects the path听of weather systems across the Pacific. And it just so happens that the changes we鈥檝e observed in the high-latitudes may be in sync听with oceanic oscillations that favor a big, circuitous loop in the jet stream near western North America鈥攐ne highly reminiscent of the Triple R.

To make things even more complicated, there鈥檚 growing evidence that all of these possible influencing factors are being affected by global warming. We already know that the American West has warmed considerably over the past century, which has contributed to the observed loss of winter and spring snowpack in many regions and increased the overall risk of drought in California. But the degree to which long-term changes in climate are influencing the likelihood of seeing warm听winters like we鈥檝e experienced recently remains a fascinating open question鈥攐ne to which scientists are actively seeking an answer.听

A Brief Look Ahead

While there鈥檚 currently some hope that a developing El Ni帽o event in the Pacific Ocean might bring partial relief to the West Coast toward the end of 2015, that possibility remains highly speculative at the moment. One thing we do know with certainty, though, is that a long, dry summer awaits California and the rest of the West.听And in spite of (and a record for the wettest month in Colorado)听there are widespread expectations that 2015 could feature one of the worst wildfire seasons in living memory鈥攍argely on account of ongoing severe drought conditions and the astonishing lack of mountain snowpack in 2015. So in the meantime, at least, the legacy of the Triple R lives on.

Daniel Swain is a PhD student in the Department of听Earth System Science program at Stanford University. He authors听the blog .听

The post A Weather Scientist Explains the Drought in the West appeared first on 国产吃瓜黑料 Online.