The largest and most intense drought in years is engulfing the West and threatens to grow larger and more severe in the coming months.

The drought has already been a major contributor to record wildfire activity in California and Colorado. Its continuation could also deplete rivers, stifle crops and eventually drain water supplies in some Western states.

Nationwide, drought has expanded to its greatest areal coverage since 2013; 72.5 million people are in areas affected by drought. More than one-third of the West is in “extreme” or “exceptional” drought, the two most severe categories, according to the federal government’s U.S. Drought Monitor.

In its winter outlook issued last week, the National Oceanic and Atmospheric Administration (NOAA) cautioned drought conditions are expected to persist or worsen over large parts of the West during the December through February period, and expand farther east into the central United States.

Dry conditions have fed devastating fire season

In recent months, drought has surged to extreme levels along parts of the West Coast, including Northern California, much of Oregon and the Cascades in Washington.

Soils have been sapped of moisture, with intense heat waves drying out vegetation even further. This has led to rampant and sometimes explosive wildfire growth.

Elevated temperatures have further helped to dry out the soil, exacerbating the drought and making fire weather conditions even more hazardous. California, for example, had its warmest August on record, and a severe heat wave in early September led to a deadly spate of wildfires.

In Colorado, wildfires continue to rage along the Front Range, with evacuations west of Fort Collins and northwest of Boulder. The Cameron Peak Fire, which has torched more than 200,000 acres, is now the largest wildfire in Colorado history, and the CalWood Fire became Boulder County’s largest fire on record when it exploded in size over the weekend. That fire has burned at least 26 homes, though the toll is expected to increase.

There is no precedent for wildfires this severe igniting so late in the season in the Centennial State. It’s no coincidence that the entirety of Colorado is experiencing a drought for the first time since 2013. Fifty-nine percent of the state is enduring an extreme drought or worse.

2020 has been a particularly bad year for wildfires, obliterating records in California with more than 4.1 million acres scorched. This is more than twice the acreage burned during the previous record wildfire season.

An environment already parched from a lackluster monsoon

The Four Corners region is perhaps the one hit hardest, where prolonged, intense dryness has led to “exceptional drought.”

In New Mexico, an area one and a half times the size of the state of Connecticut is listed by the U.S. Drought Monitor as being in extreme drought. This includes Los Alamos and Santa Fe. Officials have noticed a dramatic decline in river flow rate feeding many aquifers, though there are no immediate drinking water supply concerns. The Drought Monitor includes the observation that “vegetation and native trees are dying” in parts of the state.

An exceptionally weak monsoon has been a major contributor to the ongoing drought in the Southwest.

The term “monsoon” describes a seasonal wind shift, which transports moisture from the Gulf of Mexico, Gulf of California, and the eastern Pacific to the Desert Southwest beginning in June and continuing into the early fall.

But in 2020, the monsoon largely failed to deliver, leaving drought-stricken areas with even greater rainfall deficits.

In August, for example, Santa Fe picked up just one one-hundredth of an inch of rain. It averages 2.6 inches for the month. Since the start of the year, the city has had 5.44 inches of precipitation, less than half the 11.5 inches it would typically have by now.

It’s the second dud monsoon season in a row.

“Last year, the 2019 monsoon season, it wasn’t that great. … It was kind of a failure,” said Royce Fontenot, senior service hydrologist at the National Weather Service in Albuquerque. “And this year, we had what we jokingly called the ‘non-soon.’ ”

That’s left a 34-mile stretch of the Rio Grande flowing discontinuously, Fontenon explained. He said that’s not terribly rare but only happens during serious drought.

A large percentage of New Mexico’s rainfall — in some places more than half — comes from the monsoon.

“We need that monsoonal precipitation for effective runoff just as much as we need the snowpack.”

Fontenon said that the rangeland in eastern New Mexico is suffering heavily, bringing shades of a drought early in the decade that plagued area farmers between 2011 and 2013.

Nearby in Arizona, Tucson hasn’t seen a drop of rain since August. Since the start of May, less than two inches has fallen. The year as a whole is 60 percent below average on rainfall.

Even farther north, the deficit has hit the Rockies and Intermountain West particularly hard. Grand Junction, Colo., has only seen 4.09 inches of rain this year; by now it should be in the double digits. Salt Lake City is at 7.86 inches. That’s five inches below average.

Extreme drought has also snaked its way into Wyoming, while moderate drought blankets most of Idaho and Montana.

The drought will only worsen

Forecasters at NOAA say that with a developing La Niña event in the Pacific Ocean, drought is likely to prevail and potentially worsen through the winter over large areas of the West.

La Niña conditions feature cooler than average ocean temperatures in the central and eastern equatorial tropical Pacific Ocean, with associated changes in winds and rainfall that can affect weather patterns far from the tropics. Such events can help shunt the jet stream well northward toward the Aleutians and Pacific Northwest, carrying moisture-laden storm systems north of California and far from the Desert Southwest.

During a La Niña pattern, drier-than-average conditions are typical across much of the southern United States and Great Plains, which is reflected in NOAA’s winter outlook, released Thursday.

The National Weather Service in Albuquerque reviewed winter precipitation departures from average from the past seven La Niña events and found that winter precipitation in many areas was a quarter to a third below the long-term average.

Little relief in sight for most

There does appear to be some relief in sight for parts of the drought-stricken areas of the Pacific Northwest, although it will take many storm systems to bring the region out of its precipitation deficit.

The upcoming pattern favors some storminess and precipitation for portions of the Northern Tier, northern Rockies and Pacific Northwest. The first waves of light to moderate rain may arrive in western regions late this weekend.

This pattern of storminess is fairly characteristic of La Niña events and is the primary reason NOAA’s latest drought outlook calls for improvement in the Pacific Northwest.

But looking ahead, little to no wet weather whatsoever is expected in the Southwest, southern California, or the Four Corners region. And the drought will probably continue, if not intensify.

Climate change’s role

Human-caused climate change is increasing the likelihood of precipitation extremes on both ends of the scale, including droughts as well as heavy rainfall events and resulting floods. Studies consistently show that as the Southwest warms, the odds of drought are increasing.

According to the Federal National Climate Assessment in 2018, climate change intensified the severe drought in California and is worsening drought in the Colorado River Basin. Part of the reasons for this is that climate change makes such droughts hotter than they might’ve been just a few decades ago, which draws more moisture out of soils and vegetation, thereby worsening the drought in a positive feedback loop.

“Higher temperatures sharply increase the risk of megadroughts — dry periods lasting 10 years or more,” the report stated. Climate projections show large reductions in snowpack, a key source of water during the spring and summer months, in the Southwest.

A recent study published in the journal Science found that the Southwest may already be in the midst of the first human-caused megadrought in at least 1,200 years, which began in the year 2000.

Andrew Freedman and Jason Samenow contributed to this report.