La Niña winter could mean dry winter for southern Colorado, but conditions better than this time last year.
Oct 6, 2021
Drought conditions have eased up a bit from this time last year, but as the calendar turns on Colorado’s water year, worries about a dry winter still loom, the state’s assistant climatologist says.
That’s not to say Colorado isn’t parched. Most of the state remains in drought, including the Eastern Plains, which spent much of the summer drought-free.
Now, with a La Niña weather pattern shaping up, the southern part of the state in particular could see drought conditions worsen, said Becky Bolinger, the state’s assistant climatologist.
The new water year — the period used to observe Colorado’s snowpack — began on Oct. 1, capping a year that saw extremes in both drought and precipitation, Bolinger said.
“It was a real roller coaster of a water year,” Bolinger said.
A water year is a bit like a fiscal year, Bolinger said. It’s a period that starts when water begins to accumulate in the form of snow in the Colorado high country, which typically occurs in October, and ends when that cycle runs its course.
Snowpack makes up the bulk of Colorado’s water supply, which melts off in the spring and is stored in reservoirs.
Though there is uncertainty in weather models, Bolinger said Colorado is likely in for a La Niña winter this year, a weather pattern that could mean paltry snowpack in the southern part of the state, with the possibility of decent snowpack in the northern part.
“La Niña has northern and southern components, but where those line up isn’t precise,” she said. “It tilts the odds toward less snow in the southern mountains, and maybe a better chance for more snow in the northern mountains.”
Colorado is off to a better start to the 2021-22 water year than the year before, Bolinger said.
The 2020-21 water year began in the midst of a catastrophic wildfire season that stretched far later into the autumn than normal, she said. The East Troublesome fire, which grew to nearly 200,000 acres in northern Colorado, didn’t begin until Oct. 14, two weeks into the new water year.
At this time last year, 100% of the state was experiencing some level of drought, according to the U.S. Drought Monitor. This year, about 87% of the state is in some level of drought, with only patches of the Front Range, Eastern Plains and a portion of south-central Colorado considered drought-free. In Colorado’s northwest corner, an area of “exceptional drought” — the Drought Monitor’s highest rating — persists.
Heading into last summer, more than half of Colorado, mostly east of the Continental Divide, was free of drought.
The Western Slope spent much of the past water year locked in a drought so bad many ranchers were forced to sell off cattle, water managers closed long stretches of the Colorado and Yampa rivers to fishing, and federal officials rounded up hundreds of wild horses they say faced starvation as forage dried up.
The difference was caused by where the jet stream was positioned last winter and spring, Bolinger said. The drought on the Western Slope was exacerbated by exceptionally dry soils that quickly sucked up the snowpack that accumulated over the winter.
“We had a moisture deficit to make up, and even an average snowpack year wouldn’t have done it,” she said.
Snowpack on the east side of the divide wasn’t bad. Both the South Platte and Arkansas River basins topped out at 102% of their average peak, according to the National Resource Conservation Service. The Rio Grande basin, which covers the San Luis Valley, topped out at 103% of its average peak.
The story was much different on the Western Slope. The Yampa River basin topped out at 86% of its average peak. The Colorado River basin topped out at 87%, and the Dolores River basin that encompasses much of southwestern Colorado hit 85% of its peak.
“That means we’re starting this water year with reservoirs well below where they should be,” Bolinger said.
Can the reservoirs refill?
Forecasters are concerned about refilling reservoirs drained this year. Blue Mesa Reservoir near Gunnison was at just 29% of capacity, or 40% of average, on Oct. 4, according to the Natural Resources Conservation Service. That’s down from 37% of capacity at the beginning of September, after federal water managers kicked off plans to send 36,000 acre-feet of water downstream to Lake Powell straddling the Arizona/Utah border.
Blue Mesa is one of three Upper Colorado Basin pools tapped to bolster Lake Powell to preserve Glen Canyon Dam’s hydroelectric generating capacity amid dire drought conditions.
Vallecito Reservoir near Durango is at just 19% of capacity, while Pueblo Reservoir, on the other side of the Continental Divide, is at 51%.
The numbers are a little better.In the northern part of the state. Lake Granby, which serves northern Colorado communities, was at 71% of capacity on Oct. 4. Horsetooth Reservoir near Fort Collins was at 79%, and Cheesman Reservoir, which serves Denver Water customers, was at 97%.
Monsoon rains brought helped relieve some of the soil moisture deficit in western Colorado, Bolinger said, though they also brought another problem: torrential downpours hit burn scars left by the 2020 wildfires, where superheated fire activity left soils unable to absorb sufficient moisture, causing devastating mudslides.
A series of mudslides originating above Glenwood Canyon closed Interstate 70 on several occasions in July, culminating in what the National Weather Service called a 500-year storm event at the end of July, causing a mudslide that left I-70 closed for two weeks.
Colorado’s drought conditions are part of a trend stretching back to the turn of the 21st century, Bolinger said, and are being made worse by climate change.
Though the state will still see wetter-than-average stretches, as happened in the 2018-19 water year, Bolinger said the overall trend is likely to be toward a hotter, dryer climate.
“The severity of our droughts is increasingly temperature-driven,” Bolinger said. “It’s not just about a deficit of precipitation.”
Increased temperatures cause a climb in “evaporative demand,” or how much moisture the atmosphere sucks up from soils, meaning even above-average snowpack years will have trouble refilling reservoirs.
The bright side is that Colorado, with its spine of high mountains that collect snow, can recover from droughts more quickly than lower elevations where snow is far more ephemeral.
“It doesn’t take a miracle to get drought relief in our state, but as we step back and look at the bigger picture of the western United States, I don’t envision we’ll see much recovery of reservoirs like Lake Powell,” Bolinger said.
While state and federal water managers hash out how to deal with dwindling river flows and reservoirs, Bolinger said individuals can work on making their homes and communities more drought-resilient by minimizing water use with more native grasses and trees.
“We don’t have to talk about completely xeriscaping, like Phoenix and Las Vegas, but native plants can really cut down a home or town’s water use.”
In the meantime, Bolinger said she’s hoping for robust snowpack — at least in the northern part of the state.