LAS VEGAS (KLAS) — Snowpack levels crucial to water supplies in the Colorado River basin have been rising over the past week as storms hit the Rocky Mountains.

Dec. 27 measurements of 102% snowpack in the region — just above normal — had risen to 142% as of today (Jan. 3) in the Upper Colorado River Basin.

That week-to-week change is good news but demonstrates the volatility of snowpack levels. Just as rainfall makes little to no impact on the level of Lake Mead, snowpack levels in early January shouldn’t be seen as a sign that a few snowstorms will erase years of drought, experts say.

Current snowpack data reported by the U.S. Bureau of Reclamation.

Kyle Roerink, executive director of the conservation group Great Basin Water Network, said long-term forecasts showed river flows expected to be about 87% between now and April.

“November inflows into Lake Powell and other upstream reservoirs that are important for Lake Mead operations were all below average,” he said. “December estimates were expected to be less than November — with January and February hovering in the same territory, meaning that we are in need of some real big precipitation events.”

Atmospheric river

The “atmospheric river” conditions that are feeding moisture into the Colorado mountains are certainly helping. That pattern was expected to end sometime this week.

“A good winter that exceeds 100% of normal will not solve the problem. It may stave it off for a year or two,” Roerink said.

Snow is seen on a Chevrolet C10 pickup truck along U.S. Route 50 in South Lake Tahoe Calif., Friday, Dec. 30, 2022. (Stephen Lam/San Francisco Chronicle via AP)

Currently, snowpack conditions throughout the basin are above normal. Mountains that feed the headwaters of the Colorado River are at 129% of normal. The highest levels are in Utah, where mountains that feed the Green River are at 180% of normal snowpack and the Lower San Juan region is at 175% of normal.

But that might mean nothing by the time it really matters. The important time for snowpack measurements is in April and May. Until we see those snowpack levels, we won’t really know if it was a good winter or not.

A sports utility vehicle drives along a road lined with trees scarred by the 2021 Caldor Fire at Sierra-at-Tahoe in Twin Bridges, Calif., Friday, Dec. 30, 2022. (Stephen Lam/San Francisco Chronicle via AP)

Redefining normal

The long-term impact of the drought has brought a “new normal” to the Colorado River basin. Hydrologists — water scientists — say that snowpack levels don’t mean what they did before the drought.

Years of heat and low precipitation have essentially dried out the ground, and moisture from the snowpack has to restore that moisture as the snow melts each year. Hydrologists have found that means a significant cut in the amount of water that actually makes it downstream.

How much? Roerink describes it as “an inexact science.”

“From what we’ve seen in tributaries in La Niña Conditions, the percentage of runoff will be somewhere in the ballpark of 10-20% less than the percentage of snowpack.”

See how the snowpack levels have changed over the past week:

A report in late October indicated a strong start to the “water year,” which begins on Oct. 1 each year. Snowpack in October was at 229% of normal.

Another note on “normal:” The established method of calculating “normal” snowpack is based on the past 30 years of data. And more than 20 of those years fall within the “megadrought” that is currently running its course. So “normal” is a relative term.

Climate change

And climate change’s effects are now being quantified as more data becomes available.

“In effect, temperature is opening up a gap between precipitation and streamflow,” according to Jeff Lukas of the Western Water Assessment, a team of scientists from the University of Colorado, the University of Utah and the University of Wyoming.

“In the past 40 years, a warming trend of about 2 degrees Fahrenheit has discernably impacted basin hydrology. This regional warming, like that at broader scales, has been linked to human causes,” Lukas said in summarizing a study of hydrology in the Colorado River basin released in 2000.

“Since 2000, a period of slightly-below normal precipitation in the basin has been exacerbated by higher temperatures leading to even lower snowpacks, earlier runoff and lower streamflows than would have occurred in the absence of warming,” he said.

“Several recent studies show that 20-50% of the observed cumulative streamflow deficit since 2000 at Lee’s Ferry is due to the warmer temperatures.”

A Wiki created in 2022 now provides “a web-based clearinghouse for scientific and technical information relevant to the Colorado River Basin and the management of its water resources and related natural resources.”