LAS VEGAS (KLAS) — Snowpack levels in the Upper Colorado River Basin have improved over the past two weeks, fueled by an “atmospheric river” carrying moisture from the Pacific Ocean.
It’s a good sign after recent dry years, but certainly not a guarantee that conditions will continue until April when snowpack usually reaches its peak levels.
Since Jan. 3, snowpack has grown another 11%, according to data provided by the U.S. Bureau of Reclamation’s website. Levels that were at 142% of average early this month are now at 153% of average. The map below shows precipitation and snowpack information for the Upper Colorado River Basin, the source of water that flows down the river to the two largest reservoirs in the country: Lake Powell and Lake Mead.
Water content of snow
And there are more signs that climate scientists point to as evidence that the snowpack will help after a record dry year.
Karl Rittger, a researcher at the Institute of Arctic and Alpine Research at the University of Colorado, said Wednesday that “snow water equivalent” (SWE) data shows that levels are at 140% or greater in most of the basin. Mountains in southern Wyoming and northern New Mexico are lagging, between 80% and 100% of average.
The water produced by snowmelt feeds the two biggest reservoirs in the country: Lake Powell and Lake Mead. But it’s important for snowpack to continue growing until springtime — it shouldn’t be melting during winter and early spring.
Also, observations from the National Snow and Ice Data Center (NSIDC) indicate the snowpack continues to reflect solar energy.
Rittger explained: “So, the snow isn’t absorbing a lot of solar energy, which really contributes to the bulk of melting snow.” That could mean it will last while more storms build snowpack even higher through winter and into the spring. As dust accumulates on the surface of snow, it increases the rate that snow melts as more solar energy is absorbed. Fresh snow reflects light.
Rittger’s Snow Today website (www.nsidc.org/snow-today) shows SWE measurements overlaid on snow cover maps.
And snow is covering a lot more ground than last year. An article on the Snow Today site says snow cover at the end of January last year was nearly the lowest in the 22 years that data has been collected.
“All of this together,” Rittger said, “means atmospheric rivers are making an impact in the Upper Colorado.”
Lake Mead is currently at 1,045.8 feet — about 5 feet above where it was near the end of July (1,040.6 feet). It’s about 21 feet below where it was a year ago today. Lake levels are expressed as altitudes — the number of feet the lake’s surface is above sea level — not as depths.
Previous measurements
See how the snowpack levels have changed since Jan. 3, dropping to 139% of normal on Jan. 9 and then climbing:
Another website that monitors SWE data — snowpack.water-data.com — reports snowpack at 139.76% of normal on Jan. 19, and 75.41% of the average April 6 peak snowpack level.
Climate change effects
Other areas of climate science have also advanced during the drought years.
“The average flow of the Colorado River has already declined nearly 20% since 2000, with half of that attributable to rising temperatures,” according to The Nature Conservancy. “Temperatures in the basin are predicted to rise another 2-5 degrees Fahrenheit by 2050, which could reduce river flows by another 10 to 40%.”
Snowpack is volatile. Near the end of October, snowpack levels were at 229% of normal. Warm days could change the picture in a hurry.
“Extensive warm and dry periods during January and February could trigger earlier and smaller runoffs, exacerbate the soil-moisture deficit, and limit groundwater recharge,” according to Kyle Roerink of the conservation group Great Basin Water Network. “A good winter that exceeds 100% of normal will not solve the problem. It may stave it off for a year or two.”
And snowpack won’t necessarily translate into normal runoff after years of drought.
“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. It is an inexact science. But I think it is important to note that a 100 percent snowpack does not equal 100 percent runoff,” Roerink said.