From Climate Central:
Even with the heavier snow in parts of the West last week, the snowpack depth measured at the end of the season for the West as a whole is below normal. It is a shift from last year’s snow surplus but is more representative of the long-term trend; 2011 and 2017 were the only two years this decade in which the snowpack was above normal. The Northwest had a favorable snowfall season, but drought returned to California after last year’s wet season, with extreme drought now extending eastward from California to the Southern Plains. Arizona and New Mexico are particularly dry, with each state receiving less than half of its normal snowfall through the end of March.
As the world continues to warm from increased concentrations of greenhouse gases in the atmosphere, early spring snowpack has been trending downward. In addition to more intense droughts from decreased snowpack, warming winters mean that the percentage of winter precipitation that falls as snow is decreasing, which also contributes to the snowpack decline.
While the West has a long history of droughts and wet periods, the droughts have been getting more intense over the past century. This has led to a depletion of deeper groundwater, which takes more than a single wet season to recover. According to the National Environmental Education Foundation, water managers in 40 states expect water shortages in some parts of their states in the next 10 years.
From The Sopris Sun (Will Grandbois):
The Roaring Fork Conservancy’s weekly snowpack report has the watershed as a whole at 75 percent of normal — better than the southwestern part of the state but not as robust as parts of northern Colorado and the Front Range. According to Education & Outreach Coordinator Liza Mitchell, area snowpack usually peaks around April 1, but that’s just a milestone, not a point of no return.
“We’re going to have above average years and we’re going to have below average years,” she said. “While there’s definitely concern, there is sort of a silver lining in that we’re coming off of two years that were well above average… Our reservoirs are like savings accounts for a not-so-rainy summer. When it becomes really bad is when we have back-to-back years like this.”
The Conservancy and local partners have also put effort into programs that will help residents, ranchers and wildlife weather tough years. The Crystal River Management Plan, for instance, makes it possible for irrigators to reduce their usage without losing their water rights.
“The only certainty is that things will become more unpredictable, so we’re trying to set ourselves and the river up for success — be proactive instead of reactive,” Mitchell said. “Each and every one of us is a water user and therefore water diverter.”
From Aspen Journalism (Brent Gardner-Smith):
For much of the winter, the snowpack at McClure Pass hovered around the second-lowest measurement on record for a 30-year period.
By Thursday, March 22, the McClure Pass site and the Independence Pass site had dipped to the lowest ever recorded snow-water equivalent for that date.
“It’s a very notable statistic because [McClure Pass] has a pretty long period of record — 38 years,” said Karl Wetlaufer, a National Resources Conservation Service hydrologist and assistant supervisor with the Colorado Snow Survey. “It definitely indicates there will be well below normal streamflow resulting from those areas.”
It’s one thing to read about record low snowpack in a graph, and quite another when you see what it looks like on the ground where the data is gathered.
At an early March Water Education Colorado workshop, participants traipsed around McClure Pass on snowshoes digging snow pits, measuring snow depth, and testing the snow-water equivalent of snow samples, looking for clues about this year’s spring runoff.
That’s because today’s snow is tomorrow’s water.
At the top of the 8,755-foot pass is a SNOTEL (short for snow telemetry) site, which is an automated system of sensors that collect weather and climate data hourly and beam it to the NRCS office in Boise, Idaho. There are 115 SNOTEL sites across Colorado, mostly in remote, mountainous watersheds.
SNOTEL sites have a precipitation gauge, a pressure-sensing snow pillow, a snow-depth gauge, and an air temperature sensor. Some enhanced sites measure soil moisture content and humidity. They run on solar panels and also come equipped with a small shelter that housees the cables and wires that run the unit.
Currently, the snow-water equivalent at McClure Pass is around 55 percent of normal and the water year-to-date precipitation is around 62 percent. Manual measurements from the group recorded the McClure Pass snowpack at around two feet deep and the snow-water equivalent, which is the liquid content of the snow, measured around 21 percent.
The information gleaned from SNOTEL sites as well as from manual measurements by hydrologists can reveal a lot about what to expect from spring runoff.
The entire Roaring Fork watershed is at 76 percent for snow-water equivalent and 67 percent of normal for water year-to-date precipitation. The National Resources Conservation Service releases a monthly water supply outlook report based on SNOTEL data. For March 1, the Roaring Fork Basin was predicted to be at 59 percent of average volume for April through July. That dropped to 49 percent of average by mid month.
Not just depth
Snow-water equivalent is the best predictor of streamflow volume, but there are other factors that can affect the volume, and especially the timing, of spring runoff. Some of those include the date when the ground becomes free of snow cover, solar radiation, whether there is a layer of dust in the snowpack, and the soil moisture conditions prior to winter’s first hard freeze.
Liza Mitchell, education and outreach coordinator with the Roaring Fork Conservancy, explained that an earlier bare ground date means thirsty plants sprout earlier and absorb the water out of the soil, leaving less to flow into streams. Likewise, a dry fall means lower runoff. If dried-out soil froze with empty pore space, the snowmelt will fill these empty spaces in the soil first, instead of flowing into waterways.
Dust on snow and solar radiation also can affect streamflow volume and timing. Spring storms from the southwest can deposit a layer of dark-colored dust on top of the snowpack causing it to melt quicker. Sometimes the dust layer is buried several inches or feet down.
“If you have bright white snow, most of the solar radiation is going to get bounced off,” Mitchell said. “If there’s a dust event, it can change the reflectivity of the snow. Now that solar radiation is hitting a darker surface, most of the energy is being absorbed by the snowpack.”
NRCS streamflow forecasts are created using only the SNOTEL data and don’t take into account these other environmental variables. The reason for this is mostly for simplicity’s sake. NRCS manages about 600 streamflow forecasts throughout the western United States with a limited staff, said Angus Goodbody, a Portland, Oregon-based NRCS forecast hydrologist.
“If you have a good way to account for these other factors, then yes, they should improve your forecast,” Goodbody said. “But the biggest impact [these other factors] will have is not on the total volume, but the timing of runoff. We are predicting total volume, not when it’s going to happen.”
So who could potentially be affected by low stream flows this year? The city of Aspen, for starters.
Margaret Medellin, utilities portfolio manager for the city, said she will meet with City Council in April to discuss whether to implement water shortage restrictions in the coming months. The municipality does not have much water storage in the form of reservoirs, and it is required to keep a minimum amount of water in its stream sources of Maroon and Castle creeks.
In Stage 1 restrictions, the city would ask residents to voluntarily reduce their water usage by 10 percent in what is essentially an awareness campaign. Stage 2 would require some restrictions on outdoor water use and Stage 3 could ban it altogether. All three stages would see an accompanying increase in water rates.
“The city is committed to not drying up the creeks, so if they fall below a certain level, we stop diverting,” Medellin said. “We will use the little storage we do have or switch between one creek and the other.”
Some irrigators, especially those with lower priority water rights, could suffer as a result of low stream flows. But the biggest loser would probably be instream flows and ecosystems, said Andy Schultheiss, executive director of the Colorado Water Trust.
Instream flow rights are typically junior to most other water rights and streams can go dry in years when there isn’t much snowmelt coming down from the high country.
“People in their homes won’t notice much of a difference, but that doesn’t mean there aren’t some really bad things happening,” Schultheiss said. “In even moderately dry years, the fish and the whole ecosystem tends to congregate in smaller and smaller pools, which creates disease and competition for food.”
One potential solution is a pilot program that would let water rights owners lease water rights to the Colorado Water Conservation Board in order to keep more water in the stream. The Colorado Water Trust is a partner in this new voluntary water-sharing program that would benefit the state’s instream flow efforts.
For more information or to track SNOTEL data, go to https://www.nrcs.usda.gov/wps/portal/nrcs/main/national/water/snowsurvey/
From The Glenwood Springs Post Independent (Jon Nicolodi):
SnoTel sites are automated stations that collect data on snow, operated by the Natural Resources Conservation Service, and there are 115 in Colorado alone. While numerous measurements are taken, the most commonly used is snow water equivalent. Snow height is measured, but it doesn’t take into account the density of the snow, which can vary between 5 percent and 20 percent.
The snow water equivalent is measured in inches and can best be thought of as what the depth of the water would be if you instantaneously melted the entire snowpack. Snow height is a favorite measurement of skiers and snowboarders. Snow water equivalent is a favorite measurement of scientists and anyone looking at water beyond the winter, which is a popular notion in Colorado.
In an end-of-February report, Nick Barlow at the Colorado Avalanche Information Center reported the snow water equivalent of all of Colorado to be averaged at 73 percent, compared to what it historically is at the end of February.
But not all areas of Colorado are favored equally with snowfall. The Front Range, including the North and South Platte basins, are at 90 percent and 91 percent, respectively. The lower half of the state, including the Arkansas, Gunnison, Upper Rio Grande and the southwesternmost watersheds, are in the low 60s or high 50s, bringing down that state average. The Yampa and the White in northwestern Colorado are at 81 percent of snow water equivalent compared to a median year.
The Colorado River watershed, including the Roaring Fork and any other tributaries joining the Colorado along the I-70 corridor, comes in at 85 percent relative to its median snow water equivalent. On the whole, not too shabby. But not inspirational either.
In most of Colorado, higher-than-average snowfall in February greatly helped these percentages. All of the previous months had been a bit dismal for winter, with November and December being particularly dry. The storms that did come were flanked by warm weather, so large portions of our snowpack melted away. In an average year, that snowpack and its snow water equivalent reach peak numbers by April 9 before melting as a whole, contributing to all of the industries that rely upon a hearty spring thaw, ample soil moisture and flowing water as deep into our dry summers as possible.