Robust streamflow projected in NV this summer
As the snowpack accumulates, hydrologists can estimate the runoff that will occur when the snow melts. (USDA Natural Resources Conservation Service video screenshot)
Nevada can expect robust streamflow well into the summer and brimming reservoirs into the fall as federal water managers forecast snowmelt twice that of previous years.
After four months of above average snow and rain, March saw the biggest snow accumulation on record across the Sierra Nevada and Great Basin, with some records dating back 80 to over 100 years.
March was the fifth consecutive month with above normal precipitation across the state, according to the latest data from the U.S Department of Agriculture. Major sources of water for Nevada — including the Eastern Sierra Nevada mountains, the Upper Colorado Basin, and Spring Mountains — accumulated snowpacks far above typical ranges in April.
Most of the annual stream flow in the western United States originates as snowfall that accumulates in the mountains during the winter. As the snowpack accumulates, hydrologists can estimate the runoff that will occur when the snow melts. This time of year is especially important for water supply forecasting in the West, as it marks the peak of the snow accumulation season and planning for the spring and summer water can begin in earnest.
Snow water measurements across the Carson and Walker basin have surpassed all previous peak snow water amounts for any year back to 1981. The Lake Tahoe, Truckee and Upper Colorado basins are also approaching all-time peak snow water amounts based on daily SNOTEL data from Natural Resources Conservation Service monitoring stations.
As a result, reservoirs with more storage space are still gaining, while smaller reservoirs are being drawn down to create space for expected snowmelt in the coming months. In the Tahoe and Truckee basins Stampede, Prosser, and Boca reservoirs are all expected to fill. In the Carson Basin, there is more than enough water to fill Lahontan.
In the Humboldt Basin, water is again flowing the length of the river to Rye Patch Reservoir. But federal water managers warn that predicting streamflow for the Humboldt River will be extremely challenging this year due to prior dry years.
Conditions have also improved west of Las Vegas, where long-term precipitation deficits lessened and groundwater and soil moisture locally improved.
Record snow packs, however, could not overcome decades of drought conditions this winter.
For the Colorado River system, the U.S. Bureau of Reclamation reported that as of April Lake Mead is at 28% capacity while Lake Powell is at 23% capacity. While the snow pack suggests better flow levels into both reservoirs than in some of the prior years of the drought, it is still too early to project what the impact will be on reservoir levels, BuRec said.
While the U.S. Drought Monitor indicates about 22% of the state is now out of drought conditions, another 24% of Nevada is still experiencing severe to exceptional drought.
Forecasters said expected streamflows will not be enough to fill Lake Tahoe. Still, Lake Tahoe has benefited somewhat. Last fall, Lake Tahoe was half a foot below its rim but has nearly recovered, according to the Natural Resources Conservation Service. Reservoir storage in the Lake Tahoe Basin has also recovered to about 40% of capacity, compared to 18% last year.
Experts warn that snowpacks have become unpredictable and inconsistent, meaning one wet year will likely be followed by several dry years.
“This is one of the coldest winters we’ve had in decades, but that is not expected to continue year after year. This is definitely an anomaly. We’ve had warmer winters over the last few decades and that is likely to continue,” said Dan McEvoy, a regional climatologist with the Desert Research Institute, during a panel discussion organized by the Nevada Wildlife Federation last week.
Potential for floods and wildfires
With all-time record snowpacks in the Carson and Walker basins, the potential for flooding this spring is likely, say federal water managers. The wide ranging snow coverage means that snow melt could occur across a much larger area resulting in flash-flooding if there is a sudden warm-up.
Throughout this week, the West will see a significant warming trend that is expected to increase streamflow due to melting snow, heightening flood concerns. Early in the week, temperatures are predicted to briefly top 95°F in lower elevations of the Desert Southwest, according to Brad Rippey, a meteorologist with the USDA.
Major flooding and drought are likely the new normal in Nevada, say experts.
“We’re used to a year-to-year swing from wet to dry, but what we’ve seen is that variability is getting larger.” said McEvoy. “There are a lot less years that are normal and more that are outliers and in the extreme. I think we’re going to continue to see those flips from extreme wet to extreme dry.”
Wildflowers are blooming across Death Valley and southern Nevada, a welcomed outcome. However, in the lower hills of western Nevada rain and snow has also led to a large growth of cheatgrass, a highly flammable invasive grass.
“This whole winter as we’ve had all this snow there’s been little cheatgrass seedlings growing big and strong under that snowpack and we’re expecting that to kick our butts,” said August Isernhagen, the division chief of Wildland Fuels for the Truckee Meadows Fire and Rescue.
Cheatgrass grows fast and dries out quickly, priming wildfire season for an earlier and more intense start.
“We are primed to burn a month or two sooner in the year. It’s one of our biggest fire problems,” Isernhagen said.
Wet years typically result in a bigger annual grass crop, but with cheatgrass choking out native vegetation and fueling wildfires, the state is seeing larger fires in the lowlands across the state, Isernhagen said.
In the past, the landscape could recover fairly quickly from grassland fires compared to tree fueled fires. But continuous fires have razed the state’s grasslands.
“In the lowlands, we would expect fire to come in, wipe out it out, and within 10 years you’ve got a nice sagebrush ecosystem but know because of cheatgrass it burns year, after year, after year and it never returns back to that sagegrass ecosystem,” Isernhagen said.
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