Drought impacts: Tahoe likely to drop below rim in 3 months
Special to the Sierra Sun
After two consecutive dry winters, Tahoe’s lake level is sitting a little over 1.5 feet above its natural rim — a threshold the alpine lake is forecasted to drop below in the next three months.
And while the rise and fall of Lake Tahoe’s water level is cyclical in the short-term (with evaporation and downstream flow offsetting spring runoff filling the lake each year) and the long-term (the lake has fallen below it’s natural rim over 20 times in the last century since data collection began), experts are concerned by the severity of the current drought and its impacts on water supply, wildfires and wildlife.
To start, it’s the third driest year in terms of precipitation from melted snow and rain in 111 years, reports Chad Blanchard, the Federal Water Master responsible for upholding the legal mandates of Tahoe’s water flow.
According to the 11 Snow Telemetry (SNOTEL) weather stations in the basin, cumulative precipitation currently sits at 23.6 inches — 53% of average and just shy of the 22.6 inch record-low for this time of year.
Evaporation — which accounts for the loss of 55% of the six feet of reservoir water stored between the lake’s natural rim and the Tahoe City dam — continues to outpace inflow, which was low this spring due to below-average snowpack and ground absorption from dry soil conditions.
To a much lesser degree, water is lost from the lake due to release from the dam to meet downstream water demands.
“Floristan rates are the required rates of flow we have to meet year round. Those are the flows that meet power generation, municipal, industrial, and agricultural demands. That’s the way it’s been since 1908,” explains Blanchard. “If natural flow does not meet those rates and we have water in storage, we have to release that water legally to meet those rates.”
The release this spring of additional water credits banked from previous years for downstream recipients also accounted for a marked drop in the lake’s level.
A recent forecast predicts that in three months, the lake will drop a foot and a half, bringing it below its natural rim, says Blanchard. All but three inches of the drop from release downstream will be from evaporation. Though rainfall or higher evaporation rates could impact this timeline, falling below the rim could cause issues for downstream demands.
“There will be some impacts to downstream users this year, but they will be fairly limited because of carry-over storage that we had, however, going forward will entirely depend on what happens next year since our carry-over storage has been significantly reduced or depleted,” says Blanchard. “We could have a big winter and hit the reset button and be done with drought talk until the next cycle or we could be in deeper.”
There are a number of consequences the current drought conditions and low water can have on the ecological balance of the basin and beyond.
“The low water conditions are probably affecting the growth of something called metaphyton, a sinuous, free-floating weedy kind of algae that occurs in strands particularly when we have warm water conditions as we do now, and when lake water levels are low it tends to get washed up on the beaches particularly on the South Shore,” notes Geoff Schladow, director of the U.C. Davis Tahoe Environmental Research Center. “We think it’s going to be happening more and more this coming summer. You are going to see that and smell that. There will be more bugs in the air because of it, and suddenly Tahoe’s beaches are not these wonderful things that we like them to be.”
Without inflow from Tahoe into the Truckee River diluting nutrients and contaminants, Pyramid Lake, located downstream and northeast of Reno, will likely experience higher concentration of urban runoff and discharge from wastewater treatment plants in Reno and Sparks, adds Schladow.
Additionally, streams flowing into Tahoe that serve as spawning grounds for the kokanee salmon, including Taylor Creek, may trickle out upstream of Tahoe, forcing the fish to lay their eggs in the less-than-ideal shallow waters near beaches.
Though drought conditions often limit food and water sources for bears, forcing them into unusual places like neighborhoods, the bear activity on the Nevada side of the lake has been average this year. Between June and mid-July, the Nevada Department of Wildlife received 66 bear-related calls, ranging from sightings to reports of the creatures on properties. By comparison, a natural food shortage last year led to a spike in bear-related calls totalling 171 in just June and July.
“If this prolonged drought continues, this could change, and it could lead to more wildlife interactions in neighborhoods as wildlife searches for food and water,” cautions Ashley Sanchez, NDOW public information officer.
The hot, dry conditions in the basin have, not surprisingly, put the Tahoe Basin at a high-risk for wildfires, though so far there have been no major blazes.
“One of the things specifically around the basin that we’ve noticed is that the fuel moisture — the amount of moisture in the plants and trees — is very, very dry compared to the normal conditions this time of year,” explains Brian Newman, division chief for the Cal Fire Amador-El Dorado Unit. “We’re roughly four-to-five weeks ahead in regards to our drying cycle as we would be in a normal year.”
Though fuels reduction work continues throughout the basin, Newman notes that a vast majority of fires in the basin continue to be human-caused, whether started by a cigarette tossed on the ground or a spark from a trailer chain dragging on the road.
“Fortunately, we haven’t had anything major as far as fires in the basin so far, but we’ve had quite a bit of ignitions, and even the small fires we’ve had have burned pretty hotly and more than they should this time of year. We’re definitely noticing that difference,” says Newman.
Fire officials urge visitors and locals alike to visit http://www.tahoelivingwithfire.com to stay up-to-date on the current fire danger and red flag warning.
Rising temperatures in the 90s over the past week have Tahoe residents concerned about more than just their lack of air conditioning.
“We obviously have a huge amount of climate variability in our region, but it is very disconcerting because what we know about our observed climate and our modeled future climate is that these kinds of temperatures are going to be more normal going forward,” says Tim Bardsley, hydrologist at the National Weather Service in Reno. “The precipitation we don’t know as much about — how that’s going to change or not — but we are confident about the temperature change. That alone exacerbates drought. It increases our evaporation. It increases our water demands.”
Unfortunately, notes Bardsley, there isn’t a great mechanism to accurately predict long-range precipitation and how this drought might play out.
“A lot of this is probably tied in with climate change,” agrees Schladow. “Just looking at the data that is collected every 15 minutes on the lake level, we can see going back a 100 years that we’re starting to get these highs and lows more frequently. In the past, it didn’t change that much. Now it goes from a high to a low in literally two years.”
A big concern, says Schladow, is for lakes and reservoirs across California that are more susceptible to water loss, like Shasta Lake, which is facing its lowest level in at least 44 years.
While Tahoe can be filled to the brim after one good winter — like the drought-busting 2017 season which filled the lake to the brim and spilled more down the Truckee — most lakes aren’t so lucky.
“If we have another dry winter, we’ll get some increase in water, but not what Tahoe needs to stop it from going below the natural rim again next year. The bigger problems are for lakes elsewhere in California that are more prone to water level loss than Tahoe,” notes Schladow. “If there is a dry winter, then there really is an incredible water crisis looming.”
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