California's current record-breaking heat wave in July has caused hundreds of millions of gallons of water in Lake Shasta and other major reservoirs in Northern California to disappear into thin air.
During the first nine days of July, 3,392 cubic feet per second of water — or about 2.2 billion gallons — turned into vapor and floated away into the atmosphere off the man-made Lake Shasta. During just one day — July 3 — 288.8 million gallons of water alone evaporated.
That is a substantial amount of water, said Don Bader, area manager for the U.S. Bureau of Reclamation, which manages Shasta Dam. For comparison, he said that is more than the amount of water flowing down Clear Creek south of Redding.
"It affects where our projected reservoir levels will be at the end of the season," he said.
How has the California heat wave affected reservoirs?
Higher evaporation levels are expected during the summer, Bader said. This year, though, with temperatures breaking all-time-high records in Northern California, the evaporation has risen, Bader said.
"We haven't seen weather like that in a long time," Bader said.
The National Weather Service recorded a high temperature of 119 degrees at the nearby Redding Regional Airport on Saturday, July 6. According to the weather service, this was the first time Redding had ever endured a temperature over 118 degrees.
Lake Shasta isn't the only North State reservoir being robbed of water by the heat. During the first nine days of July, 828.5 million gallons of water evaporated off Trinity Lake near Weaverville, and Keswick Lake near Redding lost 47.1 million gallons to evaporation, according to the bureau.
Evaporation is not an issue in the winter and spring, when lakes are filling with snow melt and rain, Bader said. "In the wintertime we get the really cold days. You don't get any evaporation because the ambient temperature is so cold and the water's cold," he said.
The bureau does not measure the water evaporation from the Sacramento River, which flows some 380 miles from its source near Mount Shasta to the Bay Area.
Where does the water stored in Shasta Lake go?
Shasta Lake's primary function is storing water for irrigation for farmers in the Sacramento and San Joaquin Valley. That water is shipped up to 450 miles to the San Joaquin Valley for the 250 members of the Central Valley Project.
Shasta Dam, which results in Shasta Lake, also generates vast amounts of electricity, helps protect against floods downriver in wet years, and prevents saltwater intrusion into the Delta in dry years.
Shasta Dam was constructed between 1935 and 1945 across the Sacramento River. Shasta Lake was formed in 1948. The reservoir submerged the Pit and McCloud rivers and several smaller tributaries.
It is the largest man-made reservoir in California, with 365 miles of shoreline. The lake offers multiple recreation options, including renting houseboats, jet skis, inner tubes, and fishing boats.
How is water evaporation measured in California's reservoirs?
The bureau measures evaporation by placing water in a cylinder and measuring the amount of water lost over a 24-hour period, Bader said. The amount of evaporation in the cylinder is extrapolated to water in the lake, he said.
Could water evaporation in California's reservoirs be slowed during the summer?
The issue of freshwater evaporation has been studied for many years. In 2015, the University of Colorado published a report noting water loss in reservoirs throughout the West was a growing concern as droughts became more intense and frequent.
While covering reservoirs such as Lake Shasta might not seem feasible, some have considered such proposals.
"Proposed 'geo-engineering' techniques for reducing reservoir evaporation include covering surface water with thin films of organic compounds, reflective plastics or extremely lightweight shades. Other proposals include moving reservoir water underground into new storage areas or aquifers or relocating or building new storage reservoirs at higher elevations where less evaporation occurs," the University of Colorado report says.
During the 2015 drought, the city of Los Angeles experimented with reducing evaporation by covering reservoirs with plastic balls to reduce the heat over the water. However, having ping-pong balls in the water did not become a long-term solution.
Covering Lake Shasta with any material could be difficult, considering the size of the reservoir, which is the largest man-made lake in California, Bader said.
Reporter Damon Arthur welcomes story tips at 530-338-8834, by email at damon.arthur@redding.com and on Twitter at @damonarthur_RS.
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