Lake’s water warms up, as hot weather pairs with calm wind |

Lake’s water warms up, as hot weather pairs with calm wind

Melissa Siig

More people may be finding it easier to take a dip in Lake Tahoe this summer, as a combination of hot weather and lack of wind has made the lake unusually warm. However, the lake’s rising temperature is not unique to this summer. The water has steadily been getting warmer over the past few decades, scientists say.

On average, Lake Tahoe’s surface water can get as high as 68 degrees in the summer months. This year has already surpassed that number. In July, the lake’s temperature reached the mid-70s.

Brant Allen, Tahoe Research field laboratory director, attributes the lake’s warmer waters to this summer’s heat wave and lack of wind. While not breaking records, air temperatures have been close to record highs. The peak came on July 20 and 28, when temperatures soared to 93 degrees. That matches the highest recorded temperature for Lake Tahoe, set in 1934, according to Rudy Cruz of the National Weather Service in Reno. The average summer temperature for Tahoe is around 80 degrees.

“It is warmer than usual because we’ve had hot weather and calm weather until recently,” Allen said. “That temperature helps to warm up the lake.”

The lake’s surface temperature is always warmer than the water below 60 feet. When there is no wind to mix up the warm and cold water, the surface water remains warm. “When there is no wind we can get very warm waters on calm days,” Allen said.

Even though the area saw record snowfall this winter, Allen said that the snowmelt and run-off does not impact the lake’s temperature since cold water, which is denser than warm water, sinks to the bottom.

The lake’s rise also did not set any records, although it came close. According to Chad Blanchard, chief hydrologist with the Federal Watermaster’s Office in Reno, this year saw the second largest physical rise since 1995, but only because the lake started out so low. In terms of actual inflow to the lake, this year ranked sixth since 1900.

“It was a very good year, there was lots of run-off, but it was not the biggest,” Blanchard said.

The lake reached its peak on July 10, when the waters finally stopped rising.

Is it unusual that the lake is so warm this year despite the amount of inflow it received? No, says Tahoe Environmental Research Center Director Geoffrey Schladow, who said that the lake’s water temperature has been rising for the last 30 years.

While data for this year is not complete, Schladow said that last year the lake was warmer than the previous year. “And it seems warmer this summer,” he said.

The main reason for the increase in the lake’s temperature is that the nighttime minimum temperature is increasing. Over the last 100 years, the nighttime temperature has gone up by 3 to 4 degrees, Schladow said. On July 23, the nighttime temperature of 59 degrees broke the previous record of 57 degrees in 2003, according to the National Weather Service.

“As the nighttime air temperature gets warmer and warmer, the lake doesn’t cool off as much as it used to,” he said.

With the wind finally picking up last week, the air temperature cooled down to the low 70s. Nevertheless, thanks to global warming – which Schladow blames for the warmer night weather -we can expect Lake Tahoe’s waters to keep warming up for many years to come.

“It’s not going down any time soon,” he said.

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