Heat waves

Scientists and land managers at Lake Tahoe are partnering in an effort to consider one of the most important questions faced there—how Tahoe might cope with a steadily warming climate in the years and decades to come.

The ultimate goal is to enhance the Lake Tahoe Basin’s ability to adapt to climate change and, in doing so, protect it from changing climactic conditions.

“It’s obvious that it’s happening. The evidence is right in front of us, and it’s something that we can all observe,” said Whitney Brennan, the project lead for the California Tahoe Conservancy, which is heading up the effort. Indeed, scientists have for years documented a steady increase in both air and water temperatures of the Lake Tahoe Basin.

Water temperature measurements taken in 1970 showed the lake’s year-round temperature averaged about 50 degrees. This reached more than 53 degrees by 2015, say scientists at the UC Davis’ Lake Tahoe Environmental Research Center. The change, most of which occurred during the previous decade or so, was believed to be associated with rising air temperatures.

Evidence of warming was particularly startling in 2017, when Lake Tahoe’s average surface water temperature hit 68.4 degrees, 6.1 degrees warmer than July 2016 and the warmest ever measured at the lake.

At one point in August of last year, shallow water temperatures at Sand Harbor were recorded at 74.5 degrees, only about 4 degrees less than what was recorded in shallow ocean water near San Diego.

New climate models prepared at Davis predict Tahoe air temperatures could rise by seven to nine degrees between now and the end of the century, a trend that would translate to corresponding increases in water temperature.

Changes could come with many worrisome impacts to Lake Tahoe, among them less “mixing” of the lake’s warm surface water and colder waters near the bottom. That could change the lake’s chemistry and promote blooms of algae growth, robbing the lake’s famed clarity.

“At some point, the lake may stop mixing all the way to the bottom,” said Geoffrey Schladow, director of the Environmental Research Center. “The warming of the lake, especially the warming of the surface, I suspect, is going to profoundly change Tahoe.”

Warming could mean the loss of native species such as minnows and the spread of non-native, invasive species. Already ailing forests could become increasingly susceptible to drought, insect attack and wildfire. More rain could fall instead of snow, leading to flooding and increased erosion. Skiing and boating could be affected, undercutting Tahoe’s tourism-dependent economy.

Participants are now in early stages of assessing Tahoe’s vulnerabilities to climate change. Future steps will focus on improving the basin’s ability to adapt to changes. Potential actions could be identified to build preparedness and reduce greenhouse gas emissions linked to climate change.

“To me we’re developing this because we want to make sure that we are, as a whole, addressing all climate change impacts and resources that are at risk,” Brennan said. “We really want to make sure we’re really looking at the basin comprehensively, and there are no gaps.”

There’s really little time to lose, Brennan said.

“It’s already happening, and it’s going to increase,” she said. “I think it’s a real threat.”