State of the Lake:Both air and water temperatures in Lake Tahoe Basin on the rise

In June, 2018, we found out the epic clarity of Lake Tahoe was measured at an average of 59.7 feet in 2017, a 9.5 foot drop from the previous year and 10.3 feet lower than the five-year average according to a report compiled by the Tahoe Environmental Research Center (TERC) at the University of California, Davis.

This measurement surpassed the previous lowest level of 64.1 feet which was recorded in 1997, but far below the record high of over 100 feet in the mid-1960s.

This week, TERC released their annual State of the Lake Report, a report card of of Lake Tahoe. In their report, TERC summarized the following key points: Clarity in 2018 appears back on track, but learning from lessons of 2017; 2017 had record-breaking air and lake temperatures. Was one of wettest years, too; and Tahoe in 2100 could be 9 degrees hotter

Both the average air and the water temperatures in the Lake Tahoe Basin are the warmest on record, even with a winter where the monthly air temperatures were cooler than recent years. The average temperatures were warmer during summer, resulting in 11 of the 12 months having air temperatures higher than the 1910-2017 average.

Lake temperature was the warmest on record. Surface water temperatures in July 2017 were the warmest ever recorded at 68.4 degrees, which was 6.1 degrees more than in 2016.

Water Year 2017 (Oct. 1, 2016-Sept. 20, 2017) was the second wettest on record, with 68.9 inches compared to the long-term average of 31.6 inches.

“While 2017 may be viewed as an anomalous year, it has reinforced the fact that progress toward environmental restoration of Lake Tahoe will be punctuated by extreme years in future decades,” said Geoffrey Schladow, director of the UC Davis Tahoe Environmental Research Center, or TERC. “Monitoring these extreme years and applying the lessons learned will be critical to ensuring that the lake and its watershed have the resilience needed to thrive under future conditions.”

The drop in clarity was likely due to the one-two punch of the end of a five-year drought followed by a winter of record-high precipitation levels that extended well into the spring. More sediment washed into the lake in 2017 than the previous five years combined, according to the report.

Clarity readings from the first half of 2018 indicate that clarity is back in its normal range, suggesting 2017 was an outlier. Nonetheless, the report said the decline highlighted the reality that extreme climatic and hydrologic events will become more common in the future and that current monitoring efforts need to be reviewed and upgraded to prepare for them.

TERC climate change researchers are applying downscaled future climate projections to the Tahoe Basin. The results suggest air temperatures will rise by 7 to 9 degrees Fahrenheit between now and the end of the century. The watershed will also dry considerably, particularly on the north and east sides, adding to forest stress and wildfire risk.

To read the complete report, visit http://tahoe.ucdavis.edu/stateofthelake/index.html.