Lake Mendocino reaches second-lowest level in history

Historic drought has reduced Lake Mendocino to its second-lowest level since it was built, leaving reservoir storage in startling condition with months of likely warm, dry weather still ahead.

The lake on Thursday held just more than 24,000 acre feet of water — a result of critically low rainfall totals that, combined, make 2019-21 the driest two years on record, the National Weather Service said.

Storage in the reservoir, completed in 1958 with a flood storage capacity of 122,400 acre feet, has dipped below 25,000 acre feet only three times before and below 24,000 acre feet only once — by half, according to Sonoma Water.

In Nov. 1977, it registered a terrifying record low of 12,081 acre feet in the days before the rainfall returned after two punishing years of drought that brought a combined 35.6 inches of rain to Ukiah, according to the National Weather Service. Ukiah is just a few miles from Lake Mendocino and the best measure of inflow available to the reservoir.

So far this year, Ukiah has received 13.48 inches of rain, for a total 28.23 inches between this year and last. The rainfall year runs from Oct. 1 to Sept. 30 for weather service record keeping purposes.

The improved storage level in Lake Mendocino now compared with 1977 is due to modern, forecast-informed reservoir operations that allow water managers to deviate from stringent, wintertime flood control protocols when there is no sign of storm activity in the forecast.

This year, the new guidance allowed managers to hold back 11,000 acre feet of water behind Coyote Dam that otherwise would have been released to make room for stormwater that never came.

An acre foot is almost 326,000 gallons of water, or enough to flood most of a football field one-foot deep. Though water usage varies from community to community, in part based on climate and housing density, an acre foot is about what’s needed to supply almost 3½ water-efficient California households for a year, according to the Water Education Foundation.

State and local water managers have been reducing withdrawals from the Russian River to slow releases from Lake Mendocino in hopes of ensuring the level does not drop below 20,000 acre feet before Oct. 1, in case another dry winter lies ahead.

You can reach Staff Writer Mary Callahan at 707-521-5249 or mary.callahan@pressdemocrat.com. On Twitter @MaryCallahanB.