New twists as Mono Lake’s level falls: Spotlight on lake level forecasting in 2016October 29th, 2015 by Geoff, Executive Director
California’s four-year drought has lowered Mono Lake more than five feet. The decline has been disappointing to watch yet ecologically survivable thanks to the protections won by the Mono Lake Committee and Mono Lake advocates two decades ago. 2016, however, could change this story for the worse.
The winter of 2015–16 lies ahead, and a wet winter with ample Mono Basin precipitation is the hope of all Mono Lake friends. But as we have learned over the years at the Committee, our work is most effective when we hope for the best and prepare for the worst. In this case, another dry winter that pushes the state into a fifth drought year would push new and potentially contentious Mono Lake management issues to the forefront.
The landbridge to the gulls
The fall in lake level to date has caused the landbridge near the lake’s north shore to re-emerge and grow ever bigger, threatening to provide a pathway for coyotes to predate the California Gull rookery on Negit Island and surrounding islets. A modest protective moat of water remained in place this past summer, but it won’t last through another dry year. This is a critical situation that raises many management concerns and even gained attention on the front page of the Los Angeles Times over the summer under the headline “An ominous level: Mono Lake crisis threatens wildlife, L.A.’s water supply.”
How might the nation’s second-largest California Gull nesting ground be protected? Committee staff have been talking with biologists, land managers, and Mono Lake friends who witnessed the landbridge during its previous appearance in the 1970s. There are many ideas, and the task for the winter is to determine which is the best to deploy—if needed. Assuming the full landbridge persists for a year or two until the lake rises, the most commonly discussed concept is a low-impact electric fence to create a temporary artificial barrier to coyote passage. Such a project would require state approval, possibly federal agency concurrence, funding, volunteers, and quick action.
Zero water export to Los Angeles?
Symbolizing how the protection of Mono Lake and the water supply of Los Angeles are intertwined, the water diversions the Los Angeles Department of Water & Power (DWP) is authorized to make each year are set based on the level of the lake on April 1. This year the drought-induced fall in lake level triggered a substantial cutback in water exports to Los Angeles. Next year the rules could be trickier to determine.
The lake level is currently 6378 feet above sea level. The water export rules recognize the ecological jeopardy the lake is in when it approaches 6377, and they add a twist. As usual, we measure the lake level on April 1—if it is below 6377, no exports are allowed for the following 12 months. That part is easy.
The twist is where hydrologic modeling takes center stage. The State Water Board rules also halt water exports if “Mono Lake is projected to fall below 6377 feet at any time during the runoff year of April 1 through March 31.” Making such a projection is routine—DWP and the Committee do it every year—but results can differ depending on the assumptions that are required to predict a year’s worth of precipitation and snowmelt runoff.
The big questions for next year are: Is DWP willing to work collaboratively to deliver a consensus science-based projection? How do we resolve differing lake level projections, most notably if DWP’s stays above 6377 feet and the Committee’s does not? This is new ground because these particular State Water Board rules haven’t yet been needed in the 21 years since they were issued. Being prepared is critical, and the time to do it is well before springtime. In fact, the Committee is already exploring ways to access more precise Mono Basin snowpack data to ensure the most honest snowmelt runoff and lake level forecasts possible.
And the magic runoff number is….
Most Californians are ready to embrace as wet a winter as nature will give us. So are those of us in the Mono Basin. But to be more specific, the Committee’s hydrologic modeling analysis shows that to keep the lake above the critical 6377-foot elevation, next year’s runoff needs to be at least average. That’s certainly in the range of possibility, with the odds being near 50/50 based on recent decades, and probably better given strong El Niño conditions already being observed. All we can do now is wait—and plan for contingencies. As we prepare to help Mono Lake through another potentially dry year you can be sure that we will be counting every snowflake here in Lee Vining in hopes of a wet winter.
This post was also published as an article in the Fall 2015 Mono Lake Newsletter (pages 3 & 4).