As of May 9, most reservoirs in California are over or near their historical average capacity. But there’s a glaring exception: Trinity Lake. According to the Department of Water Resources, Trinity Lake is only at 49% of its historical average capacity and 39% of capacity overall.
If you look at other prominent lakes around Northern California, including Shasta and Oroville, the water levels are at their highest levels in years. So why is Trinity Lake filling at a slower rate than other reservoirs?
First and foremost, the region surrounding Trinity Lake received less rainfall than other regions of NorCal, although it was still much higher than average this winter in terms of precipitation. On top of that, Trinity Lake relies heavily on snowpack for water, which is much different than nearby reservoirs. Shasta, on the other hand, is much more dependent of rain than snow.
Much of the snowfall may not melt and flow into the reservoir until late spring or summer. That means that despite high levels throughout the region right now, Trinity won’t fill up until later this summer when temperatures rise and snowmelt enters the basin.
The atmospheric rivers that hit California since December have primarily focused on the Bay Area and Central Coast, with some reaching the Los Angeles region. Only a few were directed at the Klamath Basin, where Trinity Lake is located. This year, most atmospheric rivers have shifted a couple of hundred miles south, leaving the far north less wet than usual.
While some areas of California may no longer be classified as being in a drought, they will still face long-term water supply problems. The Drought Monitor may not accurately reflect California’s situation, as it doesn’t account for groundwater conditions and the state’s water transportation. As Jay Lund, Vice Director of the UC Davis Center for Watershed Sciences, points out, “water scarcity is enduring.” Groundwater recovery in the San Joaquin and Sacramento valleys may take years, and the Klamath Basin still faces ongoing water use conflicts between agriculture and ecosystem preservation.
As it stands, a single wet year won’t be enough to compensate for the cumulative loss of precipitation experienced since 1997. It will take more than one wet year to truly break free from the drought’s grasp and its impact on ecosystems and water systems.
For Trinity Lake, that means lower water levels for the time being.