As California’s drought deepens, it is worth checking in on the status of water supplies and what might be in store for the rest of the summer, and beyond.
What started with the promise of a wet water year, ended up dry, again. In January, the 8-Station Index showed precipitation totals keeping pace with the wettest year on record. Then it got dry and accumulated totals flat-lined. The final result is a below average water year, although not one of the driest years on record. To be precise, we are 13.3 cumulative inches below the long-term average for the northern Sierras.
Current conditions in reservoirs are a mixed bag. Shasta Reservoir remains low at only 40% of capacity, and 49% of the historical average. On this same date in 2021, Shasta was 41% of capacity and 51% of long-term average. Thus conditions in Shasta are very similar to those observed last year. So holding coldwater to support eggs and juvenile winter-run Chinook salmon in the Sacramento River will again be a major challenge this summer. On the heels of a mostly failed year class of winter-run Chinook salmon in 2021, the run is now at perilous risk of extinction. After all, these salmon operate on just a three year life-cycle. Perhaps because of this, efforts have accelerated to move adult winter-run Chinook salmon into and . Juvenile outmigrants would have to be trapped and moved around structures on their way out (‘two-way trap and haul’), or fishways re-operated for the specific benefit of salmon (‘one-way trap and haul’). Neither management approaches have been attempted at scale before in these systems. Two-way trap and haul is notoriously expensive and managers have reluctantly avoided it in the past ().
Other reservoirs are faring better than one might expect. Oroville is at 53% of capacity and 67% of the historical average. For comparison, at this same point in 2021, Oroville was at 36% capacity and 46% of the historical average. Folsom Reservoir stands at a whopping 88% capacity and 111% of the long-term average – quite good for this point in the drought. This also compares favorably to only 34% of capacity and 43% of the long-term average for Folsom at the same date in 2021.
One potentially interesting observation is that many locally-operated reservoirs appear to be doing particularly well. New Bullard’s Bar and Don Pedro sport 102% and 82% of long-term average, respectively. These reservoirs were also decently full during 2021. Yet, the architecture of these reservoirs may partially explain this dynamic. For example, New Bullard’s Bar is a large capacity reservoir (969,600 acre-foot) but drains a watershed that is comparatively small; the entire Yuba River watershed is 857,600 acres. Similarly, Don Pedro has a capacity of 2,030,000 acre-foot and the entire Tuolumne River drains a watershed of 1,253,120 acres. In this sense, reservoirs with a high capacity:watershed ratio reservoirs may be more slowly impacted, and thus more durable over longer drought. ranked all major dams in California based on their degree of regulation (DOR). Both of these reservoirs had DOR values well >1, which was a threshold identified in the study for strong hydrologic regulation.
It is likely that high air and water temperatures will occur again this summer, as temperatures have been high for recent years. This will have specific and diffuse socioecological impacts. During the last drought, increased temperatures led to parched soils and stressed trees, and ultimately major forest mortality events (). Obviously, drought also increases frequency and severity of wildfires. . Last summer, the Dixie Fire was the largest of the 2021 wildfires, burning close to 1M acres in Butte, Plumas, Shasta, Tehama, and Lassen Counties. As of writing, there are already seven . How many major wildfires will accumulate during 2022?
Groundwater is taking a major hit. Water right curtailment orders will occur again this growing season. Growers that have planted annual crops will likely rely on groundwater in an attempt to finish. Tree growers with young crops may be forced to use groundwater or purchase water at high prices to try to keep trees alive. California produces ~80% of the world’s almonds and . Declining groundwater stores will . Land subsidence from reduced groundwater will impact the . Finally, overdraft of groundwater supplies from this year (and previous years, such as 2021) will make , and require repayment of aquifers for additional drought pumping in future years for many basins.
The Delta ecosystem continues its sad decline. The delta smelt is , and although , the habitat issues that historically plagued smelt remain . To a large extent they have gotten worse. Water temperatures continue to increase, and increased temperatures are a major factor in recruitment failures of smelt (). Longfin smelt are declining behind delta smelt (). Warmer temperatures and clearer waters (due to effects of non-native clams) have intensified the rate of spread of invasive aquatic plants. The switch of fish habitats from cold turbid waters to warm, clear and plant filled habitats has shifted the ecological regime in the Delta to . These species in turn, compete and predate on native fishes, which cause further declines in Sacramento Valley and Delta endemics.
Other drought-related impacts are emergent. Water prices are increasing across the board. San Diego County Water Authority will be charging for untreated water in 2023. Many growers that have elected to sell water rather than grow have received record sale prices. These effects are being further compounded by macroeconomic inflation. Urban water restrictions have already been put in place in much of the state. The economic fallout of agricultural water shortages will result in rising unemployment and . Amidst drought conditions, an interesting plan emerged earlier this month that involved the . The details and fate of this plan remain murky. As water becomes more expensive and scarce, there may be less interest and prioritization of environmental programs, even though drought is the time when these programs might be most needed by wildlife.
is a professor of Wildlife, Fish & Conservation Biology and Co-Director of the Center for Watershed Sciences at the University of California, Davis.