Oroville Overview

An aerial view of Lake Oroville and the Oroville Dam complex in 2019.

Dry conditions during the state's 2020 water year translated into a dramatic cut in hydroelectric generation sent to the California ISO grid, according to recent reports.

The snowpack—the 10th smallest since 1950—cut available hydro output by 45 percent.

The California Department of Water Resources report highlights were issued Oct. 1, while CAISO's Department of Market Monitoring (DMM) released its second-quarter report Oct. 6.

In the summary of conditions in the 2020 water year, which spans Oct. 1, 2019, to Sept. 30, DWR said the snowpack was 50 percent of average on April 1.

"Much warmer than average statewide temperatures occurred during the key winter snowpack accumulation months, continuing a long-term trend of warmer statewide temperatures that began in the 1980s," the report summary says. "The April 1st statewide estimate of snowpack water equivalent, representing the time of typical maximum snowpack accumulation, was 53 percent of average based on electronic sensors or 50 percent of average based on manual snow course measurements."

Storms late in the season increased the peak snowpack to 66 percent of average. That measurement was also made through the sensor network.

Both the DWR eight-station precipitation index—which tracks Sacramento River basin conditions—and the five-station San Joaquin precipitation index ended at 62 percent of average. The Tulare Basin index ended at 65 percent of average.

Although the water year started with "promising" amounts of precipitation in November, January and February were dry. Those dry conditions persisted in Northern California, while Southern California—San Diego County and the Inland Empire in particular—had above-average precipitation from storms late in the year. San Diego had "one of its wettest Aprils on record," according to the report. In contrast, the Russian River watershed experienced its third-driest year on record.

DWR also found state reservoirs had only a third of the water runoff from precipitation and snowmelt compared with the year prior. "The impacts of dry conditions were tempered, however, because of good reservoir storage from a wet 2019. Statewide reservoir storage through the end of September 2020 is projected to be 93 percent of average or 21.5 million acre-feet."

Meanwhile, the CAISO DMM found that although generation from renewable resources in the second quarter increased by roughly 60 percent compared with the first quarter, year-over-year total renewable generation dropped 15 percent, which CAISO attributes "primarily" to a 45-percent reduction in hydroelectric production.

In its analysis, the DMM report states that renewable generation from hydro, solar and wind usually peaks in the second quarter. It referred to the DWR report and compared the 50-percent 2020 snowpack to the 175-percent-of-normal snowpack measured on April 1, 2019.

Compared with the previous quarter, hydroelectric generation increased about 67 percent, according to the DMM. It added that hydro generation "declined in all hours of the day compared to the same time last year." And, as was the case in the first quarter, imports "consistently" produced more than hydro resources throughout the day.

The DWR report also said wildfires pose significant danger to hydropower infrastructure. Wildfires threatened DWR's Lake Oroville facilities and Southern California Edison's Big Creek System, as well as small rural water systems.

"California is experiencing the impacts of climate change with devastating wildfires, record temperatures, variability in precipitation, and a smaller snowpack," DWR Director Karla Nemeth said in a news release. "We must continue to invest in our infrastructure to prepare the state to cope with more extreme weather for the state's needs today and in the future."

The DWR report says the great amount of year-to-year variability in precipitation means any year can potentially have either record-wet or record-dry conditions.

"In the absence of the ability to reliably predict seasonal precipitation, Californians must be prepared for the possibility of extreme wet or dry conditions in any water year," the report says