Written by Robert Shibatani
After a record-setting December 2021, this past month has seen the exact opposite; demonstrating once again, the extreme nature (sometimes termed a “weather whiplash”) in California’s hydroclimatology. In many areas of the State, virtually no new precipitation was recorded while, in others, nominal accumulations were observed.
Year-to-date precipitation accumulations, however, remain above 100% of average for several locations, some of them, substantially (e.g., Blue Canyon in the upper American River basin), while elsewhere, accumulations have dipped below average (e.g., Trinity River basin and the San Joaquin River at Huntington Lake).
The Northern Sierra Precipitation – 8 – Station Index stands at 31.5 inches as of February 1st. This is above the approximate average of 27 inches for this date. For the San Joaquin Precipitation – 5 – Station Index, the current 20.2 inches is about average for this date. However, for the Tulare Basin Precipitation – 6 – Station Index, the current 13.0 inches is slightly below the 14-inch average for this date.
Statewide, across 100 snow measurement stations, averaged SWE stands at 15.9 inches which is about 92% of normal for this date. Across the northern, central, and southern regions, SWE values range between about 56-58% of the April 1st average and between 90-95% of normal for this date.
CVP reservoir storage stands at 4.502 million acre-feet (MAF) which is about 37.8% of the CVP reservoir’s full system capacity or 67.6% of the 15-year average. Oroville Reservoir is storing about 1.642 MAF, which represents about 46.4% of the reservoir’s capacity (and 94% of its 15-year average for this date).
The contrasting operations of the CVP’s large and small reservoirs was quite telling during this month. Folsom Reservoir for example, with a capacity of only 977 thousand acre-feet (TAF), was maintaining an “empty space” conservation pool at or above 400 TAF consistent with its flood control diagram. This meant that storage had to stay at or below 577 TAF which, it did for much of the month. To achieve this, however, required considerable releases and abstractions, with total losses over the month of about 246 TAF. Overall, the reservoir had a net storage loss of about 55 TAF for the month (e.g., average daily storage loss was about 1,774 AF).
Contrast that to Shasta Reservoir operations where, although the reservoir released 175,581 AF over the month (through its powerhouse), reservoir inflow was calculated to total over 467 TAF. This resulted in the reservoir experiencing a net gain of over 290,000 AF (equivalent to a 20.39-foot rise in water surface elevation).
Reservoir releases have been consistent for much of January with releases from Keswick and Folsom dams providing much of the northern California Delta inflow. Keswick Reservoir was averaging about 3,300 cfs and Folsom Reservoir ratcheted down from approximately 5,000 cfs in early January to about 2,000 cfs by the end of the month. In the last several days Oroville Reservoir, which was releasing about 950 cfs for much of the month, increased its releases to 3,000 cfs.
Current reservoir and snow conditions …
My apologies for the random organization of the graphs and charts below. My website appears to be oddly committed to a random organization 🙁 … -Maven
