Prepared exclusively for Maven’s Notebook by hydrologist Robert Shibatani
From a water resources and supply perspective, February was dismal. Monthly precipitation totals at the primary reservoirs across the State were essentially zero. Accordingly, accumulated precipitation percent of averages are dropping below normal with the exception of upper American River basin at Blue Canyon, which still has precipitation totals at 109% of average.
The Northern Sierra Precipitation – 8 – Station Index stands at 31.9 inches which is 89% of average (i.e., 36 inches) for this date. For the San Joaquin Precipitation – 5 – Station Index, the current 20.4 inches is about 77% of average (i.e., 27 inches) for this date. For the Tulare Basin Precipitation – 6 – Station Index, the current 13.5 inches is 72% of average (i.e., 18 inches) for this date.
Statewide, across 104 snow measurement stations, averaged SWE stands at 15.5 inches which is about 64% of normal for this date. Statewide SWE stood at 92% of normal only a month ago. Across the northern, central, and southern regions, SWE values range between 53-58% of the April 1st average and between 60-67% of normal for this date, all indicative of the significant SWE loss occurring during this past month. In the central region, averaged measured SWE is at its highest, relative to other locations at 17.0 inches.
CVP reservoir storage as of yesterday was 4.57 million acre-feet (MAF) or approximately 63% of its 15-year average. Reservoir storage is 38.5% of total system capacity. Oroville Reservoir storage stands at 1.66 MAF representing 87% of its 15-year average. Storage levels at the large federal reservoirs, Shasta, Trinity, and New Melones are low, measuring 1,690,000, 787,000, and 983,000 acre-feet, respectively. These storage numbers as a percent of each of their 15-year averages are worrisome; 57% for Shasta, 53% for Trinity, and 69% for New Melones.
System reservoir releases have been steadily increasing in response to downstream regulatory requirements. Flood encroachment is still an operational priority at all State and federal reservoirs and Oroville Reservoir it seems has taken on a larger responsibility for meeting downstream flow requirements, relative to past years. For example, it has been recently releasing 4,500 cfs, when its historic median for this time of year is 1,750 cfs.
North Delta flow is typically made up of the “big three”, outflow from Shasta, Oroville, and Folsom. The average daily Sacramento River flow at Freeport over the month was 12,387 cfs; 83% of that flow coming from releases from the aforementioned reservoirs. Delta inflow as a daily total, averaged 14,488 cfs, the remainder coming from San Joaquin River flows, East Side streams, and Yolo. Total Delta daily exports during February averaged about 1,900 cfs, leaving a Delta outflow (as a 7-day average) of 11,084 cfs. The average daily E/I ratio was 13%.
There is no doubt the system could use additional carryover. Is a “Miracle March” on the horizon? At the moment it doesn’t look promising. There is some rain forecast for later this week and scattered rain around mid-month, but nothing substantive on the radar.