Prepared Exclusively for Maven’s Notebook by Robert Shibatani
The much-anticipated storms of February have come and gone. Despite early optimism, the storms were modest at best, providing only temporary hydrologic relief. Precipitation and accumulated reservoir inflows-to-date as well as current reservoir storage remain below average.
Overall north CVP storage stands at 5,922 TAF representing about 52% of total system capacity (due to required seasonal empty space flood storage requirements) and 82% of the 15-year average. Trinity, Shasta, New Melones, Folsom and San Luis reservoirs are at 82, 74, 104, 72 and 59% of their 15-year averages, respectively. All reservoirs gained storage over the month of February, some from direct precipitation and quickflow (both rainfall and snowmelt) and some from accumulated baseflow. Storage gains for the month of February through the 27th for these same reservoirs were 24,300, 144,700, 500, 55,500, and 123,969 AF respectively. (NB. Reservoirs can physically gain storage while having their % of average values decline; this depends on the historical storage pattern) Oroville Reservoir storage stands at 1,342 TAF, which is about 38% of full capacity and represents approximately two-thirds of its 15-year average storage for this time of year.
Even with annual precipitation totals benefitting from February’s storms, Statewide precipitation remains well below average. Trinity and Shasta in the north are 62% and 44% of average, respectively. In central California, Blue Canyon and New Melones are 57% and 73% of average, respectively. The Northern Sierra Precipitation – 8 Station Index stands at 18 inches or 50% of average for this date. This is identical to last year on this same date. The San Joaquin Precipitation – 5 Station Index stands at 14.1 inches or 52% of average. For this date, the San Joaquin Precipitation Index exceeds the last two water-years as well as WY 2014-2015. The Tulare Basin Precipitation – 6 Station Index stands at 7.6 inches or 39% of average.
As evidence from widespread news coverage, snow accumulations benefitted from February’s storms. Statewide, average current snow water equivalent (SWE) increased to about 15.1 inches as of February 25th. And yet this only represents about 54% of the April 1st average and around 64% of the seasonal average to date. The central Sierra Nevada SWE is 17.7 inches (or 71% of normal and 60% of its April 1st average) while the northern Sierra Nevada/Trinity region SWE is 16.3 inches (or 66% of normal and 57% of its April 1st average). Snow accumulations from this month’s storms have definitely helped and may represent our seasonal water savior; but overall totals still remain below average.
At this point a “Miracle March” seems unlikely, however, established carryover levels while concerning are not indicative of “extreme” drought conditions as suggested by some. Releases have been monitored closely this year and continually prescribed judicious discharges (e.g., below average releases at Oroville and Folsom) now, will inevitably help later this spring and summer.
Prepared by Robert Shibatani
Robert Shibatani, a physical hydrologist with over 35-years combined experience as an international expert witness on reservoir-operations, climate change hydrology, commercial flood damage litigation, and water supply development. He is Managing Partner for The SHIBATANI GROUP International, a division of The SHIBATANI GROUP Inc. and resides in Sacramento, California. firstname.lastname@example.org