Prepared exclusively for Maven’s Notebook by Robert Shibatani

The first major storm of the season passed through last week providing much needed hydrological relief over much of the State and, in several coastal areas, a little too much.  But reservoirs, particularly federal and State reservoirs benefitted considerably.  Overall north CVP storage has recovered to 85% of the 15-year average which had dropped to 77% earlier in the month with Trinity, Shasta, New Melones, Folsom and San Luis reservoirs recovering to 86, 78, 109, 70 and 66% of their 15-year averages, respectively.  Oroville Reservoir stands at 68% of its 15-year average.  Total storage in CVP reservoirs and Oroville is about 6.86 MAF representing about 44% of the total CVP and Oroville storage capacity.

Snow accumulations have rebounded somewhat across the State with this latest storm.  Statewide, average current snow water equivalent (SWE) is about 11 inches (gaining about half a foot from a month ago).  This represents about 39% of the April 1st average and around 66% of the seasonal average to date.  The central Sierra Nevada SWE is 13 inches (or 71% of normal) while the northern Sierra Nevada/Trinity region SWE is 11.2 inches (or 64% of normal).

Even with last week’s storms Statewide precipitation totals remain well below average. Trinity and Shasta in the north are 53% and 40% of average, respectively.  In central California, Blue Canyon and New Melones are 58% and 82% of average, respectively.  The Northern Sierra Precipitation – 8 Station Index stands at 14 inches or 51% of average for this date.  The San Joaquin Precipitation – 5 Station Index is doing a little better, relative to other years.  Its Index stands at 12.4 inches or 61% of average as well as already exceeding the cumulative total for last year and the driest year on record for this date.

With precipitation totals remaining around 50% of average, releases continue to be judiciously made. There have been no encroachment required “spills” from any of the primary CVP or SWP reservoirs. Barring any large unforeseen late season storm systems, flood releases seem a low probability at this time.

Another weaker system is set to hit the Sierras today and tomorrow with another long-range mid-month storm projected.  The State is still well below its hydrologic metrics for this time of year and the next two months will be critical to establish our seasonal carryover. 

Prepared by Robert Shibatani

Robert Shibatani, a physical hydrologist with over 35-years combined academic, legal, consulting and water advisory expertise, is 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.


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