Prepared by Robert Shibatani exclusively for Maven’s Notebook

September 30, 2020

The 2019-2020 water-year (WY) is drawing to a close.  At this time of year, it is always informative to see where we ended up storage wise across the CVP and SWP as the new 2020-2021 WY commences and the hydrologic “clock” get reset.  Where are we in terms of CVP/SWP water supply?

Despite precipitation to date totals across the State being substantially below average (e.g., Shasta, Trinity, and Blue Canyon being 55, 64, and 59% of average), total north CVP reservoir carryover storage is 99% of its 15-year average.  In other words, we’re starting the 2020-2021 WY about where we should be storage wise.  Compared to the 2018-2019 WY, however, total north CVP storage this past WY was only approximately 68% of the previous year.  Overall storage across these reservoirs was about 5.88 MAF or 52% of the reservoir’s total system capacity.

New Melones seemed to do the best, finishing at about 112% of its 15-year average.  The other three largest reservoirs, Shasta, Oroville and Trinity finished the WY at 91%, 96% and 97% of their 15-year averages, respectively.  Each of these reservoirs were able to accomplish this despite their accumulated inflows being notably below their 15-year averages.  Shasta, Trinity, New Melones and Folsom reservoirs, for example, received 63%, 39%, 60% and 57% of their 15-year average accumulated inflows, respectively, over the past WY.  Judicious water operations allowed reservoir managers to build-up carryover despite depressed inflows.

Moving forward through the Fall, while a La Niña climate pattern has been slowly developing over the summer, how it might translate into upcoming precipitation totals remains uncertain.  After all, a La Niña isn’t the “only player in the rainfall prediction game”.  Increased precipitation is possible across northern California while warmer, drier, and less stormy conditions could easily unfold in the south.

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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