Prepared Exclusively for Maven’s Notebook by Robert Shibatani

Summer is officially only 3 weeks away, but it looks like we are heading straight into another drought year.  Warnings and reports of another drought are being echoed across agency, media, and public circles. The pressing questions now are how damaging might this drought be, what are some its broader water resources and delivery implications and, how protracted could it become?

As of yesterday, north CVP storage stood at 5.264 MAF or 46% of total north CVP capacity (e.g., the first-time this year WY that active storage dropped below 50% of total capacity).  North CVP storage decreased by 551,000 AF during the past month.  Current storage in CVP reservoirs represents about 65% of the 15-year average.  Water storage in Shasta, Folsom, San Luis, and Oroville reservoirs are well below their 15-year averages at 56, 46, 55, and 53%, respectively.  Only New Melones, Trinity and, surprisingly, Millerton, are at more “comfortable” storage levels for this time of year (e.g., 92, 72, and 72%, respectively).  While the talk has been about reservoir storage decline, the most notable coming from Shasta Reservoir which lost 304,000 AF over the month, some reservoirs were still gaining storage.  Traditionally low Millerton Lake gained over 40,000 AF, Tulloch increased storage by 4,141 AF and even Folsom Reservoir, gained 2,100 AF over the month.

We have been watching reservoir releases closely over this past month.  No peculiar releases have been observed.  All releases have been below or well within the acceptable 15-year median range.  Additionally, there were no critical emergency conditions that arose which required significantly ramped up releases during the past month.

Precipitation totals over the past month were trace to non-existent.   Cumulative WY totals to date are around one-half of their long-term averages with stations at Trinity, Shasta, Blue Canyon, New Melones, and Huntington Lake showing totals at 54, 40, 49, 63 and 44% of average.  Despite the light Sierra Nevada snowfall of a week ago (that actually threatened to close some passes), overall warm temperatures throughout the month acted to rapidly depleted SWE across the State.  As of yesterday, Statewide SWE was effectively zero.

This Memorial Day weekend ended with the first heat wave of the season; temperatures across the Capitol region topping 104°F.  Past records have shown that precipitation can and has occurred during June, but current forecasts do not show any potentially threatening systems moving in any time soon.  By the July 4th Holiday weekend, we should have a markedly better idea of how we will weather the peak summer months through to the end of this WY.

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.

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