Water Supply Outlook Slips
At a glance, some of the key ingredients in the making of this year’s Friant Division water supply don’t look bad. February 1’s average San Joaquin River watershed snowpack was measured at normal levels. The season’s initial “most probable” outlook for natural San Joaquin River runoff during the peak runoff period is just below average for early February.
Looks, however, may be deceiving.
What appeared to have the makings of at good central Sierra water supply season when the new year dawned has dried into a less optimistic outlook as a result of mostly arid and cold weather since early January. Little overall change is predicted.
This year’s first California Department of Water Resources runoff forecast sees unimpeded San Joaquin River discharge (as if there were no dams) of 90% of average – 1,130,000 acre-feet – at Friant during the key April-through-July snowmelt period.
That prediction assumes average amounts of precipitation will occur in the coming months but, except for a modest February 7-8 storm that brought fairly light snow amounts to low elevations and showers across the valley, there has been almost no significant storm activity since the holiday season.
Thus, DWR’s outlook suggests that the April-July period could produce as little as 770,000 acre-feet of San Joaquin River runoff, just 61% of average. In 2012, 558,917 acre-feet (44% of average) of runoff was generated by the San Joaquin’s melting snowpack during a very dry year.
DWR has dropped the southern San Joaquin Valley’s overall 2013 outlook into a “dry year” classification.
The bottom line, when the U.S. Bureau of Reclamation makes its first Friant Division water supply declaration, is likely to be an amount that again falls below Friant’s average deliveries of Central Valley Project water. Reclamation is expected to make its initial CVP supply declarations February 15. Bureau officials typically rely upon the lower-end forecast – which is statistically expected to be exceeded 90% of the time – in declaring Friant’s water supply availability during winter and spring months.
Friant’s water supply for the contract year that will end February 28 remains declared by the Bureau at 57% (456,000 acre-feet) in districts with Class 1 contracts. No Class 2 water has been available since 2011.
In an average year, about 1,250,000 acre-feet of Central Valley Project water is delivered to users along the Madera and Friant-Kern canals.
“Although the water year started out very strong, a dry January has reminded us that hydrologic conditions in the region can change quickly,” David Murillo, Reclamation’s Mid-Pacific Regional Director, said during a recent CVP water users conference in Reno, Nevada.
SNOW SURVEY RESULTS
The season’s first full San Joaquin River watershed snow survey of 17 courses showed snowpack water content readings averaging 100% of normal for February 1, but that represents a sharp decline from 143% of the January 1 snowpack average measured on a limited number of courses.
Snowpack water content ranged from a high of 31 inches at Chilkoot Meadow, a course at the 7,150-foot elevation in Madera County, to just 3.6 inches at 7,200-foot Florence Lake.
Greatest of all snow depths was 63 inches at 8,000-foot Nellie Lake above Huntington Lake. Florence Lake, with 11.9 inches, had the least snow on the ground,
California’s typical water supply fickleness has been evident in fairly radical precipitation swings that have occurred since fall.
The DWR noted that during December, 11 major rivers flowed at a rate greater than 200% of average, contributing to a statewide average of about 190% of normal.
In January, however, no major Sierra rivers flowed at a rate greater than 75% of normal and the statewide average was about 40%. January flows in the Sacramento River, San Joaquin River and Tulare Lake regions were 45-46% of average.
A San Joaquin region five-station precipitation index had amounts of 134% of average in November and 185% in December, only to fall to 1.3 inches – just 17% of the historic monthly average – in January