By Jay Lund
Droughts are strange, and this one is becoming scarier.
February began with a nice few stormy days, but has since looked like this January – very dry. And so far, the March forecast is not wet.
At the beginning of March, the Northern Sierra (Sacramento Valley) Precipitation Index was down to 88% of average to date, although it already almost equals total precipitation for all of 2014 (both good and bad news). For the San Joaquin Valley and Tulare basin (where most water use occurs), precipitation is about half of average for this date – slightly wetter than this time last year. Snowpack is roughly like last year – among the driest on record.
Will March will be as dry? Statistically, little can be said. There is little correlation in monthly precipitation during Northern California’s wet season, but droughts are inherently unusual. The forecast and climate conditions so far look dry.
The best news is a bit more overall reservoir storage than last year at this time (but still about 5 maf below average for this time of year). The big reservoirs in the Sacramento Valley have 1.3 maf more than last year at this time – this is the good news. South of the Delta surface storage is about the same overall, but differently distributed. San Luis reservoir, which serves the west side of the valley and southern California is about 600 taf higher, but the large reservoirs on the San Joaquin River tributaries are about 600 taf lower.
Groundwater storage is probably about 6 maf less than last year.
Without a miracle March, we will have another critically dry year for 2015. Northern California is likely to be a bit better off than last year, but could be about the same (very dry). In the southern Central Valley and southern California conditions could easily be as bad or worse than last year.
The state is likely to protect environmental flows more carefully this year, probably a good thing to reduce potential for more endangered species listings after the drought. The State Water Project has said they expect about 15% deliveries. The federal Central Valley Project has now announced initial 0% deliveries for regular agricultural water contracts, likely cutbacks (of 25%?) for water right exchange and settlement contractors, and 25% urban deliveries for 2015. While these percentages might improve in the remaining month of the wet season, there is a good chance that water allocations will be similarly dismal to 2014, with less groundwater available in some parts of the state.
Fortunately, some Northern California reservoirs have more storage than a year ago, while reservoir levels elsewhere are more mixed. Overall, we remain about 6 million acre-feet below average for reservoir storage this time of year. In the southern Central Valley, west side reservoirs (San Luis) have much more water than last year, but the east side tributaries to the San Joaquin River are very low (Exchequer at 8% of capacity).
Aquifer levels will generally be lower than a year ago in the areas highly dependent on groundwater.
Snowpack is truly sad, about 16% of average for this time of year.
The 2014 water year ended at 60 percent of average annual precipitation for Sacramento Valley. For 2015, we’re already about at this total, so 2015 is very likely to be at least a bit wetter than 2014 for the Sacramento Valley. A very wet March and early April sure would help.
Both the San Joaquin and Tulare basins are slightly wetter than this time last year. 2015 could be better than 2014, but could also easily be drier.
The difference between a drought and a wet year in California is just a few storms. We are at two significant storms so far, mostly in the northern state. There is little time left to make this up, particularly south of the Delta.
Sadly, our standard for 2015 is not average, but the miserable conditions of 2014. That’s how dry it is.
Beware the dries of March.
Jay Lund is a professor of civil and environmental engineering and director of the Center for Watershed Sciences at UC Davis.
The links above can help keep you up to date. For more data, explore the California Department of Water CDEC web site http://cdec.water.ca.gov.
Lund, J. “The California Drought of 2015: January” California WaterBlog. Jan. 5, 2015
Lund, J. and J. Mount. “Will California’s drought extend into 2015?” California WaterBlog. June 15, 2014
Swain, D. “The Ridiculously Resilient Ridge Returns; typical winter conditions still nowhere to be found in California” California Weather Blog. Feb. 16, 2015