Storms, Drought and California's Water Situation: Key Points
January 29, 2015
Three main sources of water sustain California – mountain snowpack, water stored in reservoirs and water pumped from underground aquifers. All are connected, and when the Governor declared a drought emergency on January 17, 2014, all three had been depleted by an extended dry period. The Sierra Nevada snowpack stood at 14 percent of normal for the date. The state's two biggest reservoirs held less than 40 percent of their capacity, and aquifer levels from Siskiyou County to San Diego County were in decline.
Three consecutive dry years have left millions of acre-feet of empty space in reservoirs across California. That space cannot be filled by several typical winter storms or even one particularly powerful storm. DWR's state climatologist estimates that 150 percent of average precipitation for all of Water Year 2015 would be needed for California to have a good chance at exiting the drought.
A series of December storms, including an atmospheric river, caused rain to fall heavily in many California locations nearly three months into Water Year 2015. However, the storms did not immediately result in normal or above normal conditions in most of the state's water basins, and nearing month's end, January 2015 was shaping up to be the driest start of the year in California's weather records. The absence of rain has increased the likelihood that California's drought will extend into its fourth consecutive year and last throughout 2015.
The abrupt increase in storage within California's major reservoirs due to December's rain was followed in January by a leveling of those increases, and some large reservoirs, such as Lake Folsom, recorded decreases in the amount of water in storage from one day to the next on some occasions during January. Shasta Lake, California's largest reservoir, held 66 percent of its historical average on December 31, but by late January, that percentage was only 65 percent due to January's meager precipitation. Lake Oroville, California's second-largest reservoir, held 62 percent of its historic average at year's end, and that percentage remained static through January. On January 29, Oroville held about 1.44 million acre-feet (AF); the long-term historical average for that date is 2.32 million AF.
The December storms did not favor Central California's reservoirs nearly as well as they did those in the north. Reservoir storage on the San Joaquin River and its tributaries is critically low. Exchequer reservoir on the Merced River can hold more than one million AF, but at the end of 2014, its storage stood at about 73,000 AF feet – 7 percent of total capacity and 16 percent of its historical average for late December. The reservoir's storage continued to decline, and by late January, Exchequer held about 65,000 AF, just 6 percent of its capacity and 13 percent of its historical average.
The water content in the Sierra Nevada snowpack – as described in the next section, below -- was about half of its historical average in late December and only 25 percent of average by late January. That's better than when the Governor declared a drought emergency nearly a year ago, but it's still insufficient to refill reservoirs or meet demand as the snowpack melts during the late spring and summer.
Refilling reservoirs and rebuilding the snowpack throughout the state would require a series of colder storms through February and March, and recharging the state's aquifers would require even more precipitation and time. Although DWR monitors reservoir and snowpack conditions continuously, we will not have a good estimate of next year's water supplies until April. The weather outlook provides no indication that storms will benefit California particularly well in the months ahead. The chances are just as good for dry weather as for wet.
Californians have responded positively to the Governor's call for water conservation, and that call remains unchanged now that the drought appears to be in its fourth consecutive year. The State Water Project, which supplies 25 million Californians, anticipates being able to provide only 15 percent of the supplies for which its customers contract in 2015.
The quickest, most effective way to save water now is to curb landscape irrigation. Shut off sprinklers. Plants get all the moisture they need from rain and will for weeks to come. For drought news, visit drought.ca.gov. For more ways to save water, visit saveourwater.com.
Dry Conditions Continue into 2015
Calendar Year 2014 was California's driest year in records dating to the 1800s, and water conditions four months into a new water year (October 1, 2014 through September 30, 2015) suggest the state's drought is pushing into its fourth consecutive year. In most years, California receives about half of its precipitation in the months of December, January and February, with much of that precipitation falling as snow in the Sierra Nevada Range, but so far, snowfall has been far below normal.
A handful of large winter storms can make the difference between a wet year and a dry one. In normal years, the snowpack stores water during the winter months and releases it as it melts in the spring and summer to replenish rivers and reservoirs. However, those storms did not arrive during Water Year 2014, and relatively dry weather reduced the amount of snowpack in California's mountains. Each of that water year's five snow surveys – conducted near the first of the month from January through May – found a statewide snowpack water equivalent (WEQ) far below average for the dates of the surveys. On May 1, the snowpack's statewide average WEQ was only 4 inches, just 18 percent of the historical average on that date.
Snow scarcity has continued in Water Year 2015. The first manual survey of the season on December 30, 2014 found just 4 inches of WEQ at the Phillips station snow course 90 miles east of Sacramento. That was just 33 percent of the course's historical average of 12 inches at that site on December 30. Similarly, the statewide WEQ reading at the end of December was only about 50 percent of normal. The second manual survey conducted at the Phillips snow course on January 29 found even less snow – 2.3 inches of WEQ, which was 12 percent of the late-January historical average.
This snow scarcity has serious implications for California's drought, because much greater than average precipitation must fall as rain and snow for California to exit the drought. By the end of calendar year 2014, rainfall had indeed been above average in Northern California watersheds due to a series of early-December storms, including an atmospheric river – the so-called "Pineapple Express" – that produced considerable rainfall. But January was exceptionally dry throughout the state, with the northern two-thirds of the state receiving less than 25 percent of average rainfall. About half of that area recorded less than 5 percent of its normal precipitation.
Despite the December storms, the 8-station northern Sierra precipitation index had fallen to less than 90 percent of its historical average by late January. Precipitation at the five stations in the San Joaquin region was only 46 percent of normal by late January; similarly, the six stations in the Tulare Basin registered precipitation at only 49 percent of normal.
Collectively, California's water conditions are moving in the wrong direction for the state to exit the drought. DWR's state climatologist estimates that precipitation would have to be 150 percent of average for the entire water year that ends on September 30, 2015 for California to have a good chance at ending the drought this year.
Despite the poor precipitation record so far in Water Year 2015, Mother Nature may surprise us yet. About half of the years with dry first quarters in the historical record of northern Sierra precipitation caught up to average by the end of the water year. But as noted by DWR's climatologist, a normal precipitation year would not be enough to restore groundwater and surface reservoir storage and overcome low soil moisture. California needs an exceptionally wet year to be made whole. In the meantime, Californians are urged to continue their positive response to the Governor's call for conservation. It's as important in 2015 as it was last year.
Current Water Conditions
- • California Drought – U.S. Geological Survey - New
- • Drought Response – Groundwater, April 2014
- • 2014 Drought Operations Plan
- • Daily Drought Information Summary
- • Klamath/San Joaquin/Sacramento Hydroclimatic Reconstructions from Tree Rings
- • Tree Ring Report Appendix.zip (data files)
- • ACWA Launches Interactive Map Showing Local Response Actions
- • Cal OES Drought Page
- • Governor's letter, Interagency Drought Task Force
- • DWR-CSUF Agricultural Drought Preparedness Workshop
- • Experimental Seasonal Forecast
- • Experimental Seasonal Forecast Presentation