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.
Four 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.
On April 1, 2015, for the first time in 75 years of early-April measurements, DWR found no snow at the Phillips snow course. The water content in the snowpack at that Sierra Nevada location was zero. For the latest on the April 2015 snow survey: http://www.water.ca.gov/news/newsreleases/2015/040115snowsurvey.pdf.
Governor Edmund G. Brown Jr. directed first- ever statewide mandatory water reductions. Governor Brown called for mandatory water reductions in cities and towns across California to reduce water usage by 25 percent. This savings would amount to approximately 1.5 million acre-feet of water over the next nine months, or nearly as much as Lake Oroville now holds. View the executive order here: http://gov.ca.gov/news.php?id=18910.
The State Water Project, which supplies 25 million Californians, anticipates being able to provide only 20 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 Save Our Water.
Statewide precipitation data.
Sierra snowpack accounts for one-third of the state's water supply