The story of December is our heavy rains. The storm door opened in November and stayed open through mid-December. We received 8.5 inches of rain in December, three times higher than normal and three times higher than for any month in the past two years. But we’re still behind on rainfall, and the state’s reservoirs and groundwater are still low due to the 3-year-old drought.
The US National Weather Service expects that the drought to continue. In our town of Los Altos, we use over 50% more water per person than many nearby cities. To meet user demand, we are overdrafting our valley’s aquifer, and the major state aquifer is being overdrafted 2.5 trillion gallons a year during the drought.
Los Altos Weather
The story of December is our heavy rains. The storm door opened in November and stayed open through mid-December. We received 8.5 inches of rain in December, three times higher than normal and three times higher than for any month in the past two years. But the state’s reservoirs and groundwater are still low due to the 3-year-old drought.
Despite all that rain, we’re still way behind in rainfall. Rainfall for the past two years is 57% of normal, so much better than the 34% of normal at the beginning of December.
The storms came from the south, so our overnight lows stayed warmer than normal. We had no killing frosts in December, which is unusual. Our cherry tomato plant was bearing tomatoes through Christmas.
In an update following our December rains, the US Weather Service expects California’s drought to remain but improve.
Los Altos has higher residential water usage than most surrounding cities
Los Altos residential customers use much more water than most South Bay cities, based on residential water usage data collected by the California Water Board. The Pacific Institute displays the state usage data on the map below. Los Altos (dark yellow near the bottom of the map) uses over 150 gallons per day per person, while many surrounding communities (green) use less than 100 gallons per day per person.
California Water customers, which includes Los Altos, uses upwards of 50% more water per person than in many neighboring cities, such as Mountain View, Sunnyvale, and San Jose. The Pacific Institute noted that “water use tends to be higher in … in suburban areas with more outdoor landscaping and lawns”, and this is probably true for Los Altos.
To water our outdoor landscaping and our lawns, our Santa Clara Valley imports water from the Sierra Nevada Mountains, but that watershed is pumping groundwater at an unsustainable rate that has caused land subsidence.
Source of the valley’s imported water has groundwater overdraft of 2.5 trillion gallons a year during drought
The Santa Clara Valley imports water from the Sierra Nevadas, which drain into the Central Valley. This watershed is sadly oversubscribed and has been sinking for years. This NASA study found that the groundwater under the Central Valley has been overdrafted by 2.5 trillion gallons a year during our three-year-long drought.
It will take about 11 trillion gallons of water (42 cubic kilometers) — around 1.5 times the maximum volume of the largest U.S. reservoir — to recover from California’s continuing drought, according to a new analysis of NASA satellite data.
GRACE data reveal that, since 2011, the Sacramento and San Joaquin river basins decreased in volume by four trillion gallons of water each year (15 cubic kilometers). That’s more water than California’s 38 million residents use each year for domestic and municipal purposes. About two-thirds of the loss is due to depletion of groundwater beneath California’s Central Valley.
Santa Clara Valley relies on imported water to prevent further land subsidence here
If our valley didn’t import water, land subsidence would resume in our valley. Shown below, the town of Alviso sank below sea level before water imports started in the 1960s. This levee protects Alviso from flooding, but the levee would sink if land subsidence starts again.
Through November, we overdrafted the valley aquifer by nearly 100,000 acre-feet of water in 2014. Although user demand has dropped less than 20% due to water conservation efforts, sharply curtailed managed recharge and higher-than-normal groundwater pumping caused the large overdraft. If the drought and overdrafts continue, land subsidence will resume at some point. How close are we?
Valley aquifer overdrafted by nearly 100,000 acre-feet this year