Los Altos Weather – Dry, Warm March

Continuing my monthly weather posts, March was warmer and drier than normal in Los Altos, California, as California’s drought stretches into the fourth year. Landscaping needs more water than usual due to the warm, dry weather. Despite calls to reduce water consumption, it’s hard to stop watering drought-stressed trees and shrubs that took years to grow. With the warm winter, I was concerned that our fruit trees didn’t receive enough winter chilling, but this morning’s photo of our pluot tree shows that fruit has set.

Acknowledging that there’s not end in sight for the drought, California’s governor issued an executive order designed to reduce urban water usage by 25%. Although much needed, almost all the measures will take months to significantly reduce water usage. Meanwhile, the State and County asked for a 20% reduction in water use a year ago, but our county conserved 13% in 2014 and 4% so far in 2015. Even if we achieve the 25% savings this year, we’ll continue overdrafting the aquifer beneath our valley.

My home town of Los Altos in the San Francisco Bay Area received .16 inches of rain in March, much less than the average of 2.49 inches.

Negligible rain in March
Negligible rain in March

We live in an arid region, and we received only half the normal rainfall since January 2013. Our drought continues.

Received half the normal rainfall since Jan. 2013
Received half the normal rainfall since Jan. 2013

We can draw two conclusions from the above data.

First, next year might be worse than this year. Our rainfall since July 2014 is nearly normal — 88%. The coming year could be drier than the past year’s nearly normal rainfall.

Second, our recent rainfall indicates much more variation in rainfall than we expected. Almost all our rainfall in the past 12 months came in two series of storms: one in November-December, and the second in February. If the storm door hadn’t opened twice, we would have had a very dry year. Our annual rainfall depending on two weather events illustrates the variation in our rainfall. As documented in The West Without Water, California has suffered much longer droughts and floods in our prehistory, so we need to prepare for weather beyond the history of the past century that has had mild weather. Despite what we want, California is inherently an arid region subject to megadroughts and floods.

As shown below, March was warmer than normal, continuing the trend. The combination of little rain the past four months and above-normal temperatures increases the drought stress on plants. It’s hard to conserve water when your trees and shrubs that took years to grow need water.

March was warmer than normal
March was warmer than normal

Executive order for mandatory 25% water use reduction

On April 1 (no fooling!), California’s governor signed an executive order imposing “restrictions to achieve a statewide 25% reduction in potable urban water usage through February 28, 2016.” The executive order has 31 actions. Here are some highlights:

  • Achieve 25% water use reduction compared to 2013. A year ago, the Governor and County Board called for a 20% reduction. Our County reduced water use by 13% in 2014, and our water use for the first two months of 2015 is up 4% from 2013. Changes are required to dramatically change our water use and achieve a 25% reduction.
  • “Areas with high per capita use achieve proportionally greater reductions than those with low use.” About half of California’s urban water is used for landscaping. Cities with larger lot sizes have more landscaping and generally use more water per capita than cities with smaller lot sizes. Los Altos has larger lots than most nearby cities, and our water utility has higher per capita water usage than most surrounding cities. Do Los Altos customers use more water? Our city has had the data for months but has not made this data public.
  • “Replace 50 million square feet of lawns and and ornamental turf with drought tolerant landscapes.” Lawns require a lot of water, fertilizer, and herbicides. Reducing lawns or replacing them with drought tolerant plants will save water every year, but the process of planning and replacing a lawn takes months.
  • “Require that commercial, industrial, and institutional properties, such as campuses, golf courses, and cemeteries, immediately implement water efficiency measures to reduce potable water usage”.
  • “Prohibit irrigation with potable water outside of newly constructed homes and buildings that is not delivered by drip or microspray systems.”
  • “Direct urban water suppliers to develop rate structures and other pricing mechanisms, including but not limited to surcharges, fee, and penalties, to maximize water conservation consistent with statewide water restrictions.”

The actions in the executive order look reasonable. It’s great that the state took a strong leadership role, but this was necessary. Our water wholesalers and retailers are paid based on water use, so their taking strong measures to promote water conservation reduces their income in the short run.

We’ll soon start the long, dry summer of our Mediterranean climate. How long will it take for counties, cities, and water retailers to put these measures in place and educate the public. so that water use drops significantly? Campuses, golf courses, and cemeteries are ordered to immediately curtail their water usage by 25%. Most measures will take months to significantly reduce water usage. Banning the watering of lawns would produce immediate savings. Some cities did this in prior droughts, but the executive order stopped short of this.

The executive order is a great first step, but reducing water use will be an uphill battle. A year ago the State and County asked for a 20% reduction in water use. Our County conserved 13% in 2014 and 4% so far in 2015.

How long before the risk of permanent land subsidence resumes?

We’re entering our dry summer, so we’ll probably have to make do with the water we have until the end of the year. Based on historical averages, November is the next month with more an inch of rain.

Santa Clara County is overdrafting the aquifer that we live on, and this overdraft will probably continue. The water utility serving Los Altos used 50% groundwater in 2014. Even if we reduce water usage by 25%, this is still much less than the 50% groundwater used last year. With a record-low snowpack, water imports probably won’t increase dramatically this year, so overdrafting will probably continue.

The time remaining before the cumulative overdrafts cause the valley to resume sinking permanently depends on the amount of water in the aquifer and how fast we overdraft the water.

The 2015 Protection and Augmentation of Water Supplies Report shows the groundwater remaining before permanent land subsidence is at risk. This table from the report shows that about 260,000 acre-feet of water remain at the end of 2014, down about 80,000 acre-feet from the year before.

2014 EOY Groundwater Storage
2014 EOY Groundwater Storage

One way to project the future is to use historical actuals. That is, if 2015 turns out to be like 2014, then the 2015 will see the same change in storage as 2014. The end-of-year 2014 groundwater storage was about 260,000 acre-feet (AF), and the groundwater storage was overdrafted by about 80,000 AF in 2014.

Projecting the 2014 overdraft into 2015, the groundwater storage at the end of 2015 would be about 180,000 AF. This projection incorporates the near-normal rainfall and 13% conservation rate in 2014. If we conserve more than the 13% rate in 2014, we’d have more water in the aquifer. If we get less rain in 2015 than the near-normal rainfall in 2014, we’d have less groundwater.

Groundwater pumping and managed recharge are the two primary factors for overdraft. Our 2015 experience so far is similar to the 2014 actuals. Managed recharge is the water that we pump into man-made basins to sink into the ground and the aquifer. As shown below, groundwater pumping and managed recharge in early 2015 are about the same as for 2014 — higher-than-normal groundwater pumping that’s much higher than the below-normal managed recharge.

Groundwater pumping
Groundwater pumping
Managed recharge
Managed recharge of groundwater

In March the County Water District staff presented these four projections to the Board.

2015 Water Supply Projections
2015 Water Supply Projections from District staff

Projection A has about the same year-end groundwater storage as my actuals projection , but projection A assumes no reduction achieved while the actuals projection incorporates last year’s 13% reduction.

Projections C and D say that the groundwater storage will increase in 2015 — we’ll recharge more groundwater than we pump. But we overdrafted 80,000 acre-feet last year, we’re pumping and recharging groundwater like last year, and the drought has no end in sight.

Time will tell which projections are more accurate, and that’ll better inform us of how long we have before land subsidence is a risk.


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I enjoy travel, art, food, photography, nature, California native plants, history, and yoga. I am a retired software engineer. The gravatar is a Nuttall's woodpecker that visited our backyard.

One thought on “Los Altos Weather – Dry, Warm March”

  1. We were worried about lack of Spring rain in our area and we are supposed to get one of the highest rainfalls which source some great rivers. But it has rained a little later than usual. Patterns seem to be changing.


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