Worried about how climate change will affect rainfall in the coming decades, some San Luis Obispo residents are calling on the city to stop allowing developers to build new homes — at least until the city recalculates its future water supply.
“We want everybody to take a timeout and stop giving out permits until we actually have reassessed, maybe by June, what our water shortage contingency plan is ... and look at climate models,” resident Allan Cooper said. “And then we say let’s remove it and go back to business — but it won’t be business as usual (with) new insight.”
Cooper is among the residents lobbying the city out of concern that San Luis Obispo won’t have enough water in the future to serve the current population of 46,730 — much less the 56,686 residents who could live in San Luis Obispo by 2035, according to an estimate in the city’s General Plan.
Their worries are exacerbated by the number of large residential developments making their way through the city planning process: 720 homes at Avila Ranch, up to 500 homes at San Luis Ranch, and a plan for up to 275 houses and apartments plus a continuing care retirement facility along Los Osos Valley Road, to name a few.
“To approve any development before we receive assurances that there is enough water is inappropriate,” resident Mila Vujovich-La Barre told the San Luis Obispo Planning Commission during a recent preliminary review of Avila Ranch.
City officials say they are consistently updating their computer modeling to estimate San Luis Obispo’s projected water supply to account for uncertain climate change, infrastructure issues, siltation and recurring drought, said Aaron Floyd, the city’s deputy director of water in its Utilities Department.
“We’re constantly trying to update that model,” he said. “We really don’t want to run out of water.”
Climate change forecasts
Cooper and resident Bob Shanbrom say water supply projections should not be based on historical rainfall records and current water supply, but on future climate projections, which they don’t believe have been adequately done.
“With global warming the extremes are likely to increase,” Shanbrom said. “Whether or not we should build out should be based on climate projections, not whether or not we have water right now.”
Cooper points to studies concluding that climate change is expected to increase the severity of future droughts and predict a much drier climate in the latter half of the 21st century.
One study by scientists at Columbia University’s Lamont-Doherty Earth Observatory concluded that increasing temperatures and resulting moisture losses will push California into even more persistent aridity. The study found evaporation will overpower any increase in rain in California, leaving more or less permanent drought by the 2060s, interrupted only by the rainiest years.
A NASA study published last year found that increases in human-produced greenhouse gas emissions drive up the risk of severe droughts in the Southwest (including Southern California) and the Central Plains. The study predicted multidecade “megadroughts” of more than 30 years by the end of the century if greenhouse gas emissions aren’t significantly reduced.
“In general, we expect in Southern California overall precipitation to decline,” Ben Cook, lead author of the study and a climate scientist at NASA’s Goddard Institute for Space Studies and the Lamont-Doherty Earth Observatory, said in a phone interview.
But, he added: “Once you start to get up to San Luis Obispo and further north, it gets a little more fuzzy what the models are saying. Some models say more precipitation in the future, and some say less. I would say that over the next several decades, maybe 20 years, we could see the signs of precipitation starting to decline.”
However, he added, even under extreme climate change scenarios, “there is water out there, but it’s a question of what can we use that water for and is that water in the right location.”
Heather Cooley, water program director for the Oakland-based Pacific Institute, which works to create and advance sustainable water policies, said future models consistently predict higher temperatures in the future.
Precipitation models are more uncertain, “but they are all in agreement that we’re going to be seeing more variability: wetter wet years and drier dry years. We have to plan for a future with more droughts and more floods,” she said.
Communities are just starting to integrate climate change into their supply projections, Cooley said, although the state Department of Water Resources has been including it in its supply and demand projections since 2009 in updates to its California Water Plan.
One chapter on climate change points out that for much of the state’s history, water planning and management relied on past records as predictors of potential future conditions. That is no longer adequate, according to the study.
“Although understanding the past is still an important part of managing for the future, it is becoming increasingly apparent that continued management under this traditional approach will not provide for sustainable water resources into the future,” the report states.
And while water agencies are starting to incorporate climate change information into their planning, more accurate data and analysis is needed to reduce uncertainty and risk in managing California’s future water supply.
In 2010, the state Local Government Commission released the results of a yearlong study examining how climate change is expected to impact San Luis Obispo County: hotter and drier summers, accelerated sea level rise, reduced groundwater recharge.
Predictions for precipitation varied, with two models showing a drier future and one showing a slightly wetter future. But even with substantial increases in precipitation, soil moisture is expected to decline due to increased temperature and evaporation.
According to PG&E meteorologist John Lindsey, the current four-year drought is the driest period San Luis Obispo has seen since 1870, when a weather station at Cal Poly started tracking rainfall.
Examining the models
Floyd said city staff has been looking at some of the climate models, too, while updating its planning using historical rainfall data.
“We’re just trying to figure it out,” he said. “When we look at those models, there’s nothing conclusive that says this is what you should target. So we just build safeguards in and take a very conservative approach.”
In early 2015, the city’s computer modeling was updated to include the new worst-case drought information: rainfall data from 2012-13 and 2013-14, which averaged about 10 inches, according to the city’s 2015 Water Resources Status Report.
The city’s modeling also includes evaporation data from those two years, the current and projected population, citywide water use per capita, the amount of water in Whale Rock and Salinas reservoirs, and the city’s contractual allocation from Lake Nacimiento, Floyd said.
As of the end of January, that model predicted the city has about 3.5 years of water left, though that may be revised because the City Council voted last week to amend its contract to the Nacimiento Water Project to receive an additional 2,102 acre-feet a year. That water would be used during droughts or for short-term needs during infrastructure repairs.
The city is also updating its 6-year-old water contingency plan, which states that new customers and proposed projects would be the last to receive drinking water during any shortages.
Where the city gets its water
San Luis Obispo has four water sources: recycled water (for irrigation) and three reservoirs — Nacimiento, Salinas (Santa Margarita Lake) and Whale Rock — that provide drinking water. The city no longer uses groundwater, but could tap into about 1,000 acre-feet a year if necessary.
In 2015, the city had 10,005 acre-feet of water from those four sources — which will increase to 12,107 acre-feet with the additional water from Nacimiento — and used about 4,900 acre-feet.
An acre-foot is about 325,851 gallons, or enough to serve about three households per year. San Luis Obispo has about 18,000 households.
At the city’s build-out, with an estimated 57,200 people and other anticipated developments, San Luis Obispo would use 7,330 acre-feet a year, according to the water resources status report.
That calculation is based on a citywide use of 114 gallons of water per person per day (for all uses: residential, commercial, industrial, office). This is a conservative number, Floyd said, as actual citywide use is about 92 gallons of water a day.
“What we’re trying to do is have a larger and diverse portfolio of water to account for all kinds of things: siltation, infrastructure issues and a lot of unknowns,” Floyd said. “What we’ve done is built in very conservative or overestimates of how much water usage there will be in the future with new or modern houses coming on line.”
Floyd pointed out that Nacimiento added 13,000 acre-feet just with 1.3 inches of rain received in a previous weekend’s storms.
“We could have done three years of supply in what we got in two days of rain,” he said.
The residents’ group has asked only for a temporary pause in new development, not a long-term moratorium, while the water supply is evaluated using climate change projections. The council has not placed the issue of a moratorium on a future agenda for discussion.
At a council meeting last week, Cooper, Vujovich-La Barre and a few other residents again urged the council to take action.
This time, some council members responded, calling Lake Nacimiento a reliable source and declaring the city in good shape, waterwise. Mayor Jan Marx said she and utilities director Carrie Mattingly have been invited to be on a panel at the third annual California Water Summit in June “because our city is one of the most water-secure cities in the state.”
Councilwoman Carlyn Christianson, who sits on the Nacimiento Project Commission, sounded the most frustrated by the criticism from residents.
“Our city has spent the last 20 years investing millions of dollars to massively increase the amount of water that can come into this city. Nacimiento is a huge source of water,” Christianson said. “When our staff makes a projection ... they do include current climate change. They do include things like wind, water evaporation, drought, lack of rainfall and all those things.
“So this idea that they’re just making up numbers and being very ‘la-di-da,’ not actually using current science and knowledge is an inaccurate statement to make,” she added. “To walk around and say that it is true — to say that they’re not doing that — is fear-mongering at its worst.”
Cynthia Lambert: 805-781-7929
Upcoming water forum
A water forum will be held April 21 for the public to learn about San Luis Obispo’s water supplies and water shortage plan and get a drought update.
The forum will be held from 6 to 9 p.m. at Ludwick Community Center, 864 Santa Rosa St. in San Luis Obispo.
At 6 p.m. city staff will be available to talk about water-related issues at various booths: conservation, water sources and supply, and upgrades to the city’s wastewater treatment plant.
At 7 p.m., the staff will discuss updates to the 2010 Urban Water Management Plan, including changes to the water shortage contingency plan, followed by a question-and-answer session. The forum will stay open until 9 p.m. for people to visit booths and ask questions.
The city’s water shortage contingency plan will go to the Planning Commission on April 27 and to the San Luis Obispo City Council on June 14.