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What Climate Change Means for San Diego’s Water

Climate change will lead to hotter, drier weather in San Diego, but also more frequent floods caused by larger storms. Water supply will be diminished but demand is expected to increase.

Written by Padma Nagappan Published on Read time Approx. 6 minutes
Anthony Novom waters down smoldering vegetation surrounding his home in the Rancho Santa Fe neighborhood during a wildfire May 13, 2014, in San Diego. Wildfires pushed by gusty winds chewed through canyons parched by California's drought. Climate change will likely mean hotter, drier weather for the San Diego region.Associated Press

SAN DIEGO – San Diego imports 80 percent of its water, with the Colorado River supplying about 63 percent, and 20 percent coming from Sierra Nevada runoff funneled from northern California via the State Water Project. The remaining 17 percent comes from local sources – a mix of rainwater, groundwater, desalination and recycled water.

While these numbers vary from year to year, what hasn’t changed is the fact that San Diego has relied heavily on imported water for many decades. With climate change heralding warmer weather and prolonged droughts, this impacts the level of snowpack and river flow, which in turn threatens the region’s water security.

The San Diego Foundation, which works with the city, educators, community leaders and research institutions on forecasts and planning, commissioned a study of climate impacts and the region’s water resilience.

The report, put together by climate scientists from the Scripps Institution of Oceanography (SIO) at the University of California, San Diego, found that San Diegans need to be prepared for contradictory conditions.

Contrary Climate, Extreme Weather Events

By 2035, demand for water is expected to increase by 46 percent, as the popular sunny region attracts a burgeoning population, while at the same time hotter, drier weather and less rainfall will lead to more soil and reservoir evaporation.

The city’s population is currently at 1.54 million people, and the county at 3.54 million people. By 2050, the city is expected to grow to 1.95 million people and the county to 4.38 million people.

The region will have 16 percent fewer rainy days, but 8 percent more rain during large, intense storms, which could lead to more frequent flooding, according to the San Diego Foundation’s report. The report also predicts a 12 percent reduction in the runoff and streamflow that replenish the area’s major water sources.

In other words, droughts and floods are equally likely – while water supply diminishes and water demand shoots up.

“Our reports tap the latest science to best understand how climate change will impact our region, in terms of water, precipitation and wildfires,” said Emily Young, vice-president of community impact at the San Diego Foundation. “We found the major impact is on water supply.”

Conserve, Recycle, Rethink

During a previous drought in the 1990s – when San Diego used to rely on a single source, the Metropolitan Water District of Southern California, for 95 percent of its water – there were major water supply reductions.

Since then, the San Diego County Water Authority (SDCWA) has diversified its water supply, boosting storage at the San Vicente Dam, increasing capacity at water treatment plants and securing a supply agreement with the Imperial Valley’s irrigation district to transfer water.

An expensive seawater desalination project also began functioning in December 2015, after years of delays. This will supplement the region’s water supply by about 7–10 percent while it raises the bills of water customers.

But in addition to all this, given the arid climate forecast, the region needs to squeeze water from every possible source to make up for fast-depleting water resources.

“Many cities in San Diego County and across California are looking at how to rethink their infrastructure,” Young said. “They’re looking at pipes that can capture stormwater, and do more rain collection on site. The San Diego airport has more stormwater runoff than it can use in a year, so they’re looking at how to reuse this water.”

Dan Cayan, a climate scientist at SIO and one of the report’s authors, explained, “Using water wisely, conserving and recycling are really critical because of the factors that will come into play that will challenge us – greater water demand, bigger droughts, warmer conditions, precipitation regime changing to a more volatile climate where it comes in bursts.”

He cautioned that while the SDCWA has done a good job in expanding the water supply portfolio, the region still depends on imported water, which is expensive both monetarily and in terms of the energy required to transport and purify it.

“When we compare Southern California to other Mediterranean regions, we are up there in terms of extravagance,” Cayan pointed out. “In the past few years, we’ve been able to conserve quite a bit and that’s a testimony that we’re able to economize.”

The region’s water consumption decreased by 24 percent at the end of 2015, beating the 20 percent savings target set by Governor Brown’s state-mandated emergency water savings goal.

“My mantra is: Conservation is a good thing and in the long run we will have to conserve more as a society,” Cayan said.

Severe Storms and Sea Level Rise

The Carlsbad, Calif., desalination plant provides water to San Diego, but the majority of the region's water is still imported from the Colorado River or the Sierra Nevada. (Lenny Ignelzi, AP)

The Carlsbad, Calif., desalination plant provides water to San Diego, but the majority of the region’s water is still imported from the Colorado River or the Sierra Nevada. (Lenny Ignelzi, AP)

At the other end of the spectrum is flooding – also a very real possibility.

The much-anticipated El Nino was not as severe as the region had geared itself up for this year, but it did bring copious amounts of rain over several days, which led to flooding in some areas, including the low-lying Tijuana River Valley.

Young recounted how 6 billion gallons (22.7 billion liters) of water flowed down the river valley and into the ocean, flooding neighboring streets, backing up storm drains and leading to a fish die-off.

Flooding can happen due to sea level rise (oceanic flooding) and from severe storms and increased precipitation (atmospheric flooding).

Atmospheric flooding happens when hotter weather leads to increased evaporation from the ocean’s surface.

“If you walk into a bathroom where someone took a hot shower, the room is warmer and as it cools, there’s going to be more condensation,” Cayan explained, comparing this with how a warming planet sends more water vapor into the atmosphere, leading to an atmospheric river as it’s called, of which one type is a “pineapple express.”

The terms refer to a fast-flowing stream of water vapor-laden airmass that makes its way on to the West Coast, which – when combined with sufficient storm dynamics – forces the air to rise over mountain ranges, leading to abundant rain or snow. This is often accompanied by flooding, mudslides, downed trees and travel delays.

“Even though San Diego is sheltered by a high pressure system called the North Pacific High, occasional storms do transport moist air that can bring very intense precipitation,” Cayan said.

In San Diego, concentrated rainfall spread over fewer days will lead to flash floods, so much so that once-in-100 years type of floods could occur once a year by 2050, and speed up to once a month by 2080 in some parts of the region, Young said.

“The challenge with climate change is the combination of these factors that play out in seemingly contradictory ways,” Young said.

As the oceans warm up, the volume of water increases due to thermal expansion, which leads to sea level rise and potential oceanic flooding. Over the last 100 years, sea levels have risen by 6–8in (15–20cm) on average around the globe, but since the year 2000, the rise has accelerated to 0.08in (2mm) a year.

Cayan explained that this is caused by two factors – warming oceans and melting of glaciers and ice sheets in Greenland and Antarctica. “It’s kind of like a rising bath tub. El Nino will increase sea levels along with high winds and more erosion, just like when we lost lots of vulnerable coastal structures back in the 1982–83 El Nino.”

How the Region Will Cope

San Diego’s community response planning has matured over the last few years, he observed, which has helped. Its energy supply will shift to cleaner energy sources as part of its climate action plan, and as it conserves more water, it will use less energy to transport and filter it.

“We just need to get more climate smart, and do a better job of tracking how much energy and water we use,” Cayan said.

Chula Vista, a city near the Mexican border that’s a leader in sustainability initiatives, is one of the first in the country to have a comprehensive climate adaptation plan. “They show how smaller cities can be models for being more entrepreneurial,” Young highlighted.

The San Diego region takes pride in being collaborative, and this spirit of collaboration extends from its thriving biotech research sector to innovations and planning across the board.

“We can build on this to go to the next level, and by investing today, we can ensure we adapt to climate change so future generations enjoy the quality of life we’ve come to benefit from ourselves,” Young said.

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