Explosive Population Growth Will Pose Challenges to Phoenix Metro Water Future

Editor’s Note: This is the first in a five-part series called “KTAR Water Watch”, which will explore the present and future of water supply across Arizona and the metro area. of Phoenix.

PHOENIX – The images are shocking. Areas submerged for decades are now islands.

Lake Mead and Lake Powell, two reservoirs that Arizona depends on for water, are historically low, each about a third full.

Arizona State University climatologist Randy Cerveny said that in addition to climate change, it’s the explosive population growth in Arizona and other states that depend on water from the river. Colorado via Lake Mead and Lake Powell which will present future challenges in the valley.

Cerveny says most of the water that fills the Colorado River is due to melting snowpack in Colorado. The state is going through a historically dry period, and the Rockies have not seen consistent, above-normal rainfall.

“The river is so tightly allocated that just south of Yuma, every remaining drop is sent to California,” Cerveny said. “It no longer reaches the Gulf of California. Even if there were to be more additional water falling over the Colorado Rockies and into the Colorado River, it has already been allocated.

“We will never see these lakes return to the pre-drought times we are in now.”

The valley gets about 30% of its water from the Colorado River through the Central Arizona Project Channel.

The Salt River Project supplies about half of the Phoenix metro area’s water—about 2.5 million customers—from its chain of reservoirs on the Salt River and Verde River. The rest of the valley’s water supply comes from groundwater.

The region’s continued population and commercial growth could strain the entire system, but Cerveny says not all water sources will dry up at once.

But is the company’s growth sustainable given the resources available?

“It will depend on what community they will be affiliated with, as different organizations will need to use different water sources,” Cerveny said. “SRP is quite picky about who they allow access to their water. There are other sources that charge a lot for their particular water.

Storage in SRP reservoirs has declined very little since 1996, thanks in part to some recent wet winters in 2017, 2019 and 2020.

The winters of 2005 and 2010 were also strong, while last summer’s powerful monsoon also added water to the system.

SRP’s chain of six reservoirs on the Salt River and Verde River provide about half of the valley’s water supply, and collectively their capacity is about 70 percent.

The Central Arizona project has seen the first and so far only water cuts due to declining reservoir levels, but the reduction is only impacting agriculture so far.

SRP scientist and meteorologist Bo Svoma says flows from the Colorado River basin to Lake Powell are highly sensitive to warming, while the Salt and Verde rivers are about five times less sensitive to warming.

“What warming does is it increases evaporation losses from the landscape and drives less water for stream flow,” Svoma said. “The Colorado River is more sensitive to this than the Salt and the Verde.

“That’s one of the reasons things aren’t as dire on the Salt and Verde.”

Even with the Valley’s explosive population growth since the mid-1990s, Svoma says demand has actually declined.

“SRP has delivered less water due to better water efficiency and use and people are more conservation conscious with their water use which is really important,” said said Svoma.

“This brings the SRP into perfect balance with the long-term median inflow into the system equaling our water deliveries, which is not the case on the Colorado River, which is over-allocated.”

Svoma does not see Lakes Mead and Powell dropping to the point that they can no longer supply water to the valley.

“I think it’s going to be tough to fix the over-allocation on the Colorado River, but people are working on it,” Svoma said.

“What will happen with future precipitation is highly uncertain, but from a western U.S. perspective, climate model projections are leaning toward increased winter precipitation for the Colorado River, which is positive.”

Will the water situation impact the ability to attract business, especially semiconductor companies? Svoma says yes.

“Water supply certainty is attractive to business, and several projects underway could increase the resilience and sustainability of Arizona’s water supply,” Svoma said.

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