Is Arizona’s water supply getting boost from recent storms, El Niño?

Recent storms in Arizona may have helped raise some reservoir levels, but snowpack is more important to the state’s water supply than rain, according to a local expert.

“Rain is not what our reservoir systems are designed to capture. So, rain helps, and it helps directly and indirectly, but it’s not what we need,” Sarah Porter, director of the Kyl Center for Water Policy at Arizona State University, told KTAR News 92.3 FM’s Arizona’s Morning News on Wednesday.

Porter explained that the Phoenix-area water system managed by Salt River Project (SRP) relies mostly on snowpack from the mountains in national parks east and north of the Valley.

“And then we have the Colorado River system, and that’s a system that’s really stressed,” she said. “And that system relies on snow, not rain, but snow in the upper Rockies, up in Wyoming, in Colorado, Utah.”

While rain does not directly make a significant impact on the Colorado River system, it does have an indirect benefit, Porter said.

“The other thing that rain does that really helps is it makes the ground wet,” she said. “And that means that in those places where we rely on snowpack to melt slowly and turn into flows in rivers, the ground isn’t going to sponge up as much water, hopefully.”

Will El Niño help or hurt Arizona’s water supply?

It is difficult to predict how much this year’s El Niño weather pattern, which typically increases moisture in the Southwestern U.S., will help Arizona’s water supply.

Porter said rainfall helps fill SRP reservoirs, which she called “pretty resilient.”

“Unfortunately, El Niño does not have the same impact in the upper Rockies. It’s about even chances up there,” she said.

Studies about how El Niño can be expected to affect snowpack in the mountains that feed the Colorado River system are mixed, with some saying it has little or no impact and others saying it actually reduces snowfall.

“There’s no reason not to hope that we would have snow in the upper Rockies, but we certainly shouldn’t count on it for our water management strategy,” Porter said.

Regardless of what happens in the Rockies during the fall and winter, Arizona will see its Colorado River water allotment reduced next year under a new operating agreement. Although Upper Basin states did not have to take Colorado River cuts, they are experiencing significant water supply issues, Porter said.

“Regardless of how we feel about our neighbors in those upper Rocky states, they have had a terrible year,” she said.

Lake Mead and Lake Powell, the two largest reservoirs in the Colorado River system, reached all-time low levels this summer.

Porter said farmers in the Upper Basin states rely on rivers and streams that are running dry, forcing them to cut back on planting.

“They have big water restrictions in Denver. They are experiencing the impacts of this drought in a real, real way,” she said.

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