High in the mountains of Arizona, the state’s water supply is slowly piling up. Across craggy peaks and sprawling ponderosa forests, blankets of winter snow represent the first step in filling Arizona’s reservoirs.
The snow that falls at high elevation will melt into soils, streams and rivers before it's collected in reservoirs that feed kitchen faucets and grassy lawns in the Phoenix area, about 100 miles away. At the source, when the water is still frozen, scientists are hard at work measuring and understanding it.
Zachary Keller, a field hydrologist for the Salt River Project, trudged through shin-deep snow on his way to a measurement station near Happy Jack, a once-bustling logging camp. Now, it’s a tranquil sea of pines and trickling mountain streams.
“I can't believe they pay me to do this,” he said with a smile. “Best job I ever had.”
At more than 7,500 feet above sea level, this spot — about halfway between Payson and Flagstaff — often spends much of the winter under snow. With the sun beating down, the last storm’s deposit was already turning slushy.
“Did you notice all the running water off the side of the interstate or the highways coming up, making its way down the hill?” Keller said. “We were pretty excited to see that. Seeing those flow is a big deal for us, because that means that water is heading on down to us.”
Keller and his colleague, Stephen Flora, unpacked their equipment at the monitoring station.
This site is one in a vast network of stations that gather snow data across the West. The Natural Resources Conservation Service gathers information from more than 1,000 similar stations that span from northern Alaska to southern New Mexico.
An array of high-tech sensors takes readings of the snow conditions here and beams them, in real time, to a database. Keller said it’s still important to double check those numbers by taking additional readings in person.
“Having eyes in the field 24/7 is always great,” he said, “but you can't always trust an instrument. You have to come out and you have to calibrate it. You have to ground truth it. That's something that will never change.”
Keller took a long aluminum tube and plunged it into the snow at his feet, careful not to scoop up too much dirt along with it. With a twist, he pulled it back up and looked at the depth of snow within, reading the findings to Flora, who jotted them down on a notepad.
Even after the introduction of high-tech instruments in the 1970s and '80s, scientists have been taking similar by-hand snow measurements in the Mountain West going back to the 1930s. The equipment has looked basically the same for nearly a century.
Keller and Flora weighed the tube using an analog scale, and did some calculations to figure out exactly how much water was held in the snow.
Those numbers, they said, play a pivotal role in managing major reservoirs in the hills above Phoenix.
“Most of the water that everybody uses down the Valley — our 2.5 million customers — the vast majority of that is generated during spring runoff snowmelt,” Keller said. “So understanding how much water is up here in the snow before it starts to melt is really crucial to us.”
Snow that falls near Happy Jack takes a long, meandering journey through mountain creeks and the Verde River before it arrives in Horseshoe Reservoir and Bartlett Reservoir. From there, it flows to kitchen faucets and irrigation canals in the Phoenix area.
The Salt River Project, which manages those manmade lakes, needs to decide how much water it can release from those reservoirs every summer, and how much it might need to rely on other sources — like groundwater — when they’re not full enough.
This year’s data is subpar. This portion of Arizona is, like much of the Mountain West, facing a dry winter. Snow totals at Happy Jack have been below average since early December, and a heatwave is likely to melt the little snow that arrived in February. Despite the relatively meager snow outlook, Flora said there’s reason for optimism this year.
An unusually wet fall loaded up the area’s soils with moisture, so any new snowmelt is more likely to flow downstream instead of getting soaked up by dry, thirsty dirt.
“This snowpack here,” said Flora, a senior hydrologist for SRP, “Since the soil is already saturated, we're going to expect that to run off. So if we don't get any more storms, our forecasts can go down. If we get a good March and we get some more storms, it can go quite a bit up.”
Flora said climate change makes this water supply highly variable and harder to predict. This time of year last year, there was about half as much snow. In 2023, though, there was about five times as much.
“We might have longer stretches of drought,” he said, “We might have more severe drought, or we're also going to have wetter years, bigger floods and bigger storm winters and seasons that can have a lot of flow across the Salt and Verde watershed.”
Wet winters can ease a lot of summertime anxiety for water managers. Flora said more than 60% of SRP’s water supply arrives in the winter. Storms in the colder months, far away from the Phoenix metropolitan area, have much more impact than the summer monsoons that bring rain closer to home.
“We're all very excited when we get a wet summer, when we get a lot of thunderstorm activity,” said Erinanne Saffell, the Arizona state climatologist. “But really, those wet summers aren't necessarily part of our water supply. What that does is it helps our forests, it helps our vegetation, it helps our ecosystems, when we have a wet summer. It's really that wet winter, getting that snowpack, that helps with our water supply.”
Arizona’s Salt and Verde River watersheds may be getting even more important for the Valley’s water supply. Many cities in the Phoenix area use water from a variety of different sources, and one of those sources is facing major threats.
The Colorado River, which is piped to the Valley through a 336-mile canal across the desert, is in the midst of a megadrought stretching across more than 25 years. The Central Arizona project, which manages that canal, might be forced to take deep cuts under new management plans for the Colorado River.
Those plans aren’t yet formalized, but Brenda Burman, CAP general manager, is already sounding the alarm about their potential impact to Valley water supplies.
“It is a devastating hit to the state of Arizona,” Burman told KJZZ in January. “It appears they are trying to wipe us off the map.”
As the threat of Colorado River cutbacks comes into focus, some cities are preparing to lean harder on their supplies from the Salt River Project. A group of SRP water users is exploring a multibillion-dollar expansion to the dam at Bartlett Reservoir, which would allow them to store more water from the Verde River after extraordinarily wet winters.
EDITOR'S NOTE: This story has been updated to correct the number of SRP customers in metro Phoenix who use water generated in spring runoff snowmelt.
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