Snowpack in the upper Colorado River basin is slightly less than normal for this time of year, meaning Arizona could see sustained water cuts through 2026.
Though trends could change through the rest of the winter, the snowpack in the basin is about 94% of the median for mid-January. While Arizona’s share of Colorado River water in 2025 is already set, the snowpack numbers are early indicators of how much river water the state could get next year.
Even with an average snow year, water managers say dry conditions and warming temperatures could create below-average runoff, keeping Arizona water users in shortage.
Arizona relies on snowmelt for much of its water supply. About 36% of the water used in Arizona’s households, businesses and farms comes from the Colorado River, mostly comprising melted snow from mountainous areas in Colorado, Wyoming and Utah. Arizona’s water managers can watch snow conditions using a network of snowpack measurement sites operated by the U.S. Department of Agriculture.
Nolie Templeton monitors Colorado River supplies for the Central Arizona Project, a 336-mile canal system that brings Colorado River water to areas around Phoenix and Tucson. Templeton said this winter has been abnormally dry for southern areas of the basin like Arizona and New Mexico, but northern areas have received normal precipitation. That snow, falling as far away as Wyoming, will provide Arizona’s water in coming years.
Even with average snowfall, Templeton said, Arizona might not get relief from recent shortages on the river. Projections of how much snowmelt will run down the river this year have declined since early December, reflecting a lack of snow and shifting weather patterns in the Pacific Ocean. Government scientists now project that the basin will see roughly 82% of its normal runoff this year, down from a projection of 90% in December.
“What we’ve seen, based on drying conditions and higher temperatures is that about-average snowpack means below-average runoff,” Templeton said.
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‘We’re planning for less flow in the Colorado River’
Even when the snowpack is strong, other factors can keep that snow from turning into river runoff. Dry soils, human water use and sublimation (a process where snow and water are lost to the atmosphere) can all soak up snowmelt before it flows to Arizona. Templeton said the effects of climate change could be increasing those losses.
In 2024, the basin saw peak snowpack about 5% above the median, but runoff was 17% below the median. While 2023 had huge snow (50% above normal) runoff exceeded its median by a smaller amount (40%).
“We’re learning more every day, but what we’re learning is that when precipitation falls on the watershed, it’s not as efficient as it used to be,” Templeton said. “We’re seeing higher temperatures impacting our hydrological cycle. We’re planning for less flow in the Colorado River. That’s not to say there won’t be periods of high flow here and there.”
That reduced runoff means less water for Arizonans. The water levels in the river’s second largest reservoir, Lake Powell, largely dictate how much water is released to lower basin states like Arizona. Federal dam managers already used existing guidelines in 2024 to determine Arizona’s share of the river for 2025, so the snowmelt flowing into the reservoir this year will define Arizona’s share in 2026.
Based on rough projections available this year, Arizona will likely remain under existing cuts to its Colorado River use. Under the conditions of several interstate agreements, Arizona has operated under a “Tier 1 shortage” on the river since 2022, a result of drought and overuse that have strained the Colorado. Under the cuts, Arizona has given up about 8% of its previous water supply, according to the Arizona Department of Water Resources.
The basin could still get a big influx of snow this winter, Templeton said, a scenario that played out in 2024. Pacific ocean temperatures, which have a strong effect on weather patterns in North America, have shifted toward a brief “La Niña” condition this winter. Templeton said the La Niña pattern has no strong correlation with precipitation in the upper Colorado River basin, so it’s hard to tell whether the river will get a late-winter dump of snow.
“It just takes a couple of really big storm events, and you get above that median. It’s yet to be determined if we get those events in 2025,” Templeton said.
While early projections can be somewhat useful, Templeton said it is still too early to know exactly how the snow year will shake out.
“We’re right around the median,” Templeton said. “However, we have a lot of snowfall season left to go, and we don’t know how it’s going to go.”
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Within Arizona, river basins have received almost no snow. The snow-fed Salt and Verde rivers, which provide about a quarter of the Phoenix area’s water, both stand at less than 10% of normal snowpack for this time of year.
“You can’t really get much drier than dry,” said Bo Svoma, a climate scientist and meteorologist at the Salt River Project. “On paper, this winter is about as dry as it can get.”
Svoma said this is probably one of the basins’ driest early winters in 100 years, though the historical data isn’t good enough to confirm that.
SRP, a reservoir and canal network that delivers Salt and Verde water to users in the Phoenix area, will rely on groundwater and existing supplies in its reservoirs to make it through the dry year, Svoma said. SRP reservoirs were about 70% full as of Jan. 14.
Svoma said water users probably won’t see the effects of this dry year anytime soon. Reservoirs would have to drop to 30% of capacity before managers get concerned and start implementing water cuts. It would take two more hot, dry summers and another bone-dry winter before reservoirs could drop that low, Svoma said.
SRP reduced water deliveries in 2003 and 2004 after a sustained drought drew reservoirs to precariously low levels.
The basins could see a big surge of snow later in the winter, but that hasn’t happened in recent years. Without massive precipitation, desiccated soils will soak up whatever moisture Arizona does receive for the rest of year, Svoma said.
“We’re really facing an uphill battle right now for getting a good runoff season into the reservoirs,” Svoma said.
Austin Corona covers environmental issues for The Arizona Republic and azcentral. Send tips or questions to austin.corona@arizonarepublic.com
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This article originally appeared on Arizona Republic: Early snowpack in Colorado basin is average, cuts likely to remain