October 1 marks the start of Water Year 2026.
Hydrologists and water experts use October as the start of the water year, especially in the Western United States, when the majority of precipitation shifts from rain to mountain snow, and snowpack begins accumulating.
"Flows on rivers are typically near their lowest of the year by the time you get to the beginning of the water year," said Seth Arens, a research scientist with the Western Water Assessment.
Arens, who is based at the University of Utah in Salt Lake City, said that the upcoming water year will be a crucial one for the West, both in terms of the climate, and politically, as water negotiators from the seven Colorado River Basin states attempt to work out new operating guidelines for the river.
"What I would say is, we haven't been forced to adapt quite yet, is the short answer," he said. "But those things are coming to a head extremely rapidly."
Water Year 2025 saw inefficient runoff, drought conditions
Water Years 2023 and 2024 were both wet years—with 2023 breaking records in the Lower Basin states of California and Nevada. But Water Year 2025 was drier than average for the Upper Colorado River Basin.
Overall, Arens said, the Upper Colorado River Basin, or the areas above Lake Powell, on average had about 86% of normal snowpack, which is somewhat drier than usual, but not catastrophic. The basin had issues with inefficient runoff, which means that only part of the water in the snowpack makes it into rivers and streams. Arens said that between April and July, which makes up the main runoff season, the basin saw 41% of average streamflows.
Arens said that inefficient runoff also had a negative impact on water forecasters and the information they were able to provide to water managers in the Upper Basin.
"In January, the stream flow forecast from the Colorado Basin River Forecast Center was 81%," he said. "By the time we got to April, that had decreased to 67%."
Arens said that date is important, because most of the melting and runoff takes place from April to July.
"This April 1st water supply forecast is often the number that water managers are thinking about," Arens said. "It's like, 'okay, we've gotten all the snow we're gonna get, we have a good idea of what's in the mountains.' And that forecast is often pretty accurate, and that's what water managers will start planning their season based on."
But this year, the predictions were way off. Arens said that by the time runoff was over, the basin only saw 41% of average streamflows.
"This has to do with some of the impacts we're seeing from climate change, that the system is just working a little differently than it had historically," Arens said.
Later in March, there was a spring heat wave that caused a lot of very rapid snowmelt, followed by a cooler period in April.
"Having these early periods of warmth in the late winter, and then a colder spell, you lose some of the water to the system," Arens said.
He said that's just one indicator of climate change. Other impacts are evident in trends seen throughout the basin, especially in dry years.
"Drying soils, melting snow sooner, maybe less of that precipitation is falling as snow, especially at low elevations," he listed. "You're getting low elevations to melt out sooner. Things like that."
But Arens said it's important to distinguish between different parts of the Upper Basin.
For instance, in the northern part of the basin, snowpack and snow-water equivalent, or SWE—the amount of water that's stored in the snowpack—was close to normal. The Yampa and White rivers, as well as the Upper Green and the headwaters of the Colorado in Grand County, all saw near average snowpack and SWE.
But in the southern part of the Upper Basin, especially southwestern Colorado and the Four Corners region, some rivers got to historically low points. The Gunnison was at 36% of average SWE in May, and the Upper San Juan was at just 31%.
"This (area) is really kind of the bullseye of the millennial millennium megadrought that we're largely still in," Arens said.
Water Year 2026 will start with dry soils
Much of the Upper Colorado River Basin will be entering Water Year 2026 in some state of drought. On October 1, 2024, only 7% of the Upper Colorado River Basin was experiencing drought conditions. As of Monday, September 29, 2025, all of the basin was in a state of drought, with over 80% of the region in severe to extreme drought.
Arens said it can be difficult to determine if the Upper Colorado River Basin will have a wet or dry water year, because seasonal forecasts aren't always accurate. But Arens said at the moment, the National Oceanic and Atmospheric Administration (NOAA) is predicting what he calls "a classic La Niña setup." That means a higher probability of above-average precipitation in northern states like Washington, Oregon, and Montana, and below average precipitation in Arizona, New Mexico and parts of Utah and Colorado.
"At least for the very first part of winter, the probability is trending towards below average precipitation for probably the southern two thirds of the Upper Colorado River Basin," he said.
There are other factors, Arens said, that can help forecasters understand what might be on the horizon for the upcoming water year. One factor they're observing now is how dry soils are throughout the region.
"When you have dry soils, that is indicative that there's almost certainly going to be an inefficient runoff," he said. "So that means if the soils are really dry, the first part of that melt period, all the water is going to go into just rewetting those soils."
Arens said October precipitation can have a big impact on soil moisture, and could improve the outlook.
"Really any good precipitation we have is going to increase soil moisture," he said. "And at this point, that's a good thing if we get the soils wetter before we start to get snow on the ground."
Arens and his colleagues will also closely monitor Lake Powell and Lake Mead, along with other major reservoirs in the upper basin, like Flaming Gorge on the Utah-Wyoming border and Blue Mesa near Gunnison.
"Lake Mead is 31% full and Lake Powell is 29% full," Arens said.
In terms of storage capacity, he said those numbers aren't quite as bad as they were after a very dry 2022 water year.
"But we're close and if we have another drought winter, then things are almost certainly going to be just as bad as they were in 2023, if not worse," he said. "In fact, the worst case projections by the Bureau of Reclamation on water elevation…has Lake Powell falling to the level of below minimum power generation in Glen Canyon Dam by fall of next year."
Copyright 2025 Rocky Mountain Community Radio.
This story was shared via Rocky Mountain Community Radio, a network of public media stations in Colorado, Wyoming, Utah, and New Mexico, including KSUT.
