What if it's too warm to snow? Water managers across the West need to adapt, report says

Arizona and the West could see their water supplies drop by as much as 30% by the middle of the century as warmer temperatures lead to less snowfall, reducing runoff into rivers and reservoirs, changing vegetation cover and altering wildlife habitat.

Those are the findings of a team of researchers led by Erica R. Siirila-Woodburn and Alan M. Rhoades at the Lawrence Berkeley National Laboratory, who published a paper looking at the likelihood of a "low-to-no snow" future. Their analysis, published in the journal Nature Reviews Earth and Environment, also estimates when and where to expect the effects of a low-to-no snow climate disaster.

The researchers reviewed over 260 papers on snowpack in the region. Their review paints a grim picture of snow's future and water use in the region, as the Western U.S. is heavily reliant on spring snowmelt for water, with up to 75% of water resources coming from snowmelt in some states.

Based on their modeled simulations, the researchers concluded that 8-14% of winters between 1950 and 2000 could be categorized as a low-to-no snow season. Using the same model, they projected that the number of snow-free winters is expected to increase to 78-94% from 2050 to 2099.

As a result, the researchers say water managers will find it harder to meet the water needs of millions of people, especially if they use historical allocations as benchmarks to plan for the future.

The findings arrive in the middle of an unusually warm fall in the West, where temperatures have remained high and precipitation in any form has been scarce. Flagstaff is already about 8 inches behind the average snowfall by Dec. 1.

The goal of the research was to compile information from various papers into a single assessment so policymakers and water managers could have qualitative data regarding when a low- to no-snow future might occur, how it might affect water use and what potential strategies they could use to cope with a warmer, drier climate.

"The motivation was to, in part, bring more awareness to snowpack disappearance in the Western U.S., but also to draw some synthesis around what kind of magnitudes of snowpack loss could be expected in the coming decades," said Siirila-Woodburn, one of the lead authors of the paper. "And then also draw some of the connections between the implications for some of that snow loss, specifically focused around water resources."

Snowmelt produces significantly more useable water than rain, which is prone to evaporation and runoff. In the West, a significant portion of the water infrastructure is built around spring snowmelt. The scale of snowpack reduction, which in the paper is assessed using Snow Water Equivalent, is difficult to gauge. Snow water equivalent is essentially the amount of water melted snow produces.

Snowmelt and water are one and the same at different stages of the water’s life cycle. Before water runs off into reservoirs that supply cities, it’s stored in the mountains in the form of snowpack.

In the study, low snow is when the peak snow-water equivalent falls between the 10th and 30th percentiles and no snow is when conditions are within the lowest 10%, the study said. While they admit that chances of zero snow are low, at least in the next century, the researchers said the West is fast approaching a situation where dwindling snowpack will start to have a detrimental impact to water users.

By 2040, parts of southern California are expected to have at least five consecutive years with less than 50% of the anticipated, or average, snowpack. After 2070, throughout the West, more than 80% of winters are expected to be lower than historical averages in terms of snowfall.

"A lot of the results are pretty consistent with other results that have been done by other authors doing similar kinds of work," said Paul Miller, a service coordination hydrologist at the National Oceanic and Atmospheric Administration's Colorado Basin River Forecast Center.

"Snow levels have just been consistently below average since 2000. And when you get those consistently dry years, one, we have less snowpack, which obviously means less snowmelt and less runoff into the reservoirs," Miller said. "But it also means that we get very dry soils in the area, and that leads to less efficient runoff."

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What this means for Arizona

Given Arizona’s warmer climate and lower elevations where snow falls, a lot of precipitation already falls as rain in winter. Even in some of the higher elevations, where snow is likely to occur, the winter season is shorter in duration than it is further north in the Rocky Mountains, which means runoff occurs earlier. Evapotranspiration, where water is sucked into the atmosphere or taken in by plants, is also more significant in Arizona because of the shorter winter.

“The big difference of the snow dynamics in the Southwest is the vast majority of the snow sublimates,” said Abe Springer, a professor at Northern Arizona University’s School of Earth and Sustainability. “In fact, it's more than 70% of our snowpack that falls, just evaporates and goes straight back to the atmosphere.”

The differences in timing, elevation and precipitation that make Arizona unique mean the conditions predicted in the study are likely already present in Arizona, said Connie Woodhouse, regents professor at the University of Arizona's School of Geography, Development and Environment.

"Because it's warmer anyway, we already have a shorter snow accumulation season, we already have an earlier melt-off, we already have an earlier peak," Woodhouse said. "Not to say that these won't change but I'm saying we already have those conditions, so (water managers in Arizona) already have these low- to no-snow scenarios that occur naturally. And so they probably have a better handle for maybe what to expect."

A case in point is Salt River Project, which draws from the Salt and Verde river watersheds. Because snowmelt occurs more throughout the winter, at lower, warmer elevations, SRP isn’t as reliant on a single-season event, like spring snowmelt.

Its demand is also about equal to the supply, said Andrew Volkmer, a hydrologist with SRP. Consequently, SRP's reservoirs aren’t as depleted as those in other areas and they’re more resilient to any sort of fluctuations in snowfall.

Meanwhile, water levels in the country’s two largest reservoirs, Lake Mead and Lake Powell, have been plummeting to historic lows for several months. The snowmelt that feeds into these reservoirs comes from the Rocky Mountains by way of the Colorado River. In addition to persistent overallocation, the drop is in some part due to dry winters with less snowmelt in the spring, said Miller, the hydrologist.

The Bureau of Reclamation, the agency that manages the reservoirs, expects water levels to continue dropping all the way through to spring, causing the agency to declare a water shortage, which is expected to lead to water cuts across Arizona, Nevada and Mexico.

The agency that manages the Central Arizona Project, which delivers Colorado River water to Phoenix and Tucson, will be forced to reduce its water allocation by as much as a third. Most of the cuts will affect major agriculture operations.

This winter's La Niña conditions don't inspire much confidence for increased levels of precipitation. The National Weather Service projects a 90% chance that this winter will be drier than on average in Arizona and other parts of the West.

That trend is already evident. According to the National Weather Service, the Flagstaff area typically receives at least 9 inches of snow by Dec. 1. So far, the total is less than an inch. Temperatures, too, have been above average: Flagstaff was 6 degrees warmer than past Novembers and, in Phoenix, temperatures were at least 13 degrees above average.

Winter sports, which is directly dependent on snow and snowpack, is particularly sensitive when snow fails to show. This year, Snowbowl, the state's most northerly winter recreation resort near Flagstaff, has delayed its opening by almost two weeks due to warmer weather and no snow.

Snowbowl resorted to machine-made snow to help keep its delayed opening day promise. Robert Linde, the resort's manager, said Snowbowl is 100% reliant on snow machines for now, though that doesn't have him too worried.

"What you find in Arizona, in particular, in the southwest, is great fluctuations in snowfall. And it's been that way, for a long, long time. I refer to it as feast or famine," Linde said. "There have been plenty of winters I'd say over the last 40 years where Arizona Snowbowl didn't open for Thanksgiving, or didn't open for Christmas, or didn't open at all."

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Adapting to changing conditions

With temperatures expected to continue climbing, the effects of snow scarcity will force municipalities and users to adapt to reduced snowmelt and shrinking sources of groundwater. But that doesn't mean the region is doomed, the report's authors say. They offer several suggestions for water managers who want to mitigate the adverse effects of less snowpack.

Key among their ideas is robust infrastructure, including dams and canals. Other solutions, like management approaches, could also help. Better forecasting, aquifer recharging and conservation could all serve as critical tools to soften the blow to water users.

One of the techniques championed by the researchers is forecast informed reservoir operations, a strategy that uses enhanced monitoring and better forecasting to help managers make decisions about when to retain or release water in reservoirs.

Burgeoning research into that technology is starting to show promise. In northern California on Lake Mendocino, researchers found that such steps could potentially increase water storage by 33%. And in the Feather River Basin, on California's Yuba River, water managers are considering a second, smaller floodgate to buffer New Bullards Bar Dam. The second dam will help make forecasting more precise, said Rhoades.

Another potential strategy, Siirila-Woodburn said, is managed aquifer recharge, where runoff that would go into the ocean is captured and stored in infiltration ponds. That runoff could then be diverted to fallow agricultural fields, which could serve as aquifers for later use.

Above all, the authors hope this report will be a call to action for water agencies and policymakers who will shape how water is used in the future.

"One of the overarching points of this whole paper is to really elevate the urgency of snow loss to the level of other kinds of climate change impacts that you often hear in the news like sea-level rise, or wildfires or changes in weather extremes," said Rhoades.

"This low to no-snow future is not necessarily set in stone," Rhoades said. "There is ample time still to mitigate carbon emissions to the point where this low-to-no snow future in some of these studies that we point out might not actually come to fruition."

Lindsey Botts is an environmental reporter for The Arizona Republic/azcentral. Follow his reporting on Twitter at @lkbotts and Lkbotts on Instagram. Tell him about stories at lindsey.botts@azcentral.com.

Environmental coverage on azcentral.com and in The Arizona Republic is supported by a grant from the Nina Mason Pulliam Charitable Trust. Follow The Republic environmental reporting team at environment.azcentral.com and @azcenvironment on Facebook, Twitter and Instagram.