When water managers in Arizona are trying to plan for how much water they’ll get from rivers and reservoirs, they look to the mountain snow. A new study compares different programs for measuring that snow, and found that they produce wildly different estimates.
The study, published in the journal Water Resources Research, mostly found problems with long-term models, and said most water managers in the Southwest are using more accurate systems for predicting the amount of water in reservoirs in the near term.
High-altitude snow is far more important to the Southwest’s water supply than summer rains, so getting accurate data about that snow is pivotal for the people who make plans for the water that flows to cities and farms across the region. At a time when the Colorado River is stretched thin, measuring water supplies down to the drop can make a big difference for the tens of millions of people who depend on it.
The study highlights a University of Arizona program as one of the best snow measurement tools.
Jessica Lundquist, a professor of civil and environmental engineering at the University of Washington who authored the study, said different programs produced a wide range of estimates for the amount of water held in snow across the West — ranging from “less than the amount of water in Lake Mead” to “five Lake Meads.”
Lundquist and her team identified three main problems with inaccurate modeling programs. First, some large scale models run at a global scale and are not very high resolution, so they don’t accurately map the way that snow is nestled in complex, craggy mountain ranges. Some programs produced misleading estimates about the depth of snow, and some overestimated how quickly snow was melting.
The best snow models, Lundquist said, combined remotely gathered data — like information from satellites — with real-world observations from the ground, like physical sensors that measure the weight of snow using a kind of scale on the ground.
“It's a wake-up call of how important our observational networks are,” she said. In times when we're thinking about — ‘It costs a lot to repair things,’ ‘Do we need these?’ Those were really important factors in the models that got snow right.”
Lundquist, whose study looked at different river basins around the Western U.S., said snow measurements for the Colorado River were some of the most accurate because water shortages have driven a need for more precise data.
“I was impressed at how much recent progress there has been on really quantifying the amount of snow in the Colorado,” she said. “A lot of the available products right now did a lot better than I expected going into the study. So I would say that for the Colorado in particular, recent investments in measurements and science have been paying off.
