It certainly helps, but it isn’t a guarantee. That is because the relationship between the amount of snow and amount of streamflow is highly variable. We tend to think that the snow falls and then just sort of sits there and waits until spring, but it doesn't. Snow evaporates or sublimates over the course of the winter, so we lose a fraction of water to the atmosphere. How much we lose depends on things like aspect and elevation, but also year-to-year variability in winter and spring weather. One thing that surprises many people is that when winters are warmer and snow starts melting earlier, we often see greater evaporation, which reduces streamflow.

Once snow starts melting, very little of it runs off directly to the stream—almost all of it goes into the ground.

Historically, we thought only a small volume of melt went into soils, and once those shallow soils were saturated, the remaining melt water quickly ran off the surface and into streams. That’s an assumption that many water management prediction models still rely on. We now know that the ground can hold much more water, which means a large fraction of snowmelt goes into the subsurface and from there takes months or years to get to the stream. That’s a fundamental change in how we think about water resources and an area that my group works on—how much water goes into the ground and, ultimately, to surface streams? How long does it take to get there?

That was even surprising to us! Hot, sunny days increase melt, and we see the stream respond quickly, so it seems like it may take only hours or days for snowmelt to get to the stream. While that may be true for a fraction of melt, we now know that the average age of all the water molecules during snowmelt can range from a few years to 10 years old.

It’s only been in the last handful of years that we’ve had the tools to accurately date mountain waters. One of my colleagues here at the U, Kip Solomon, is one of the preeminent authorities in the world in determining the age of groundwater. Even he was surprised at the ages of some of these waters during snow melt.

Yes! That is a big part of why the lake didn’t increase more. Last year, many people were concerned there would be huge flooding like in the 1980s, the last time we had that big of a snowpack. But unlike in the 1980s, groundwater storage was at near-record low levels. The amount of groundwater storage is one of the primary controls on how efficient snow melt is for generating stream flow. In other words, a large fraction of snowmelt recharged groundwater rather than contributing to flooding. Surface water resources also were at very low levels, so much of the streamflow filled those stores instead of reaching the Great Salt Lake.

Over the last several years, my now former graduate students Andrew Gelderloos, Logan Jamison and Meg Wolf documented how mountain groundwater responds to multiple years of snowfall and temperature. The last 20 years have, on average, been dry and warm, resulting in very low levels of mountain groundwater. Because snowmelt fills groundwater first, snowmelt runoff has been lower than what we would otherwise expect. In 2022, when Utah had close to average snowpack levels, we saw lower-than-expected spring streamflow. It takes several years to refill groundwater storage, so levels were still low in 2023. Consequently, we saw a good stream flow, but we didn’t see record breaking stream flow and floods.

I like to describe it as a similar system to a hydraulic brake system in your car or bike. You know how you can stop your car by applying just a little pressure to the brake pedal? That small amount of pressure goes into what’s called a booster cylinder. In the old days, they had very large booster cylinders underneath your hood. You’d put a relatively small amount of pressure on that big area, which would be translated through small tubes to your brakes, and that multiplied the force to stop the car.

When snow melts everywhere, there's just a small amount of force of water all over the mountain watersheds. It pushes down through the soil, down through the bedrock, down through all these groundwater stores until it finally pushes out the water already in ground storage through very narrow areas along/into a stream.

The work from many different people, including here at the U, is demonstrating that the flows that we have in streams, and the water that we have in the Great Salt Lake, is a function of climate over multiple years interacting with groundwater. Again, it is a fundamental shift in the way we think about water resources. We used to think surface water and groundwater were separate things. Now, we know unequivocally that they're really the same water resource.

The three best predictors for the amount of water that could get to Great Salt Lake are the amount of precipitation, groundwater levels, and how fast the snow melts. Several years of average or above-average snowfall, which is what we have now, tends to recharge the groundwater. When the groundwater levels are higher, it's more efficient at getting water into the streams and rivers and reservoirs. What I mean by efficient is, how much of the total snowfall is reflected in the volume of stream water flows? The more efficient water is in getting into the streams and rivers and reservoirs, the better we can manage it and make decisions about where the water goes.

In the last few years, our mountain groundwater store has increased from near-record lows to close to average. Surface reservoir levels are now close to full. Both of those facts will make it easier to get water to the lake. In the longer term, we will see drought again, and when we're in times of drought, it's hard to get water to the Great Salt Lake. Difficult decisions will need to be made, but we can do it.

Our work on understanding the connections between climate, snow, groundwater, and surface water is just one part of many ongoing efforts to help improve water management. Current water management policies were developed when the focus was to get water to users, not to get water to the Great Salt Lake. Increasing populations and a rapidly changing climate require coordinated efforts from many disciplines to ensure sustainable water resources for the future. Because water is involved in almost every aspect of society, the challenges are complex and interrelated. There are many people working in universities, state, and federal agencies to help Utah put flexibility in the system to get more water to the lake. For example, colleagues in atmospheric sciences are working to provide better predictions of snowfall and temperature. Researchers in geography are focused on how dust and climate influence snowpacks. Faculty in the College of Engineering are designing ways to treat and reuse water. Biologists across campus are learning more about the water needs and limits of ecosystems, while colleagues in the College of Law are directly helping to develop new, equitable policies. That is just a subset— there are nearly 200 faculty on campus with research and interests on various aspects of water. All of these areas will be needed to help inform better water policy. The good news is that the U’s Peak Water Engine is beginning to coordinate campus efforts with related efforts led by the state and other universities.