In the mountain ranges of Western North America, winters are not what they used to be. More rain is falling instead of snow, and the snow is melting earlier. The resulting leaner snowpack could pose significant problems for agriculture, wildfire risk, and municipal water supplies come summer, according to a study conducted by the University of Colorado Boulder.
The study, published in Nature Communications Earth & Environment, chronicles over six decades of change in snowpack water storage across this region.
From 1950 to 2013, there has been a significant reduction in snowpack water storage in more than 25 percent of the Mountain West. This is partly due to snow melting earlier in the winter and spring seasons, effectively wearing down this seasonal boundary.
“On average and in every mountainous region that we looked at, snow melt is occurring closer in time to when it fell,” explained study lead author Kate Hale.
This shift in the timing of water availability is moving toward earlier in the springtime, with less snow melt and water availability later in the summertime, implying an impending water scarcity later in the year.
Western U.S. and Canada heavily depend on snow for most of their water needs. For a long time, the Rocky Mountains, Sierra Nevadas, and other mountain ranges have been the region’s “water towers,” storing snow throughout the winter which then melts and provides water in the spring and summer when demand is highest.
Every April 1st, state and regional water managers use a metric known as the snow water equivalent (SWE) to predict and plan for water resources that year. But this measurement is merely a snapshot and does not reveal how the snow accumulated or if it is already melting, says Hale, who is currently a postdoctoral researcher at the University of Vermont.
“From a hydrologic perspective, the only thing that’s unique about snow is that it delays the timing of water input to watersheds. And just looking at a snapshot of snow water equivalent doesn’t give you a sense as to how long that snow water equivalent has been on the ground,” said Noah Molotch, an associate professor in the Institute of Arctic and Alpine Research (INSTAAR) at CU Boulder.
To gain more clarity, Hale developed a new measurement known as Snow Storage Index (SSI), which takes into account the timing and quantity of snowfall and snowmelt, both before and after April 1st. Unlike SWE, the SSI provides a more comprehensive understanding, encapsulating into a single number the time elapsed from when rain or snow falls in winter to when it becomes available as surface water.
The SSI gives a broader perspective on snow water storage. “The snow storage index allows us to look at snow water storage, not just in the context of how much is there at any given time, but the duration of that storage on the ground,” explained Molotch.
By using this tool, the researchers were able to study the performance of each mountainous region of the West as a water tower over the past 60 years, revealing a declining trend across the board.
High SSI values, close to 1.0, were found in places with a highly seasonal snowfall pattern. In the Cascades, for example, snow piles up during the fall and winter seasons and stays on the ground up to six months before it gradually melts in the spring and summer.
By Contrast, in Colorado’s Rocky Mountains, the SSI is lower – between 0 and 0.5—indicating snow both accumulates and melts during the colder half of the year.
Interestingly, areas like the Rockies and the Front Range, which are accustomed to this fluctuating pattern of snowfall and snowmelt, may find it easier to adapt to the declining snowpack water storage patterns linked with global warming.
However, the mountain regions near the West Coast, which heavily rely on snowpack meltwater during spring and summer, might face significant challenges when that water melts earlier and is not available during the late summer.
The researchers hope that this new SSI measurement will prove valuable for scientists and water resource managers, enabling them to make more accurate predictions and plan more effectively for the possibility of less water availability.
Half a century ago, the era of dam building enabled the Western United States to prosper with a reliable access to water for cities and agriculture, said Molotch. However, as these natural “water towers” of snow melt away, the reservoirs they filled may also deplete.
“The snowpack is eroding and disappearing before our eyes. That’s going to present challenges in terms of managing the infrastructure that’s allowed the Western United States to flourish over the last 100 years,” said Molotch.
Thus, as the snowpack continues to dwindle, managing water resources in the Western North America could become a complex puzzle, demanding innovation, forward thinking, and sustainable solutions.
Snowpack plays a critical role in both human and environmental water resources, especially in regions where a significant portion of annual precipitation falls as snow.
At its most basic level, snowpack refers to the accumulated snow that covers the ground in mountainous or high-altitude areas. During the colder months, the snowpack builds up, acting as a frozen reservoir.
As temperatures rise in the spring and summer, this snow melts, releasing water gradually into rivers, lakes, and the ground. This slow release of water over time is incredibly important for several reasons.
In many regions, especially in the western United States and Canada, snowpack is the primary source of water supply. As the snowpack melts in spring and summer, it replenishes reservoirs that provide drinking water to cities and towns. Without a healthy snowpack, there would be less water available during the driest parts of the year.
Many farming areas rely on the melting of snowpack to irrigate crops. The water that comes from melting snow travels down mountains into rivers and streams, which farmers then divert for irrigation. Without this reliable water source, agriculture in these areas would face significant challenges.
The flow of water from melting snowpack is also critical for hydropower, which generates electricity by using flowing or falling water to turn a turbine. In areas like the Pacific Northwest, hydropower accounts for a large percentage of electricity generation.
Snowpack is essential to maintaining healthy ecosystems. Many species of fish, for example, rely on the cold, clean water from snowmelt for spawning. Additionally, the slow melt of snowpack into the ground helps replenish groundwater, which many plants and animals rely on.
Changes in snowpack can serve as a useful indicator of climate change. Decreases in snowpack and earlier melt seasons can be linked to global warming. These changes can lead to water shortages, increased wildfire risks, and impacts on wildlife and ecosystems.
The reduction in snowpack and changes in snowmelt timing due to climate change pose significant risks to water resources. If less snow is falling and it’s melting earlier in the year, there may not be enough water available during the dry summer months when demand is highest. This could have serious implications for drinking water supplies, agriculture, energy production, and the health of our ecosystems.