When snow arrives in the mountains, winter sports enthusiasts get excited. And, farmers “down country” get excited, too, but not for all the same reasons!
Winter mountain snows mean that come springtime, water supplies will be replenished for both urban and agricultural use. And, this year’s near-record snowfalls mean good things for Earth’s water cycle.
Yes, winter snows can be fun. But they are an important part of the water cycle, too. When we think of the earth’s water sources, we usually think of rainfall. However, the Western United States, in particular, receives the majority of its precipitation during the winter months. In the mountains, it’s usually in the form of snow, but in 2017, there also have been record rainfalls, too.
Accumulated winter snow, called snowpack, becomes a major source of drinking and irrigation water for many Americans.
Snowpack is the result of many layers of compressed snow. The layers accumulate over the winter in high altitude environments. The prolonged periods of cold weather allow snowpack to get to depths of up to a foot or more. Snow accumulates in the winter and then feeds streams, rivers, and groundwater in warmer months.
Areas like the Central Valley in California, the Colorado River Basin, and the Rio Grande Basin rely on snowmelt from winter snowpack. They use it for municipal, agricultural, and industrial purposes. Snowpack volumes in the Sierras of California can average 18.6 cubic kilometers a year. That’s 4.9 trillion gallons of water!
Recent droughts and warmer temperatures in the Western United States have put a closer focus on snowpack levels and how much we rely on it as a source of water. The impacts of decreased water storage from less snow melt and snowpack could lead to major shifts in how we depend on and use our water resources.
In springtime, water from melting snowpack is distributed in one of two ways. Snow melt can enter the soil surface via infiltration or it can move over the surface as runoff. The timing and rate at which snow melts makes all the difference between these two processes.
Thawed, semi-moist soils are the perfect “sponge” for melting snow. Slowly melting snow flows into the soil profile. Small pores, either micro or macropores, and channels, help the water soak down to the water table. This “surface infiltration” also aids in supplying plant roots and micro-organisms with much needed moisture for spring growth and soil fertility. The water will slowly move through the soil surface and eventually flow to bedrock and then into local aquifers. For further information about soil hydrology, see our May 2016 post “how does water move through soil.”
When the soils are either still frozen, or saturated with water, snowmelt will flow over the soil. In these cases, water can form quickly-running, temporary downhill streams. This process can lead to environmental damages, including soil erosion and sedimentation along the water’s path to lower ground.
Snowpack and snow melt are critical parts of the water cycle, particularly in the Western United States. Many of the crops Americans depend on come from areas that are fed by snowmelt from high-altitude environments. Snowmelt also plays an important role in “groundwater recharge” and the water balance of aquifers. The beauty of those states was even impacted long ago by the accumulation, thawing, and distribution of snow! It is critical to both the natural environment and society that this snow melt reaches our aquifers, groundwater tables, and surface bodies of water. That way, we can continue to use, drink, and enjoy the water that is available in these sensitive areas.
By James Hartsig, Duraroot
Contributing research provided by Mary Tiedeman, Florida International University
Snowpack depth Sierras https://www.nohrsc.noaa.gov/nsa/?region=Sierras