Yuma Ag and You: Measuring the snowpack

Bobbi Stevenson- McDermott       February 5, 2017 publication

Love this Yuma weather, 65 one day, 85 degrees the next! Let’s enjoy the warmth and hope it gets cool again as it is too early for ‘winter’ weather to depart.

There continues to be lots of articles and commentary on the water situation in the West on a daily basis. Water is the lifeblood of the West-the crucial commodity. Have you ever wondered how the practice of water amount forecasting came about?

James E. Church was a real-life Indiana Jones. Born in Michigan in 1869, Church moved west in 1901 to teach classics and art history at the University of Nevada, Reno. The nearby Sierra Nevada fascinated him. He hiked there often, often publishing his mountaineering accounts in the Sierra Club newsletter. Around this time, water uncertainty was causing political friction in Tahoe. Lake Tahoe homeowners were suffering property damage from flooding and demanded the dam operators release water before the snow melted. People living and working downstream opposed this, because the water was their security against a dry spring and summer.

While his community battled over water levels, Church worked on a solution. Appreciating the relationship between snow and water supply, he knew if he could measure snowpack in surrounding mountains he could predict how much snowmelt would flow into Lake Tahoe. Such a forecast would empower dam operators to make informed water planning decisions.

No tool existed to efficiently measure water content in snow, so Church invented one. The Mt. Rose Sampler allowed him to quickly and consistently measure the water content of snow. Churches sampler was so well designed that it is almost identical to the modern Federal Sampler used by current snow surveyors. Starting in 1908, Church established a series of snow courses on the mountains surrounding Lake Tahoe. He calibrated his forecasts by comparing his measurements against the fluctuating levels of the lake. His method proved so useful it spread across the West. In 1935,, Congress formed the Federal-State Cooperative Snow Survey, now known as the Soil Survey and Water Supply Forecasting Program of USDA’s Natural Resources Conservation Service. Since the days of Church, snow survey has continued to expand and advance. Manual snow courses are steadily being augmented or replaced by automated SNOTEL sites. NASA has recently become involved measuring snowpack from above.

To the casual observer, the process by which we get water from the mountain snowpack is simple: the weather cools as winter approaches and precipitation changes from raindrops to snowflakes. Snow accumulates in winter and with the warming of spring and early summer it melts, producing stream flow. In reality, the relationship between the snowpack and the amount of snowmelt runoff is complex. It depends on many factors, primarily moisture content of the soil, ground water contributions, precipitation patterns, fluctuation in air temperature, use of water by plants and frequency of storm events. These factors change throughout the year and from year to year. Their relative importance varies depending on location.

It has been a very wet start to the snow season in Arizona as of January 2017. The total precipitation for the past month ranged from 162 percent to 264 percent of average in the major basins. Water supply varies greatly from season to season and from year to year, and water is often located great distances from where it is needed. Snowmelt from winter accumulations in the high mountains is the source of about 75 percent off the region’s water supply. Air temperature and availability of atmospheric moisture determine how wet or dry the snow is. Typically, the west slope of the Cascade Range, in response to the Pacific Ocean’s strong influence, receives heavy, wet snow. One foot of that snow, newly fallen can produce up to 1.5 inches of water. In other areas, such as the Wasatch Mountains in central Utah, the snow is much drier. It is light and powdery-excellent for skiing- and one foot of fresh snow pack might contain an inch of water.

For the farmlands of Yuma County, poor mountain snows on the Colorado River Basin can create shortages, celebrate the great winter the mountains are experiencing.