Geoscience Reference
In-Depth Information
f igu r e 6. Snow surveyors measuring snow depth and water content in the Sierra
Nevada, California. (Photo by Doug Powell, courtesy of the Department of Geography
photo archives at the University of California, Berkeley.)
of water that will be generated when that snow melts (see i gure 6). Powell
could think of no better way to spend his winter months than in the high
Sierra Nevada, measuring the precious git that the mountains held in reserve
for the long, dry summer and fall months of the West.
Snow surveyors are still important today, but, since 1977, a consider-
able amount of data is collected by a network of instruments that have
been installed across the mountains of the West to forecast water supply.
h ese instruments automatically transmit the snow and climate information
they measure to a centralized computer system by radio telemetry. Changes
in daily snowpack are monitored, along with temperature, precipitation,
stream l ow, reservoir and groundwater levels, and soil moisture—all part
of an early warning system for l oods and droughts in the western United
States.
As we will discuss further in chapter 13, studies of changes in the snow-
pack over the past century reveal that the average snowpack has steadily
decreased by about 10 percent over that period, most likely due to warmer
temperatures. Climate modeling predicts that, by the end of the twenty-i rst
century, the snowpack could shrink by another 40 to 80 percent.
