Snow water
equivalent (mm)
300
200
100
0
Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
Figure 4.11: Mean monthly snow water equivalent, a common
snow pack measurement, for Columbine Pass, Colorado from
1971 to 2000, showing a typical seasonal pattern in a mountain
environment.
Source: Based on data from the U.S. National Resources Conservation Service
snow stores water during the winter and then melts in the Impacts on agriculture – crops and animal
spring and early summer, creating peak stream flows in husbandry
the afternoon and an overall seasonal peak flow. In many
semi-arid mountain environments, snow melt buffers the The dramatic impacts of snow cover on vegetation also
transition into the dry summer season. Mountain snow is apply to agricultural crops. Gradual changes in snow
also a key source of groundwater, since a significant por- cover, as well as incidences of extreme snow events,
tion of the snow melt enters the soil and drains downhill can have a strong impact on crops both at the start and
into valley sediments
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. The timing, spatial distribution, end of the growing season. Snow typically disappears in
and volume of snow melt are critical for determining how the spring before the start of the growing season. If it
much water flows as surface runoff into rivers and lakes occurs during the growing season, snow can insulate
and how much becomes groundwater. Earlier snow melt crops from cold air or cause damage by freezing crops
across the western United States, for example, caused a or breaking off branches and stems. An early autumn
one to four week earlier runoff for mountain rivers and snow may prevent a farmer from being able to harvest
longer periods of summertime low-flow
84
. crops because snow can damage the plants, prevent
54 GLOBAL OUTLOOK FOR ICE AND SNOW