People in the Mountains - Mountain Geography: Physical and Human Dimensions - page 502

where the periodic occurrences of the warm El Nino and the cold La Nina currents res-
ult in rainfall irregularities.
The complexities of amount, type, and timing of precipitation are reflected in moun-
tain ecosystems and in the lives of mountain people. Availability of precipitation-derived
moisture, along with temperature, sunlight, and soil conditions, influences crop choice,
timing of planting/harvesting, use of irrigation, and type of cultivation practices. Tim-
ing, location, and type of precipitation influence recreation and tourism, as in avoidance
of the wet monsoon season in the Himalaya and avoidance of winter snow for some
activities and its attraction for others. Precipitation in the form of snow is a very signi-
ficant factor in people's relationships with the mountain environment, acting as both a
resource and a hazard (Gardner 1986). However, its primary significance comes about
through its derivatives, snowcover or snowpack and glacier ice, discussed below.
Longer-term variation and change in precipitation present mountain people with
challenges of adaptation by adopting different crops and cropping systems, developing
new forms of tourism and recreation businesses, seeking out new water sources, avoid-
ing newly hazardous locations, moving away, and so on. Long-term adaptation to pre-
cipitation changes has been going on among mountain people for millennia. However,
the present urgency related to climate change and variability is driven by the fact that
economic and other dependencies on precipitation have grown with the populations of
mountain people and of the many living outside the mountains.
SUNLIGHT
The amount of sunlight, the primary energy source, received at any location in the
mountains depends on latitude, topography, and cloudiness. Thus, variation from place
to place and over time can be considerable. As the primary source of energy, sunlight,
or solar radiation, is fundamental in energy and moisture balances locally and region-
ally, and therefore exerts strong influences on vegetation and water, which are basic to
human use and occupancy. Topography plays a very significant role locally, some slopes
being more exposed to sunlight than others. On a slope facing into the sun, such as a
south-facing slope in the northern hemisphere or a north-facing slope in the southern
hemisphere, more direct solar radiation is received than on the slopes facing away from
the sun. These slopes tend to be sunnier, warmer, and drier than shaded slopes. These
differences are evident in the human use of opposing slopes. In the Alps, for example,
in longitudinal, west-east extending valleys, the traditionally preferred settlement and
agricultural sites are on the south-facing adrêt slopes (Peattie 1936; Fig. 10.10). The
north-facing ubac slopes have been avoided as traditional settlement areas, but are
favored locations for managed forests and ski runs. In equatorial mountains, where the
sun is nearly overhead most of the year, the differences in sunlight received on south-
facing and north-facing slopes are much less significant.