Geography Reference
In-Depth Information
CHAPTER THREE
Mountain Climate
ANDREW J. BACH and LARRY W. PRICE
Climate is the fundamental factor in establishing a natural environment, setting the stage
on which all physical, chemical, and biological processes operate. This becomes espe-
cially evident at the climatic margins of the Earth, namely desert and tundra. Under tem-
perate conditions, the effects of climate are often muted and intermingled, so that the
relationships between stimuli and reactions are difficult to isolate, but under extreme
conditions such relationships become more evident. As extremes constitute the norm in
many areas within high mountains, a basic knowledge of climatic processes and charac-
teristics is key to understanding the mountain milieu.
In mountain areas, great environmental contrasts occur within short distances as a
result of the diverse topography and highly variable nature of the energy and moisture
fluxes. While in the mountains, have you ever sought refuge from the wind in the lee of a
rock? If so, you have experienced the kind of difference that can occur over a small dis-
tance. Near the margin of a species' distribution, such differences may decide between
life and death; thus, plants and animals reach their highest elevations by taking advant-
age of microhabitats. Great variations also occur within short time spans. When the sun
is shining, it may be quite warm, even in winter, but if a passing cloud blocks the sun,
the temperature can drop rapidly. Therefore, areas exposed to the sun undergo much
greater and more frequent temperature contrasts than those in shade. This is true for all
environments, but the difference is much greater in mountains because the thin alpine
air does not hold heat well and allows more solar radiation to reach the surface.
More generally, the climate of a slope may be very different from that of a ridge or val-
ley. When these basic differences are compounded by the infinite variety of combinations
created by the orientation, spacing, and steepness of slopes—along with the presence of
snow patches, shade, vegetation, and soil—the complexity of climatic patterns in moun-
tains becomes truly overwhelming. Nevertheless, predictable patterns and characterist-
ics are found within this heterogeneous system; for example, temperatures normally de-
crease with elevation while cloudiness and precipitation increase; moreover, it is usually
windier in mountains, the air is thinner and clearer, and the sun's rays are more intense.
The dynamic characteristics of mountains also have a major impact on regional and
local airflow patterns that affect the climates of adjacent regions (Xu et al. 2010). Their
influence may be felt for hundreds or thousands of kilometers, making surrounding areas
warmer or colder, or wetter or drier, than they would otherwise be. The effect of the
mountains depends upon their location, size, and orientation with respect to the mois-
ture source and the direction of prevailing winds. The 2,400 km (1,500 mi)-long barrier
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