Mountain Climate - Mountain Geography: Physical and Human Dimensions - page 86

FIGURE 3.9 View of an east-west valley near Davos, Switzerland, showing settlement and clearing on
the sunny side (south-facing), while the shady side (north-facing) is left in forest. (L. W. Price.)
VERTICAL TEMPERATURE GRADIENT
Change of temperature with elevation is called the environmental or normal lapse rate.
De Saussure, who climbed Mont Blanc in 1787, was one of the first to measure temper-
ature at different elevations. Many temperature measurements have since been made in
mountains around the world. The lapse rate varies spatially according to many factors.
Nevertheless, by averaging the temperatures at different levels, as well as those meas-
ured in the free air by balloon, radiosonde, and aircraft, average lapse rates have been
established, ranging from 1°C to 2°C (1.8°F to 3.6°F) per 300 m (1,000 ft) (Minder et al.
2010). Aside from purposes of gross generalization, however, average lapse rates have
little value in mountains. There is no constant relationship between altitude and tem-
perature across space or time. Instead, the lapse rate changes continually with chan-
ging conditions, particularly the diurnal heating and cooling of the Earth's surface. For
example, the vertical temperature gradient is normally greater during the day than at
night, and during the summer than in winter. The gradient is steeper under clear than
under cloudy conditions, on sun-exposed slopes than on shaded ones, and on contin-
ental mountains than on maritime mountains (Peattie 1936; Yoshino 1975). Also, the
characteristics of free-air temperature differ from those on a mountain slope (Pepin and
Losleben 2002), though the higher and more isolated a mountain peak is, the more
closely its temperature will approach that of the free atmosphere.
Table 3.3 presents the average decrease of temperature with changing elevation in
the Alps, and Figure 3.10 illustrates temperature changes with elevation in the Cascade
Mountains of the United States. The temperatures shown are averages, with some in-
terpolation between stations; the actual decrease with elevation is much more variable,