Mountain Climate - Mountain Geography: Physical and Human Dimensions - page 128

The spatial resolution of most weather station networks in mountains is far too
coarse to capture the spatial variability of their microclimates. Maps of climatic vari-
ables are often interpolated from existing meager data sets, using assumed or empirical
relationships with elevation (Kyriakidis et al. 2001; Horsch 2003; Minder et al. 2010).
These models are unable to demonstrate local deviations in trends, and when combined
with map scale, microclimates are typically eliminated from most maps of mountains.
Likewise, vegetation maps of mountainous areas rarely show the small patches of veget-
ation that occur in micro-climatic habitats. While these features may be unmappable,
they are certainly observable in mountains, adding to the splendor of the multifaceted
mountain environment.
Climate Change and Variability
The variability of climatic phenomena is an important natural component of the Earth's
climate system. Climatic variability (i.e., occurrence of certain climatic events) is differ-
ent than climate change, which is a permanent change in climatic conditions. However,
changes in variability are one likely result of climatic change. The middle and high lat-
itudes inherently have especially variable climates since they are influenced by large
seasonal changes in energy. The equatorial region experiences little variability, as it has
nearly the same energy fluxes year round. Reflecting the complexity of the climate sys-
tem, most regions of the world show different patterns and magnitudes of variability
and trends through time (Viles and Goudie 2003).
All temporal climate records demonstrate some degree of interannual variability
(e.g., Beniston et al. 1997; Liu and Chen 2000; Kane 2000; Viles and Goudie 2003; Xie
et al. 2010). Every mountain location has its record high and low temperature, snow-
fall, rain event, drought, and wind speed (Cerveny et al. 2007). While these extreme
events are rare, they often occur with a greater frequency, and with more extreme mag-
nitudes in mountainous regions, than in lowlands (Frei and Schär 2001). Extreme storm
events are exacerbated by the topographic setting of mountains, producing even high-
er precipitation totals, lower temperatures, and higher wind velocities. As discussed
in Chapter 10, extreme precipitation events in mountains are of significance because
they lead to hazards such as downstream flooding, soil erosion, and mass movements on
slopes. Temperature, precipitation, and resulting runoff are often related to distant for-
cing mechanisms, such as the El Niño/Southern Oscillation (Cayan et al. 1999; Diaz et
al. 2001, 2003; Clare et al. 2002; Rowe et al. 2002). Several other periodic, yet chaotic,
perturbations to the climate system have been linked to increased climatic variability
(Fowler and Kilsby 2002; Viles and Goudie 2003).
Among the regional differences in variability, the following consistent temporal
trends emerge in data sets over the last century: (1) The number of extremely warm
summer temperatures has increased; (2) the number of extremely cold winter temper-
atures has decreased (with fewer frost days); and (3) mean summer season precipita-
tion has increased—in particular, an increase in heavy precipitation events (Viles and
Goudie 2003). All of these general trends have temporally reversed during the period of
record, so that while variability is expected, changes in the frequency of occurrence of
extreme events are recognized as a signal of ongoing climate change (Diaz et al. 2003).
The variations in the climate system, especially decadal- to millennial-scale oscillations,