Environmental Engineering Reference
In-Depth Information
Plate 25.3
Rime ice coating the windward side of a
meteorological screen and buildings, deposited by
sublimation in a cold moist airstream. Photo: Ken Addison.
Orographic effects may be greater in winter, and individual cells within frontal systems
are capable of 'dumping' rain at rates of, or even above, 50-200 mm hr
−1
. The effect is
confirmed by precipitation maxima in or just to the leeward of ranges, followed by
downwind rain shadows. Tropical coast mountains such as Kauai (Hawaii) and the
Dorsale range (Cameroon) experience among the highest global precipitation rates at
11,000-12,000 mm a
−1
. British Columbian and Alaskan coast ranges receive 2500-5000
mm a
−1
, falling to 500 mm and 1250 mm respectively within 100 km downwind. Much of
this precipitation falls as snow by virtue of their altitude and latitude, and regional
snowlines also reflect rain shadows, rising from 1·6 km on the west side of southern
British Columbia coast ranges to 2·9 km inland and 3·1 km in the eastern Canadian
Rockies. In Europe snowlines rise from 1·7 km in Scandinavia to 3·3 km in central
Europe and hover just above semi-permanent snowbeds at 1·3 km on Ben Nevis and the
Cairngorms in Britain. Global snowlines range from sea level in polar areas to 4·5 km in
moist equatorial regimes such as the Ecuadoran Andes, rising above 6 km in the dry
Andes and Tibet (Figure 25.8).
MOUNTAIN CLIMATE
So far we have looked at systematic effects, with important consequences for regional
snowline elevations and plant growth. Substantial local variations are imparted by
