The climatic snow limit in mountains is that line where perennial snow occurs. It depends on budget of snow melting, and, consequently, on air temperature, solid precipitation amount and solar radiation income as varied with different slopes. For instance, the mean air temperature at the snow limit T₀ in Norway is equal to +6ºC by permanent cloudy sky and total precipitation about to 2000 mm. In opposite, in Chilean Andes with their extreme high solar radiation income, we can found the snow limit by T₀ = -2º

Actual snow limit may not be in a close agreement with the climatic one, because it is a product of continual interrelations between some steady climate and current weather by complex mountainous relief. The highest and the lowest altitudes of the snow limit are so different at the middle latitudes of northern Hemisphere as nowhere else (Table 2).

Table 2. The altitudes of snow limit in mountains of Northern Hemisphere (Blutgen, 1966)

In humid western Georgia (Caucasus) the snow limit descends to about 2500 m and lower, while in semi-arid mountains of Dagestan it elevates to 4000 m above sea level. Ski-sliders (as well as the author too) can look at these aspect-related influences from a cable lift to the mount Elbrus in Central Caucasus. Both precipitation and snow water equivalent are usually enhanced with elevation, and respective gradient varies from 15-25 mm per each 100 m height in semi-arid mountainous regions such as Altai Mts. (south-central Siberia) to 40-70 mm per 100 m in humid Italian Alps and even to 85 mm per 100 m for the southern slope of Caucasus. There are the highest precipitation rates at elevation zones just beneath the snow limit. That precipitation galore is gainful for the deep thickets of relict spruce on western Georgian mountain slopes, and can promote there for snow avalanches of the highest magnitude.

Exposure-related variations in snow water equivalent are of great importance. They are right "life support system" for wide regions in Central Asia. There are productive agriculture and horticulture there: cotton plantations, orchards and vineyards, and vegetable plants such as well known sweet melons from Bukhara. All this abundance exists only due to irrigation using the streams which feed by snow melt water flowing from the Tian' Shan' ridges. As was found by observation, the runoff depth by the time from May to September on a basin situated at 3400 m a.s.l. on the southern slope of the ridge is 1300 mm, while similar basin of mainly northern aspect at the same elevation produces 2000 mm melt water and more.

A similar effect is observed by a journey across southern Siberia and Mongolia that depends on atmospheric circulation and particularly expresses there in a semi-arid climate. There are only dry prairies with larch groves sparsely grown on the south-faced slopes and, in opposite, the pine and fir tree stands that is good for timber covered the north-faced ones. Alike is on the American Rocky Mountains (on east- and west-faced slopes respectively) in Idaho and Wyoming States.

Hydrosphere © 1990 — 2005 Vladimir A. Shutov
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