Alpine climate

Abstract

The climate of a steep equator facing slope? The climate in a poleward exposed avalanche track? The climate of an alpine observatory on a windswept ridge? The climate where alpine life occurs, e.g. in the surface of a cushion plant? In winter or in summer? Under overcast or clear sky conditions? In the tropics or in Alaska? Obviously THE alpine climate does not exist and meteorologists or biologists, a mountaineerer or a nematode in the soil will have different views on the subject, and a number of biased assumptions about the alpine climate can be found in the literature. Here are some classics:

• Solar radiation increases with altitude”. If one traces this assumption back to the original texts such as the one by Sauberer and Dirmhirn (1958) one finds with surprise an explicit statement that this conclusion only holds for standardized weather conditions such as a clear sky. When full data sets, including all weather conditions, were considered, most often no such trend was found because of altitudinally increasing cloudiness (Fig. 3.1).

• The alpine life zone is characterized by strong winds”. This is a typical temperate zone perspective and wrong in this general form. There are strong latitude and exposure effects, with some isolated mountains in temperate and polar latitudes being truely wind beaten, while some of the highest mountains in the world in the sub-tropics and tropics and the inner parts of larger mountain systems are commonly quite calm (Grace 1977, Barry 1981).

• Precipitation increases with altitude”. While true in some, mainly humid temperate zone mountains, this is certainly not true for many subtropical and tropical mountains which show a mid altitude maximum and reductions at higher elevations (Flohn 1974, Lauscher 1976).

• The alpine life zone is characterized by short growing periods”, clearly, again a view valid for extratropical mountains only. If this were a key determinant of alpine plant characteristics , we should not find such characteristics in tropical mountains. For instance, if the general phenomenon of treeline formation were linked to season length we should not find upper treelines in the rather constant climates of the tropics.