Aspect (geography) - Importance of Aspect

Importance of Aspect

Aspect can have a strong influence on temperature. This is because aspect affects the angle of the sun rays when they come in contact with the ground, and therefore affects the concentration of the sun's rays hitting the earth (amount of radiation divided by surface area, termed insolation).

The aspect of a slope can make very significant influences on its local climate (microclimate). For example, because the sun's rays are in the west at the hottest time of day in the afternoon, in most cases a west-facing slope will be warmer than a sheltered east-facing slope (unless large-scale rainfall influences dictate otherwise). This can have major effects on altitudinal and polar limits of tree growth and also on the distribution of vegetation that requires large quantities of moisture. In Australia, for example, remnants of rainforest are almost always found on east-facing slopes which are protected from dry westerly wind.

Similarly, in the northern hemisphere a south-facing slope (more open to sunlight and warm winds) will therefore generally be warmer and dryer due to higher levels of evapotranspiration than a north-facing slope. This can be seen in the Swiss Alps, where farming is much more extensive on south-facing than on north-facing slopes. In the Himalayas, this effect can be seen to an extreme degree, with south-facing slopes being warm, wet and forested, and north-facing slopes cold, dry but much more heavily glaciated.

For a farmer, thus, choosing an aspect that will shelter from hot, dry winds or from cold can be critical to successful growth of crops. Most farming agencies will state in manuals whether a crop prefers a poleward or equatorward aspect (if this is important). Glaciology is also influenced by aspect: unless precipitation patterns dictate otherwise (as in Iceland where glaciers accumulate on the much wetter southwestern side) glaciers always accumulate downwards on the poleward side of mountains.