page_title: Aspect (geography)
section_title: Importance of aspect
hierarchical_section_title: Aspect (geography) / Importance of aspect
caption_attribution_description: English: Effects of aspect on vegetation can be clearly seen in this photo from Southwest Idaho near Anderson Ranch Reservoir. The north facing slopes receive more snow often because of prevailing winds and are shaded from direct sunlight during the winter, consequently they have more water available to support trees and forests, while the south facing slopes which receive more insolation is much hotter and dryer and supports only smaller more desert adapted woody plant species. North facing slopes here are dominated by a Pinus ponderosa, Pseudotsuga menziesii forest while the south facing slopes are mainly dominated by desert shrubs Artemisia tridentata and Purshia tridentata.
context_page_description: In physical geology, aspect is the compass direction that a slope faces. For example, a slope on the eastern edge of the Rockies toward the Great Plains is described as having an easterly aspect. A slope which falls down to a deep valley on its western side and a shallower one on its eastern side has a westerly aspect or is a west-facing slope. The direction a slope faces can affect the physical and biotic features of the slope, known as a slope effect. The term aspect can also be used to describe the shape or alignment of a coastline. Here, the aspect is the direction which the coastline is facing towards the sea. For example, a coastline with sea to the northeast has a northeasterly aspect.
context_section_description: Aspect can have a strong influence on temperature. This is because of the angle of the sun in the northern and southern hemispheres which is less than 90 degrees or directly overhead. In the northern hemisphere, the north side of slopes is often shaded, while the southern side receives more solar radiation for a given surface area insolation because the slope is tilted toward the sun and isn't shaded directly by the earth itself. The further north or south you are and closer to winter solstice the more pronounced the effects of aspect of this are, and on steeper slopes the effect is greater, with no energy received on slopes with an angle greater than 22.5° at 40° north on December 22 (winter solstice).
  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 drier 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.
caption: Effects of aspect on vegetation can be clearly seen in this photo from Southwest Idaho near Anderson Ranch Reservoir. The north facing slopes receive more snow often because of prevailing winds and are shaded from direct sunlight during the winter, consequently they have more water available to support trees and forests, while the south facing slopes which receive more insolation are much hotter and dryer and support only smaller more desert adapted woody plant species. North facing slopes here are dominated by a Pinus ponderosa, Pseudotsuga menziesii forest while the south facing slopes are mainly dominated by desert shrubs Artemisia tridentata and Purshia tridentata.
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