15. Global Climates 4. Altitude and Aspect


Smaller areas may experience special climatic conditions of their own. These local climates are influenced by altitude and aspect .


Altitude and Local Climate Altitude means height above sea level. The higher a place is, the colder its climate will be. Temperatures decrease by roughly 1 °C for every 150 m climbed. This decrease in temperature is called the lapse rate .


Ireland’s landscape is a mixture of reasonably flat land in the midlands and mountainous areas on the coastline. Compare the landscape map of Ireland on the left with the map displaying average temperatures across the country on the right. We can see a connection between altitude and temperature.


11 12 °C


10


Relatively flat land Mountainous land


3 4 5 6 7 8 9


Study the two maps in figure 10. What is the connection between mountainous areas and temperature?


10. The connection between altitude and temperature


Increased (higher) altitude also increases chances of rainfall. Annual amounts of precipitation increase by between 100 mm and 200 mm on exposed slopes for every 100 m rise in altitude.


Aspect and Local Climate Aspect is the direction in which a slope faces.


The sun rises in the east, travels in a southerly direction and sets in the west. For the northern hemisphere, this means that south-facing slopes are warmer than north-facing slopes.


Aspect will also affect precipitation levels. Slopes facing the sea experience sea winds and therefore higher levels of rainfall called relief rainfall . The slopes on the leeward (sheltered) sides are drier.


South-facing: longer periods of sunshine; better for settlement and growing crops


South-facing slopes receive far more sunshine than north-facing ones in the northern hemisphere


Leeward side


North-facing: longer periods in the shade; more suitable for forestry


11. The effect of aspect on climate 231


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