Natural Elements Affecting Climate

Various factors prevent climatic regions from occurring in simple latitudinal bands; one such factor is the nature of the terrain.

Mountains, for example, have a considerable influence on climate because they act as barriers to the wind and also because temperatures decrease with increasing altitude (by about 6.5°C for every 1,000m increase in height).

The windward sides of many mountains are rainy, whereas the leeward sides are in a rain shadow and are relatively dry.

The highest mountains also affect movements of air in the upper troposphere; for example, the westward-flowing jet stream rises and veers northward over the Rocky Mountains of North America, then turns southwards again on the far side. The effect is to maintain relatively warm air over the Rockies at a high level.

The configuration of the continents and prox­imity to the ocean are also important, because large expanses of water (including lakes) tend to mod­erate the climate; thus lakeside and coastal loca­tions usually have less extreme climates than do places in the center of a continent.

This moderating influence of water is generally greatest near the ocean, which not only retains heat more readily than does land, but also transports it. Hence warm and cold ocean currents play a major part in deter­mining the climates of coastlands.

The development of maritime and continental air masses is another factor that influences climate dramatically, which is exemplified when seasonal changes cause reversals of wind directions, or monsoons.

Monsoon climates are most marked in southern Asia, where rapid cooling in winter causes the development of a high-pressure air mass over the land. From this air mass blow the dry north-east­ern Trade Winds.

In spring, the northward move­ment of the Sun causes northern India to be heated and, as a result, a marked low-pressure sys­tem develops into which south-eastern Trade Winds are sucked across the equator, changing direction as they do so to become moist Westerlies.