Mountain barriers force the moisture- bearing winds to ascend, so that condensation and precipitation occur. The precipitation is concentrated on the windward slopes, and a rain shadow is produced on the leeward.
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All over the world, wherever the prevailing winds blowing from the oceans to the land are blocked by mountain ranges or plateaus, copious rainfall results on the windward slopes.
Even in tropical regions, orographic lifting is one of the main factors for record annual rainfalls. However, upper-air subsidence, as in trade-wind inversion, is not conducive to precipitation at high altitudes.
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The summer monsoon in India produces heavy rainfall on the southern slopes of the Himalayas. The areas to the north of the Himalayan ranges are deprived of precipitation.
Similarly, the western slopes of the Western Ghats receive about 200 to 250 centimeters of precipitation from the south-west monsoon, while the state of Karnatak and other adjoining areas being in the rain-shadow receive only a meager rainfall and remain practically dry.
The Atlas Mountains of Africa, the Andes mountain ranges along the coasts of Chile and Argentina, the Southern Alps of New Zealand and the mountain ranges of Western North America offer the best examples of the effects of mountain barriers on precipitation distribution.
The vertical distribution of precipitation is also controlled by the mountains, which has already been discussed in connection with orographic precipitation.