Why do mountainous area receive higher rainfall?

Question

Why do mountainous area receive higher rainfall?

Answer 1

When air rises, it cools.  When it cools, the amount of water the air can hold is reduced.  the water (humidity) condenses out and forms clouds and precipitation.  Typically, the precipitation increase is seen primarily on the upwind side of the mountains.  Obviously if your mountain system is down wind from a dry plain or desert, this effect is much less pronounced because the air is already dry (there isn't really any water to condense out on cooling).

Answer 2

Because clouds have moisture in them and when they brush against mountains, that moisture percipitates out as rain because of the temperature difference between the cloud and the ground, which is warmer than the clouds.

Answer 3

Mountain areas are the best location for orographic lifting, which is a very effective lifting mechanism. If a warm and humid air mass were to be raised up a mountain side, the moisture would then be condensed and precipitation would form in large quantities. Also, frontal boundaries tend to stall out in mountain areas, which would develop a stationary front. A stationary dumps a lot of precipitation.