There are two kinds of upward air deflections. Orography deflects large scale horizontal flow in the upward direction. Daytime heating of mountain surface also causes an upward air flow. By that moist air propagates in vertical upward direction along the orographic slope. These types of wind are called anabatic winds. Orographic precipitation is a result of this anabatic wind flow. After the lifting of air is completed the air is expanding in big size and gets cool. This air cooling is known as adiabatic cooling rising moist air. When the temperature of the rising air gets lower than its dew point temperature, then condensation takes place.

The water vapor within the air gets condensed by the temperature? After the condensation of air clouds are formed. If in the cloud there is more than enough water vapor droplets of water are formed. Next if the droplets become large enough and gain some weight then they fall to ground as precipitation. Orographic precipitation is a special kind of precipitation. Mountain Areas with a consistent air flow have two types of climate sides, a wetter climate in the windward side of a mountain and a drier side in the leeward side of a mountain. In the leeward side of the mountain a rain shadow is formed. Amount, intensity, duration and time of precipitation is fully depending on orography. There are three important contributors for the orographic precipitation. They are slope steepness of the mountain, width of the barrier, humidity of air and updraft speed of the water vapor.

Oceanic islands know orographic precipitation very well. New Zealand and Hawaiian island are two countries where most rainfall is received by the windward side. In the other side which is known as leeward side there is no rain. As a result of it that side becomes quite dry and looks like a desert. This happening results differences in the gradient of average rainfall in these countries. In the coastal areas average rainfall is about 500 to 800 mm per year whereas in the interior uplands average rainfall becomes over 2500 mm per year. But areas in the leeward side face problem when the rainfall is concerned. Average rainfall in these areas is below 450 mm per year. Some cities and areas at the top of high uplands are too much welled of rain as the average rainfall in those parts is over 12000 mm per year.