Factors Affecting Rainfall Distribution:
Moisture supply to the atmosphere is the main factor in determining the amount of rainfall in any region.
Equatorial and rest of the tropical region have highest evaporation and hence highest supply of moisture.
Coastal areas have more moisture than interior parts of continents.
Frigid regions have very low evaporation hence very scanty precipitation.
Wind direction in the belts of trades and westerlies winds is very important.
Winds blowing from sea to land cause rainfall.
Land bearing winds are dry.
Winds blowing from higher to lower latitudes will get heated and give no rain while those blowing from lower to higher latitudes will get cooled and cause rainfall.
Sub-tropical deserts have very little rainfall because they have off-shore winds.
Ocean currents : Warm current are associated with warm moist winds which cause rainfal1, cold current have cold dry wind and hence no rainfall.
Presence of mountain across the direction of wind causes more rainfall on the windward side and creates rain shadow on the leeward side.
Areas of low pressure attract rain bearing winds while areas of high pressure do not.