Global Distribution of Rainfall
The global distribution of precipitation is influenced by the general circulation of the atmosphere, proximity to large bodies of water, and topography. Factors controlling the distribution of rainfall over the earth's surface are the belts of converging ascending air flow, air temperature, moisture bearing winds, ocean currents, distance inland from the coast, and mountain ranges.
The Earth's atmosphere is known to have regions characterized by large scale rising air, and other regions with descending air; these vary by latitude and by season. Rising air is found primarily near the equator and in the mid latitudes (40° to 60° North and South latitude), so these tend to be wet areas. Descending air dominates in the subtropics (20° to 30° North and South latitude) and the poles. The global distribution of precipitation shows that the wettest areas on Earth are in the "rising air" zones, while the driest areas (subtropical deserts and the even drier polar areas) are in the "descending air" belts
Zonal distribution of rainfall
Equatorial zone of maximum rainfall:
This zone extends upto 10° latitudes on either side of the equator characterized by warm and moist air masses. Rainfall occurs mainly due to convectional rainfall and mean annual ranges from 1750 mm to 2000 mm.
Trade wind rainfall zone:
This zone extends between 10-20 degree latitudes in both the hemispheres and is characterized by northeast and south-east trade winds. These winds yield rainfall in the eastern part of the continent as they flow over oceans and brings moisture. Thus, the western part of the continents becomes extremely dry and deserts
Subtropical zone of minimum rainfall:
This zone extends between 20-30 degree latitudes in both the hemisphere where descending air from above induces high pressure and winds thus results in anti cyclonic conditions
Mediterranean rainfall zone:
This rainfall zone extends between 30-40 degree latitudes in both the hemispheres where rainfall occurs through Westerlies and cyclones during winter season while summer seasons are dry.
Mid-latitudinal zone:
This zone extends between 40-50 degrees latitudes in both the hemispheres where rainfall occurs due to Westerlies and Temperate Cyclones.
Polar zone:
It extends from 60 degrees to pole in both the hemispheres. Precipitation mainly occurs in the form of snow.
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