Why, in some parts of Earth, rain falls in huge amounts
while in other parts of Earth rain does not fall at all?
Rain is influenced by wind currents and topography. When moist winds
strike mountain ranges, the air is forced to ascend, and the moisture falls
out of the clouds as rain or snow. In some areas, the winds contain very
little moisture, and no precipitation can fall. Areas receiving less than
10 inches of rain in a year are classified as deserts.
Factors other than topography cause rain also...such as fronts, which
cause moist air to ascend. But when there is little or no moisture in the
air, for whatever reason, precipitation is unlikely.
Wendell Bechtold, meteorologist
Forecaster, National Weather Service
Weather Forecast Office, St. Louis, MO.
The weather, whatever the parameter such as temperature, humidity, rainfall,
etc. is mostly dependent on climate and climate is greatly dependent on the
geography and topography of the area.
Rainfall is heavier in areas where there is abundant atmospheric moisture,
as in the tropics, near an ocean coastline, near an area of an ocean where
there are seasonal monsoon rains (southeast Asia for instance), etc.
Little rainfall occurs where there is little available moisture because an
is located far from an ocean (Sahara desert for instance), or is in the
mountains (moisture "rains" out on the leading side of the mountains, leaving
the air "dry"), or is too cold (Arctic regions are cold deserts).
David R. Cook
Atmospheric Physics and Chemistry Section
Environmental Assessment Division
Argonne National Laboratory
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Update: June 2012