World distribution of rainfall

Rainfall varies from place to place and season to season. General patterns:

• Rainfall decreases steadily from the equator towards the poles.
• Coastal areas get more than continental interiors.
• Oceans get more than land, being great sources of water.
• Between 35° and 40° N and S, rain is heavier on the eastern coasts and decreases towards the west.
• Between 45° and 65° N and S, the westerlies bring rain first to the western margins of the continents, decreasing towards the east.
• Where mountains run parallel to the coast, rain is greater on the coastal plain (windward) and less on the leeward side.

Rainfall regimes (annual totals):

• Over 200 cm: the equatorial belt, the windward slopes of mountains along western coasts in the cool temperate zone, and the coastal areas of monsoon lands.
• 100-200 cm: interior continental areas and continental coasts receive moderate rain.
• 50-100 cm: the central parts of tropical lands and the eastern and interior parts of temperate lands.
• Under 50 cm: rain-shadow areas in continental interiors and high latitudes.

Seasonal distribution matters for how useful rain is. Some regions get rain evenly through the year, such as the equatorial belt and the western parts of cool temperate regions.

Example (new): Cherrapunji's hills, facing moist monsoon winds from the Bay of Bengal, are among the wettest places on earth, while Leh, cut off behind the Himalayas in a high, dry interior, gets well under 50 cm a year.