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Why does the southwest monsoon bring most of the annual rainfall to India and mainland Southeast Asia?

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A map of the continent of Asia, including its countries, boundaries, and capital cities, as well as parts of Europe, Africa, and surrounding oceans. — Asia Map showing the countries and national capitals of Asia.

The southwest monsoon is the primary source of annual rainfall for India and mainland Southeast Asia because it facilitates the transport of vast amounts of moisture-laden air from the Indian Ocean onto the continent.12

This phenomenon is driven by the seasonal heating of the Asian landmass. During the summer, the continent heats up more rapidly than the surrounding oceans, creating a large-scale zone of low pressure over southern Asia. This thermal contrast triggers a reversal in wind patterns: air flows from high-pressure cells over the ocean toward the low-pressure zone over the land. As these winds cross the ocean, they gather significant moisture.1342

The rainfall is intensified by several factors:
* Topography: When the moist airstreams encounter mountain ranges, they are forced to rise, leading to heavy orographic precipitation.54
* Convection: The moist air becomes unstable over the hot land, leading to rapid convection and the formation of towering clouds that produce heavy showers.56
* Atmospheric Disturbances: The presence of low-pressure waves and tropical cyclones within the monsoonal flow further enhances rainfall distribution.54