Monsoon is a wind that shifts with the seasons, sometimes producing heavy rains and floods. Monsoons occur because air heats differently over different surfaces, such as the land and the ocean. During summer, for example, the sun heats the land’s surface far more than that of the ocean. The heated air over land rises and is replaced by cool, moist air flowing from the ocean. The air from the ocean rises as it moves onto land, and the moisture in it condenses, forming clouds and rain. In winter, the land cools much more than the ocean. Cool air over the land sinks, flowing to the ocean as a dry wind. For this reason, places with monsoons have a rainy season and a dry season. Notable monsoons occur over Southeast Asia, central Africa, southwestern North America, and the Amazon region of South America.
The Asian monsoon,
the world’s largest, occurs over Southeast Asia. The summer monsoon typically produces extremely heavy rain, causing flooding along the Ganges, Brahmaputra, and Mekong rivers. Monsoon winds over China create large, slow-moving thunderstorms that often produce devastating floods along the Yangtze River and its tributaries. Although monsoon floods can be destructive, the people of Southeast Asia depend on monsoon rains for water. Unusually wet or dry monsoons can destroy crops and livestock and disrupt the region’s economy. See Asia (Climate).
The African monsoon
blows over west central Africa and the Sahel, a drought-plagued region south of the Sahara. People living in the dry Sahel depend on the monsoon rains for survival.
The North American monsoon,
also called the Arizona monsoon or Mexican monsoon, blows over much of the southwestern United States and northwestern Mexico. Summer monsoons can produce heavy rains, hail, strong gusty winds, and even flash floods.
The South American monsoon
is driven by summer heating over the high deserts of Chile, Argentina, Bolivia, Peru, and Ecuador. This monsoon spreads moisture and rainfall from the tropical Atlantic Ocean over the Amazon and into northern Argentina and Uruguay.
