Monsoon

A monsoon is a seasonal weather system that brings a clear change in wind direction and rainfall at certain times of the year. The word comes from an Arabic term meaning "season." Monsoons are not simply heavy rainstorms. They are large patterns of winds that last for months and affect wide areas. These winds often bring a rainy season followed by a dry season.

Monsoons happen because land and ocean heat up at different speeds. During warmer months, land becomes hotter than the nearby ocean. Warm air over land rises, which lowers air pressure. Cooler, moist air from the ocean then moves toward the land. This movement of air is called wind. When the moist air rises, it cools and forms clouds, leading to rain. In cooler months, the pattern reverses, and dry winds blow from land toward the ocean.

The most well-known monsoon occurs in South Asia. The South Asian monsoon affects countries such as India, Pakistan, Bangladesh, Sri Lanka, and Nepal. It usually begins in early summer and lasts several months. During this time, many areas receive most of their yearly rainfall. Rivers fill, soil becomes wet, and landscapes change quickly. When the rainy season ends, the region enters a drier period.

Monsoons also occur in other parts of the world. East Asia has a monsoon that affects China, Korea, and Japan. Parts of Africa experience seasonal monsoon winds, especially in West Africa. Northern Australia also has a monsoon season that brings heavy rain. Each region’s monsoon is shaped by local geography, such as mountains, oceans, and distance from the equator.

Monsoon rainfall can vary from year to year. Some seasons bring normal rainfall, while others bring very heavy rain or much less than expected. Too much rain can cause floods, which happen when water covers land that is usually dry. Too little rain can cause drought, a long period with little or no rainfall. Scientists study monsoons to better understand weather patterns and seasonal changes.

Monsoons have been observed and recorded for thousands of years. Ancient sailors depended on monsoon winds to travel across the Indian Ocean. By understanding the timing of the winds, ships could sail in one direction during one season and return in another. Today, monsoons remain an important part of the global climate system and continue to shape weather across many regions.