The monsoon (from the Arabic mawsim, meaning season) is a large-scale seasonal wind reversal accompanied by dramatic changes in precipitation. The most famous is the South Asian monsoon, which brings the summer rainy season to India and Southeast Asia (June–September), but monsoon circulations exist in West Africa, Australia, East Asia, and even North America. Monsoons are driven by the differential heating of continents and oceans across seasons.
In summer, continents heat faster than oceans, creating a thermal low over land that draws in moist maritime air. As this air rises over heated terrain, it condenses and produces torrential rainfall. The Indian monsoon delivers 70–90 % of India's annual rainfall in just four months, making it critical for agriculture and water resources for 1.5 billion people. When the monsoon fails or is significantly delayed, the consequences include crop failure, water shortages, and economic crisis.
In winter, the process reverses: the continent cools faster, high pressure develops over land, and dry air flows outward toward the warmer ocean — the dry or winter monsoon. This seasonal oscillation in wind direction (roughly 120° or more) distinguishes monsoons from other rainfall patterns. Although Spain does not experience a true monsoon, its climate is influenced by the West African monsoon through the position of the Intertropical Convergence Zone, which affects Saharan dust transport and trade wind patterns. Climate models suggest that climate change may intensify monsoon rainfall extremes while also increasing drought periods between monsoon pulses.