A monsoon is a seasonal reversal of wind patterns that brings dramatic shifts between wet and dry seasons. Monsoons are the primary source of water for billions of people in South and Southeast Asia.
Monsoons are large-scale seasonal wind reversals driven by differential heating between continental land masses and adjacent oceans, producing a pronounced wet season alternating with a dry season. The most well-known is the South Asian (Indian) monsoon, which brings approximately 70-80 percent of the region's annual rainfall between June and September as moisture-laden winds from the Indian Ocean flow northward over the subcontinent. Other significant monsoon systems include the East Asian, West African, Australian, and North American monsoons. The onset, duration, and intensity of monsoon rainfall vary considerably from year to year, influenced by factors including sea surface temperatures, El Nino-Southern Oscillation, the Indian Ocean Dipole, and land surface conditions. Monsoon variability has profound impacts on agriculture, water supply, hydropower generation, and flood risk for billions of people. Excessive monsoon rainfall causes devastating floods, while monsoon failures lead to drought and crop loss. Climate change is projected to intensify monsoon precipitation in many regions while increasing variability, making water resources management more challenging. Accurate monsoon forecasting is a high priority for meteorological services in affected regions, combining statistical methods with dynamical climate models.