The concept of a “rainy season month” is fundamental to agriculture, water resource management, and disaster preparedness in tropical and subtropical regions. While often discussed qualitatively, a rigorous definition requires quantitative meteorological thresholds. This paper examines the criteria used to define a rainy season month, focusing on precipitation totals, the onset and cessation phases, and spatial variability. Using case studies from the Indian Summer Monsoon and the West African Monsoon, this paper argues that a rainy season month is best defined as any calendar month where average precipitation exceeds a region-specific threshold (typically 50–100 mm) and potential evapotranspiration (PET) is exceeded by rainfall. The paper concludes by discussing the impacts of climate change on the shifting structure of the rainy season.
The rainy season is a transformative period that dictates the rhythm of life, agriculture, and travel across the globe. While many associate "rainy months" with gray skies, these periods are essential for replenishing the Earth's water supply and sustaining biodiversity. What Defines a Rainy Season?