The wet season, monsoon season or rainy season is the time of year when most of a region's average annual rainfall occurs. It usually lasts one or more months. The term "green season" is also sometimes used as a euphemism by tourist authorities. Areas with wet seasons are dispersed across portions of the tropics and subtropics. When the wet season occurs during a warm season, or summer, precipitation falls mainly during the late afternoon and early evening hours. The wet season is a time when air quality improves, freshwater quality improves, and vegetation grows substantially, leading to crop yields late in the season.