About half of the freshwater which flows through the Amazon Basin is recycled and retained in the forest ecosystem. The Amazon Basin experiences high rainfall for all or most of the year. Precipitation ranges from 120 to 140 inches annually. Some areas, central Amazonia for example, experience approximately the same amount of rainfall throughout the year. Other regions, like the southeastern parts of the basin, have a dry season in the summer for two to three months.
Moisture is brought in from the Atlantic by southeasterly winds.
This moisture falls as rain on the highlands of Guyana. As the wind reaches the Andes, it rises and the moisture condenses, falling on the Amazon Basin where it drains into the rivers forming the Amazon. The lowland areas experience conventional rainfall patterns that bring very heavy precipitation. Through evapotranspiration, the rainforest adds huge amounts of moisture to the air. Heat from the ground warms the air, which then expands and rises.