While the temperature remains constant throughout the year in tropical forests, rainfall varies dramatically, depending both on time of year and location. There is usually a pronounced rainy season, often accompanied by extensive flooding, and a dry season, during which many trees shed their leaves if too little water is available. While the seasons in a tropical forest are based on rainfall and not temperature, they still have a definite impact on the plants and animals in the region.

Mt. Waialeale, Hawaii, receives the most rainfall on earth, averaging 11,981 mm (472 inches) every year! During a dry season in the rainforest, less than 10 mm (3.9 inches) of precipitation fall during a month.