It rains abundantly in rainforests because most rainforests are located around the earth's equator, which has a humid and warm climate. A forest must receive at least 75 inches of rain per year to be considered a rainforest.
Conventional wisdom attributes rainforests' considerable rainfall to warm, humid climates, but another theory suggests that forests are not rainforests because they receive a lot of rain; rather, they receive a lot of rain because they are rainforests which, by their nature, attract water that becomes rain.
According to this theory, a rainforest acts as a biotic pump, attracting water vapor. This water vapor condenses and turns to rainfall. In turn, the air pressure decreases, pulling in even more water vapor and driving the cycle. Not only does this theory suggest that forests are important to rainfall, but it also means that those rainforests are critical to the global water cycle.
Rainforests can be tropical or temperate. Both types receive at least 75 inches of rain per year, but temperate rainforests have cooler temperatures. Tropical rainforests lie in the equatorial regions of the world, particularly South and Central America, the Caribbean, Asia and Africa. Temperate rainforests are located farther north, in the Pacific Northwest.