No rainforests are too rainy. Rainforests are defined by their high rainfall, which is essential for the lush plant and animal life that thrives there. The average rainfall in a rainforest is between 100 and 400 inches per year, and some rainforests receive as much as 600 inches per year. This rainfall is what creates the humid, warm climate that is characteristic of rainforests. Without this rainfall, rainforests would not exist.