What Is the Average Rainfall in a Rainforest?

Rainforests have more average annual rainfall than any other biome. The amount of rainfall in a deciduous forest is the closest to the rainforest, and receives a third less rainfall annually, on average, than a rainforest. In recent years, efforts to prevent destruction of the rainforest through deforestation have stepped up. However, the earth's rainforests have already shrunk significantly. The rainforest cannot exist without its trees. This essential ecosystem depends on trees for the very element that makes this type of forest a rainforest -- rain.

Features

Rainforests are characterized by heavy annual rainfall, thick vegetation and diverse plant and animal species. At a minimum, a rainforest receives 80 inches of rainfall annually. Most receive much more. The state of Kentucky, by comparison, receives an average of 40 to 50 inches of rain per year. This means even the driest of rainforests get twice the rainfall Kentucky does. Rainfall amounts in the rainforest are relatively equal throughout the year, though some have one slightly wetter month per year. In the rainforest, it rains more than half the days of the year, every year.

Function of Trees

Deforestation affects the rainfall amounts in some rainforests, though efforts to decrease deforestation have recently been undertaken. Rainforests behave differently than other biomes. They exist as nearly closed systems, with much of their rainfall coming from water that is recycled throughout each day through the rainforest water cycle and transpired from the lush growth of trees. Tropical rainforests, in particular, have been affected. Because they are located near the equator, their temperatures remain consistently warm. The thick tree growth combined with warm temperatures and high humidity in the air from evaporation provide a cycle that produces as much as 50 to 75 percent of its own rain daily. Trees play an important part with transpiration and by shading the rain-soaked ground, which keeps humidity high. Without the right amount of trees, rain lessens, vegetation dies, and the rainforest's existence is threatened.

Tropical Rainforests

Tropical rainforests grow near the equator, where the warmth of the sun and the length of daylight are constant. Temperatures fluctuate less than 20 degrees, and 12-hour days provide equal amounts of sunlight and darkness. Tropical rainforests, as opposed to temperate rainforests, always exist in a warm environment. Because of the limited fluctuation in temperature during daylight hours, rainfall remains constant and heavy. Some tropical rainforests get up to 400 inches of rain per year, however the average is 160 inches. The rain falls year-round, because there are no warm and cool seasonal changes to affect rainfall amounts. The Amazon rainforest is the largest, and gets rain 130 to 250 days per year. Humidity stays at a constant 80 percent, and it is rare that rainfall dips below six inches per month

Temperate Rainforests

Temperate rainforests are less common than tropical rainforests. They are found along coastal areas. The largest and most famous temperate rainforest is along the west coast of the United States, north of California and extending up to Alaska. Japan, Norway, New Zealand, Great Britain, Chile and Australia have temperate rainforests, as well. The rainfall and humidity remain high, just as in a tropical rainforest, but the temperature does fluctuate more. The fluctuations are not great, however, and frosts and temperatures over 80 degrees are rare. Rainfall reaches an average of 100 inches annually. Temperate rainforests generally are found at higher elevations. Some of the rainfall amounts come from fog, which can be very heavy in a temperate rainforest.

Significance

The Amazon rainforest receives at least nine feet of rain per year. In comparison, dry regions like Texas get only one foot of rain a year. Washington State, in the Pacific Northwest, has one of heaviest annual rainfall averages -- seven feet -- in the United States. So even our wettest state gets two feet of rain less per year than the Amazon rainforest. Maintaining precipitation and temperature levels across the globe depends in part on maintaining the rainforests. Scientists have found that deforestation adds 20 percent to worldwide greenhouse gas effects. Trees absorb carbon dioxide throughout their lives, only releasing it when they die. The destruction of millions of trees at one time speeds up the carbon release, adding to the earth's greenhouse gas problems. This, in turn, raises the earth's temperature and lowers precipitation levels. The cycle of destruction then continues, as rising temperatures prohibit rainforest biomes from thriving and producing trees that absorb carbon dioxide. Rainforests remain an important global asset that should be protected.

References

• Rainforest data
• Forest classifications and climate
• Conservation site with rainforest information