Tropical rainforests are strongly influenced by climate and are situated in the world’s hot and moist zones. The tropical rainforests receive more of the sun’s energy than any other vegetation type on Earth. This means the climate of the rainforest is very hot and very wet. Rainforests possess a constant temperature and heavy rainfall characterizing their climatic zone. They grow in a small range of temperatures but a relatively wide range of precipitation. This combination of climatic factors, among others, creates the unique environment for tropical vegetation.
The temperature of rainforests remains relatively static throughout the year. As an example, in Belem the coldest month is February at 30°C (86°F) and the hottest month is October with a temperature of 32°C (89°C) This consistent temperature is due to the sun being almost straight overhead. This relative position of the sun means there is little change to the amount of daylight throughout the year. The daily temperature change is often greater than that between months and can be up to 17 degrees. The hottest part of the day is from midday to around 3pm in the afternoon. The temperature for this period can approach 35°C (95°F). The hot afternoon is contrasted by cold nights, which get down to around 18°C (64°F).
Tropical rainforests usually have a predictable cycle of temperature and humidity. The morning mists are caused by night-time cooling then, with mid-morning convection, clouds are formed. These are often transformed to storm clouds in late afternoon causing the heavy rains.
Tropical rainforests have a high amount of rain with variation linked to latitude and the Earth’s surface. The coastal areas, islands, and some mountainous regions, such as western Amazonia, have the highest rainfall. Rain often falls in strong showers accounting for around 2,438 mm (96 inches) per year in Belem (a rainforested city in Brazil) and 3,203 mm per year in Cayenne (Capital city of French Guiana) compared to only 561 mm (22 inches) in San Francisco and 595 mm (23 inches) in London.
As well as heavy rain, precipitation can fall in a more gentle and lengthy manner. Many locals in South America refer to the two types of rain as man’s and woman’s rain. True to their name, rainforests have a large number of rainy days. For instance, the rainforest city of Belem in eastern Brazil experiences 243 days of rain per year.
Over the last two million years, climatic changes are thought to have significantly decreased rainforest coverage. However, since 1945, this shrinking has been accelerated by human activity.