A forest that changes its own weather

The Amazon

The Amazon Basin covers 2,700,000 square miles (7,000,000 square kilometers), making it the largest drainage basin in the world. It occupies more than 40% of South America’s land area, and much of the basin is covered by dense tropical rainforest. NASA JPL The Amazon River runs almost 4,000 miles (about 6,400 km) across northern South America from the Andes to the Atlantic Ocean. NASA It carries twenty percent of all river water discharged into Earth’s oceans, ten times the volume of the Mississippi River. NASA If the Amazon River Basin were draped over the continental United States, NASA says, it would cover more than three fourths of the country. NASA Surrounding the waters of the basin are over 2.7 million square miles (7 million square kilometers) of lush forest. NASA

One of the most important biodiversity hotspots in the world, the Met Office says, is the Amazon basin. Met Office The vast Amazonian system is large enough to modify its own weather and climate, which helps to perpetuate the rainforest and all of its dependent species, industries and communities. Met Office

Located on the equator, Amazonia has a rainy season and a dry season, instead of the four seasons of temperate latitudes. The rainy season starts in the south in December, and gradually moves north through May. NASA The Amazon rainforest experiences seasons, NASA says, but the changes are far more subtle: temperatures and sunlight remain pretty consistent year-round, but rainfall varies cyclically. NASA Though there are regional variations, June through September are generally the driest months, and December through March are the wettest. While it still rains a significant amount all year, precipitation often drops by half from the wettest months to the driest. NASA Each of the two predominant seasons, dry and wet, is approximately six months in duration. NASA JPL The driest month in the Amazon Basin is August, when the average rainfall is approximately 2 inches (5 centimeters). During the wet season, rainfall is greatest from December to May, and can exceed 8 inches (20 centimeters) per month. NASA JPL Over a year, the Amazon Basin averages an extraordinary 6 to 10 feet (1.8 to 3 meters) of rainfall. NASA JPL

For Manaus, Brazil, NASA lists monthly precipitation from 1970-2000 that sums to 2,323 mm for the year, with April the wettest month at 310 mm and August the driest at 68 mm. Monthly average temperatures stay between 27°C and 28°C. NASA

The Amazon Rainforest engages in a perpetual, self-watering cycle by storing and recycling at least one-half — some scientists think perhaps even two-thirds — of the regional rainfall. NASA The forest pumps huge quantities of water into the air through transpiration. That moisture fuels vast "flying rivers" and provides about half of the rain that falls back down on the region. NASA The Amazon rainforest recycles much of the annual rainfall back into the atmosphere, and NASA JPL notes that the release of moisture back to the atmosphere hastens the onset of the wet season. NASA JPL

More than 9 feet (2.7 meters) of rain fall in portions of Amazonia each year, in that NASA wording. NASA In fact, 75 percent of the energy that drives atmospheric circulation comes from the heat released during tropical rainfall. NASA

A NASA Earth Observatory feature dated 31 December 2002, still on the page we checked, says that perhaps as much as one half of all life forms on the planet live in the Amazon River Basin, and later that the region supports perhaps half of all species on the planet. NASA Ten per cent of the world's biodiversity is thought to exist within this region, in the Met Office's 2024 wording. Met Office

While some recent findings indicate the Amazon rainforest may be close to becoming a source of carbon, it has generally functioned as an enormous carbon sink. NASA Tropical rainforests today serve as sinks for more than 50 percent of all atmospheric carbon dioxide absorbed by plants annually, and they exhibit unparalleled biodiversity. Britannica

An analysis of geostationary satellite data found that Amazon forests were slightly greener, about 10 to 15 percent on average, during the dry season, because some trees put out an extra flush of leaves in anticipation of extra sunlight. NASA

That interconnected system faces the threat of effectively drying out, "tipping" this region from lush rainforest to a drier state of degraded forest or even savanna grassland. Met Office Projections have shown that a combination of substantial deforestation in conjunction with climate change could be sufficient to set in train an irreversible path to one of these new states. There is uncertainty about just how quickly this could happen. Met Office The Met Office has been actively involved in research in the Amazon for over 40 years. One current major project is AmazonFACE, funded jointly by the governments of the UK and Brazil, which studies the response of the forest to higher levels of carbon dioxide. Met Office

Forest loss more broadly, as FAO counted it in 2020, is on the life page, labelled as forests, not as rainforest alone.