Amazon Rainforest

• The Amazon rainforest is in nine countries and takes up about 6 million kilometers squared, with 70% of it found in Brazil
• Conditions in the tropical rainforest

  • Very high humidity
  • Lots of vegetation
• Rainfall precipitation in the Amazon rainforest

  • Very high average rainfall per year (over 2000 millimeters)
  • No significant dry spell, with variation from 50 to 350 millimeters per month
• Temperatures in the Amazon rainforest

  • Average between 25 and 30 degrees Celsius
  • Little variation across seasons
• Convection rainfall in the Amazon rainforest


  1. Ground heated by intense solar radiation

  2. Heats up air above

  3. Air rises and condenses into clouds

  4. Rainfall occurs
• Evapotranspiration rates in the Amazon rainforest

  Very high, with 60% of rainfall recycled from the biosphere back into the atmosphere
• Vegetation in the Amazon rainforest

  • Dense, with evergreen trees that don't lose their leaves
  • High interception rates, with 20% of rainfall intercepted by trees evaporating back into the atmosphere
• Rainfall and temperature in the Amazon rainforest

  Feedback loop - higher temperatures lead to more rainfall, which leads to more evapotranspiration and rainfall
• Particles released from trees during transpiration

  Help water droplets in clouds to condense
• Water cycle in the Amazon rainforest

  1. Water taken up by tree roots

  2. Transported through stem

  3. Exits through transpiration

  4. Flows through drainage basin to rivers and oceans
• Absolute humidity

  Amount of water that can be stored in a parcel of air, which increases as temperature increases
• Geology of the Amazon basin

  • Crystalline shields (igneous rock) are impermeable, leading to rapid runoff
  • Sedimentary basins (limestone, sandstone) are porous and permeable, allowing infiltration and groundwater flow
• Topography of the Amazon basin

  • Lowlands in most of the basin allow water to infiltrate and flow as groundwater
  • Steeper relief in the west leads to higher surface runoff
• Temperature in the Amazon rainforest

  High temperatures lead to high evapotranspiration, high humidity, and high water vapor in the atmosphere. This then leads to lots of condensation and rainfall.
• Flying rivers

  Atmospheric rivers of water vapor transported by winds across the Amazon basin and South America, containing more water than the Amazon river itself
• High temperatures and heavy rainfall

  Allow good conditions for photosynthesis to occur
• Photosynthesis occurring

  Vegetation grows, carbon moves from atmosphere into biosphere at a rapid rate
• Net primary productivity

  Measure of how much CO2 is taken in by vegetation for photosynthesis and growth, minus CO2 lost through respiration
• Typical net primary productivity figure for tropical rainforest is 2500 grams per square meter per year
• The Amazon rainforest appears green all year round on satellite imagery, due to its evergreen nature
• Evergreen

  Tree cover remains green all year, leaves are not lost in winter like in deciduous forests
• There is rapid cycling of carbon between the atmosphere and biosphere in the tropical rainforest
• High temperatures

  Allow fast photosynthesis and fast decomposition, leading to rapid carbon flows
• Amazon rainforest soils are very infertile, with limited nutrients except in a thin top layer called the humus layer
• Nutrient cycling in rainforest

  1. Trees lose leaves year-round, decomposed quickly by bacteria

  2. Nutrients taken up rapidly by tree roots

  3. Leads to rapid growth of trees
• Heavy rainfall washes out nutrients from lower soil layers
• Amazon rainforest as carbon store

  • 100 billion tons of carbon locked up
  • 2.4 billion tons of CO2 taken in per year
  • 1.7 billion tons of CO2 released per year
  • Net carbon sink
• Carbon storage in rainforest

  • 60% stored in above-ground tree biomass (branches, stems, leaves)
  • 40% stored in below-ground roots
  • 180 tons of carbon per hectare stored above-ground
  • 40 tons of carbon per hectare stored below-ground
• High temperature and rainfall

  Leads to high photosynthesis and high decomposition rates
• Much of the Amazon basin is made up of igneous or metamorphic rock shields that are difficult to weather and have low carbonate content, limiting geological carbon storage
• Limestone outcrops near the Andes mountains are a significant geological carbon store in the Amazon region
• 60% of all carbon is above ground in branches, stems and leaves of trees
• 180 tonnes of carbon per hectare is stored above ground

  40 tonnes is stored below ground
• Amazonia

  • Largest tract of rainforest, dominated by tall evergreen hardwood trees
  • High average annual temperature between 25 to 30 degrees Celsius
  • Small seasonal variation in temperature
  • High average annual rainfall above 2,000 millimeters with no dry season
  • High average temperatures due to intense insulation throughout the year
  • Significant cloud cover ensures maximum temperatures do not reach extremes of subtropical desert climates
  • Seasonal differences in temperature are small
  • Convectional rainfalls all year round though most areas experience at least one drier period
• Water loss from the Amazon basin results in river flow and export of atmospheric vapor to other regions
• This water loss is made good by an influx of moisture from the Atlantic Ocean
• Precipitation in Amazonia

  • High average rainfall above 2,000 millimeters
  • Fairly evenly distributed throughout the year with short drier seasons in some places
  • High intensity convectional rainfall
  • Around 10% of precipitation is intercepted by forest trees
• Interception

  Accounts for about 20-25% of all evaporation
• Evapotranspiration in Amazonia

  • High rates due to high temperatures, abundant moisture and dense vegetation
  • Strong evapotranspiration precipitation feedback loops sustain high rainfall totals
  • Around half of incoming rainfall is returned to the atmosphere by evapotranspiration
  • Most evaporation is from intercepted moisture from leaf surfaces
  • Moisture loss in transpiration is derived from the soil via tree roots
• Runoff in Amazonia

  • Rapid runoff related to high rainfall, intensive rainfall events and well-drained soils
  • Dependent on seasonal distribution of rainfall
  • River discharge may peak at one or two months of the year