Rainforest

• Which air cell affects Manaus? What is happening here?

  • The Hadley Cell
• What is happening in the Hadley Cell in Manaus?

  • air is rising due to hot temperatures from insolation being greatest near the equator

  • advection moves it North and South until it becomes cool enough to sink
• What is advection?


  horizontal movement of air
• What is insolation?


  level of solar radiation received by the Earth
• When is there less rainfall in Manaus? Why?

  • between June and October

  • the Earth's tilt moves the Intertropical Convergence Zone (ITCZ) North, away from Manaus, so it's drier
• When is there more rainfall in Manaus? Why?


  • between November and March

  • the Earth's tilt moves the Intertropical Convergence Zone South of the equator, over Manaus
• What is the intertropical convergence zone?


  location of the most intense solar radiation, which powers rapid rising air, so there's intense rainfall
• Evapotranspiration


  • high rates due to high temperatures, lots of moisture and vegetation

  • 1/2 of incoming rainfall is returned to atmosphere via this

  • most evaporation is from intercepted moisture from leaf surfaces

  • moisture lost in transpiration is from soil via plant and tree roots
• Precipitation


  • average annual rainfall= 2000mm

  • rainfall distributed fairly evenly throughout the year

  • formed by convectional rainfall

  • interception by forest trees is high (10% of precipitation)
• Runoff


  • well-drained soils and rainfall lead to rapid runoff, so river discharge may peak in 1 or 2 months of year
• Soil moisture


  • abundant rainfall and deep tropical soils lead to significant water storage in soils and aquifers
• Atmospheric moisture


  • high temperatures allow atmosphere to store lots of moisture- relative humidity is high
• What physical factors affect the water cycle in the Amazon rainforest?


  geology, relief, temperature
• How does geology affect the water cycle?


  • basin made of a mixture of crystalline shields (impermeable) and sedimentary basins (eg. chalk, sandstone, limestone) which are permeable

  • influences percolation and infiltration as well as how much water is available to evaporate
• How does relief affect the water cycle?


  • after leaving the Andes, the elevational gradient of the Amazon is very low

  • the mouth of Rio Negro, where much river runoff occurs has a slope of only about 1cm per km

  • runoff is fairly quick
• How does temperature affect the water cycle?

  • high temperatures drive the rapid convectional rainfall and Hadley cells

  • Cumulonimbus clouds are formed and water droplets fall as rain due to gravity

  • air cools and condenses with height, forming clouds at dew point
• What is net primary productivity?

  2500g /m3/year
• How much is the biomass?

  between 400 and 700 tonnes/ ha
• Why are exchanges of carbon between atmosphere, biosphere and soil so rapid?

  • due to warm, humid conditions

  • ensure speedy decomposition of dead, organic matter and quick release of CO2
• What is evidence for the rapid rate of decomposition?


  such poor soils support biome with highest NPP and biomass
• What are physical factors affecting the water and carbon cycles in the Amazon?

  temperature, rocks, relief, vegetation, soil organic matter
• How does temperature affect water and carbon cycles?

  • average daily temperature= 20-25

  • higher temperatures leads to more water evaporating and warmer air holding more water vapour and more intense rainfall

  • higher temperature means higher rate of photosynthesis

  • higher rates of decomposition as it is ideal for decomposer organisms
• How do rocks affect water and carbon cycle?

  • Amazon rainforest has a mixture of bedrock

  • impermeable catchments have minimal water storage capacity so there's rapid runoff

  • porous and permeable rocks allow lots of rapid percolation and infiltration in soil- there will be less surface runoff, so less water in river storage and more in soil moisture storage and groundwater storage

  • rocks also absorb CO2 gas by binding it with minerals to form solids like calcium carbonate
• How does relief affect carbon and water cycle?


  • most of Amazon Basin is made of low land, but there's steep slopes in the West due to the Andes

  • gentle relief areas- water moves across surface (surface runoff) or horizontally through soil (throughflow) to rivers

  • steep catchments have rapid runoff

  • widespread inundation across extensive floodplains occurs annually, storing water for several months and slowing movement into rivers, reducing lag time
• How does vegetation affect carbon and water cycle?


  • trees dominate biomass and are 60% of carbon store

  • 100billion tonnes of carbon locked in Amazon rainforest

  • drip-tip leaves- allow water to runoff quickly- less interception storage and more throughfall
• How does soil organic matter affect carbon and water cycles?


  • heavy rainfall and warm temperature leads to rapid decomposition of organic matter and weathering of soil minerals

  • high temperature and humidity- rapid decomposition of litter by soil organisms

  • this releases nutrients to soil for immediate take-up by tree root systems and emits CO2 which is returned to atmosphere
• How much does deforestation increase run-off?

  by a factor of 27
• What is happening to the soil?

  It is being washed away due to heavy rainfall
• How much less water is held in the soil?


  15%- faster run-off and silting of rivers
• Rainforests have ... more humidity and ... more rainfall than pasture land

  20-30%, 5-20%
• Deforested regions receive... of rainfall than areas that are forested

  1/2
• What inhibits cloud formation and rainfall?


  • fewer salts and organic fibres are being emitted through transpiration, so there's fewer condensation nuclei

  • trees can't intercept rainfall, extract water from soil or release water vapour through transpiration, so clouds and rainfall aren't formed
• How far away are the effects of deforestation felt?

  100s of km away
• How much is regional rainfall predicted to decline?

  20%
• Impact of deforestation on the carbon cycle in the Amazon
• How does deforestation affect decomposition?

  • decomposition means soils are exposed to more sunlight

  • less decomposer organisms can survive

  • reduced rate of movement of carbon from soil to atmosphere
• How much carbon is lost to the atmosphere in deforestation?

  30-60%
• How much carbon do rainforests absorb per year?

  2.2kg/m2
• How much carbon do grasslands absorb per year?

  0.5kg/m2
• By 2050, Amazon temperatures will have risen by how much? Why?


  • 2-3 degrees

  • forests absorb more solar radiation, cooling the land