WC - The Amazon Rainforest - Case Study

Characteristics, human impacts, w+c cycles, attempts to limit impacts

Give some key characteristics of tropical rainforests:

• Annual rainfall of 2000+ mm

• 27 degrees year-round

• Home to ½ of all species on Earth

Describe the characteristics of the water cycle in the tropical rainforest:

• High precipitation due to high humidity

• Convectional rainfall creates regular rainfall patterns

• The canopy intercepts 75%

• 25% evaporates, of the 75% remaining ½ is used by plants and ½ flows into aquifers of rivers

Describe the characteristics of the carbon cycle in the tropical rainforest:

• A lot is stored in foliage

• A fast cycle due to hot, moist conditions encourages growth and decomposition

• Wood is ~50% carbon

Describe the carbon storage of the Amazon rainforest:

• It sinks ~1-3 gTc/year

• It increases by 0.3-0.5%/year

• Higher CO2 levels have driven growth, but also faster life cycles

• It peaked in absorption at 2 gTc/year in the 1990s

Describe flows and stores of water in the Amazon:

• A discharge of 175,000 m³s-1 into the Atlantic Ocean

• This is 15% of freshwater flow in total!

• The Rio Negro, a tributary of the Amazon is the 2nd largest relative to water flow and is 144km wide at it’s mouth in Manaus

• Avg. rainfall of 2300mm a year

• In some areas it can exceed 6000mm a year

Describe historical and current changes in the Amazon rainforest of both cycles:

• Between 2000-7, it was deforested at >19,000 km²/year

• Brazil is the 4th largest polluter - 75% of their emissions are due to deforestation + land use change

• Slash + burn reduces topsoil humidity retention, allows fast evap. and increases albedo and reduces soil porosity

• Clouds from deforested land forms cumulus clouds that rarely rain

• Forests absorb 11% more solar radiation

• Pastures can get 8.9 degrees hotter and vary by 5.2 degrees more

• Deep forest roots evapotranspirate 5-20% more than pastures

Give some key facts about climate change in the Amazon:

• Studies have found a 0.26 degree increase in avg temperatures every 10 years since the 70s

• However rainfall hasn’t fallen significantly since the 70s

Describe the issues with climate change in relation to vegetation:

• Some species can’t adapt fast enough to new conditions

• Droughts may have killed millions of trees

• A 2 degree rise would kill 20-40% in 100 years, 3 75% and 4 85%

Describe the issues with climate change in relation to soil:

• It stores 4-9kg of CO2 per m² (of the top layer) whereas pasture stores only 1kg per m²

• Soil microorganisms die

• Topsoil is easily eroded or washed away

Describe the issues with climate change in relation to rivers:

• Reduction in discharge

• Increase in silt washed out into rivers

• Flooding

• Destruction of freshwater ecosystems and indigenous people’s water supplies

• Reduction in dissolved CO2 levels

Describe some attempts to limit the impacts of climate change on the Amazon:

• Selective logging methods

• Replanting - Peru aims to replace 3.2m ha by 2020

• Bans on excessive logging e.g the Brazilian Forest Code requires 50-80% of land to be kept as forest

• Reserves e.g. Tumucumaque National Park and Para Reserve

• Agreements e.g. TARAPOTO and REDLACH