Case Study: Amazon Rainforest

Question 1

What is the total annual rainfall of the Amazon?

Answer 1

Over 2,000mm
Rises to 6,000 mm in some NW regions

Question 2

What proportion of the total input of precipitation leaves the Amazon Basin as river discharge into the Atlantic? What happens to the rest?

Answer 2

~ 1/3 discharges into the Atlantic which is below average for a river

Most of the remaining 2/3 leaves the system via évapotranspiration and can fall again as precipitation

Question 3

What is the average temperature in the Amazon and how does this effect water transfers/processes?

Answer 3

27oC all year round (no seasons).

High rates of evaporation transferring water to the atmosphere where can condense, form clouds, and fall as precipitation (daily convectional rainfall).

Question 4

How does the structure of the tropical rainforest effect water transfers/processes?

Answer 4

• The canopy intercepts up to 50% of precipitation.
• Some will be evaporated from leaves the rest reaches the ground as throughfall or stem flow where is taken up by roots and returns to the atmosphere via transpirations.
• Relatively little water enters groundwater stores or runsoff into rivers.

Question 5

Identify the biggest cause of deforestation

Answer 5

Agriculture – commercial crops e.g., soy and palm oil and cattle ranching.
Cattle ranching accounts for 80% of forest lost.

Question 6

How much of the Amazon Forest has already been lost?

Answer 6

17% over the last 50 years (close to 1/5)

Question 7

What proportion of the Amazon Forest will be treeless by 2030 if current rates of deforestation continue?

Answer 7

More than 1⁄4 according to the WWF.

Question 8

How does deforestation or conversion of forest to crops, affect water stores and transfers?

Answer 8

• Vegetation storage reduces.
• Increased river discharge locally. This is due to:
o Fewer trees to absorb water.
o Less interception.
o Reduced infiltration.

• Lower rainfall locally and regionally. This is due to:
o Less evapotranspiration so less condensation, smaller clouds, and less precipitation.
o Studies by Leeds University suggest that regional rainfall could reduce by up to 20%.

Question 9

Give a place example to illustrate the impact of deforestation on the water cycle.

Answer 9

In Rondônia, one of the most heavily deforested areas of Brazil, data shows an 18-day delay in the rainy season compared to the 1970s.

Question 10

There’s evidence that local areas next to cleared forest have experienced an increase in rainfall. Explain.

Answer 10

Air over a cleared area warms faster than air over forest. This creates localised low pressure as the warmer air rises. This results in localised convectional rainfall.

Question 11

Burning is often used to clear felled timber for agriculture. This can reduce rainfall. Explain.

Answer 11

The burning produces ultrafine airborne aerosols (particles). Water condenses around airborne particles, but these are so small that the droplets formed are too small and light to fall as rain.

Question 12

What proportion of all carbon in the biosphere is stored in the Amazon?

Answer 12

1/5 or 20%

Question 13

Untouched Amazon forests act as a major carbon sink. How much carbon does the Amazon Rainforest absorb in a normal year?

Answer 13

2 billion tonnes of

Question 14

What proportion of global photosynthesis do rainforests account for?

Answer 14

30-50%

Question 15

Amazon soils store more carbon than the biomass above. What % of soil carbon is found in the top 30cm of the soil?

Answer 15

52%

Question 16

What Proportion of anthropogenic carbon emissions come from deforestation?

Answer 16

10% (second cause after burning hydrocarbons). Arguably as significant given the role forest play in sequestering carbon.

Question 17

Until the 1990s increases in atmospheric CO2 increased carbon sequestration in the Amazon. Explain why. What type of feedback is this an example of?

Answer 17

The increased concentration of atmospheric carbon led to increased rates of photosynthesis, transferring carbon to the biosphere. This is an example of negative feedback.

Question 18

In the 21st century the Amazon can absorb less carbon. Explain why. Give evidence.

Answer 18

Increased carbon concentrations in the atmosphere caused plants to grow more quickly, however they also die more quickly. In 2015 the Amazon sequestered half the carbon did in the 1990s.

Question 19

How does deforestation or conversion of forest to crops, affect other carbon stores and transfers?

Answer 19

• Less carbon stored in biomass.
- The forest scrub, or crops, that replace tropical rainforest store 40% less carbon. This is due to the lack of nutrients in the soil (no trees so no leaves to decompose to produce humus).
• Less carbon stored in soils.
- Removal of the forest canopy means the sun’s strike the ground directly, drying out soils and lead to less decomposition. Rain also falls on the unprotected soil causing erosion.
- Pastureland (cattleranching) soils contain 9x less carbon than rainforest soils due to a lack of decomposers.

Question 20

Give an example of positive feedback in the Amazon linked to climate change.

Answer 20

• Rising temperatures cause increase in droughts, e.g. in SSE Amazonia > trees lose their leaves > less photosynthesis and transpiration > less rainfall > tallest trees die first > large amounts of carbon released plus lesson photosynthesis and transpiration > increase in carbon emissions > rising temperatures cause increase in droughts…

• Climate change/deforestation cause drier conditions > more wildfires > increased atmospheric aerosols > decrease in droplet size > less precipitation > drier conditions …

Question 21

Give evidence of the positive impact of human activities in the Amazon this century.

Answer 21

Deforestation slowed by 75% between 2000 & 2021. This was due to bans, better governance, and consumer pressure.

Question 22

Give specific examples of recent mitigation strategies that have contributed to a decrease in deforestation.

Answer 22

• Soybean moratorium – exporters, soybean producers, and supermarkets committed to only source products from certified land that hadn’t been deforested since 2006. Effective as it targets whole supply chain. GPS data has enabled effective tracking. Over 99% of soybean crops planted on
certified land.
• Protected areas – an extensive network of protected areas have been established since 2022. They now cover over 50% of the forest, with half reserved for indigenous people who are permitted to use the forest resources. Studies of the protected areas show them to produce ten times less emissions compared to neighbouring areas.
• International support – Since 2007 Norway has pledged $1 billion to Brazil’s Amazon Fund (campaign for zero deforestation). Brazil gets the money only if it can prove a reduction in deforestation. Success can depend on the political leadership, e.g., during President Bolsonaro’s leadership of 2018-19 deforestation rates increased but they are now falling again.