Case study: The Amazon Rainforest

What is the area of the Amazon rainforest?

6 million km2

What percentage of rainforest is found in Brazil?

70%

What is the climate in the Amazon?

• Average temps between 25-30 degrees

• Small seasonal variation in temperature

• High average annual rainfall with no dry seasons

Why is the climate in the Amazon like that?

• High average temperatures are a response to intense insolation throughout the year.

• However the significant cloud coverage ensures that maximum temperatures do not reach the extremes of sub-tropical desert climates.

• Seasonal differences in temps are small and convectional rainfalls all year round, through most areas experience at least one drier period

What percentage of precipitation is recycled by evapotranspiration?

50-60%

What are the main ways water leaves the Amazon Basin river?

River flow and export of atmospheric vapour to other regions. This loss is made good by an inward flux of moisture from the Atlantic Ocean.

What is the flow of precipitation like in the Amazon?

Rainfall is fairly evenly distributed throughout the year through short drier season occurs in some places. High intensity, convectional rainfall and also means high rates of interception (10%) - it also 20-25% of intercepted rainfall is evaporation.

What is the flow of evapotranspiration like in the Amazon?

• High rates due to high temperatures, abundant moisture and dense vegetation. Strong evapotranspiration - precipitation feedback loops sustain high rainfall totals.

• Half of incoming rainfall is returned to the atmosphere - most is intercepted by leaves and lost through transpiration from the soil via tree roots

What is the flow of run-off like in the Amazon?

Rapid run-off related to high rainfall, intensive rainfall events and well-drained soil. River discharge may peak in one or two months.

What is the atmospheric store like in the Amazon?

High temperatures allow the atmosphere to store large amounts of moisture (e.g. absolute humidity and relative humidity is high)

What is the soil/groundwater store like in the Amazon?

Abundant rainfall and deep tropical soil lead to significant water storage

What is the vegetation store like in the Amazon?

Rainforest trees play a crucial role in the water cycle, absorbing and storing water from the soil and releasing it through transpiration.

What does the Amazonia’s climate create the ideal conditions for?

• Plant growth

• Net Primary Production is as high of 25000 grams/m2/year

How much carbon does biomass store?

400-700 tonnes/ha

How much carbon does large forest trees store?

1880 tonnes above ground and 40 tonnes in its roots

How much carbon does the soil store?

90-200 tonnes

How much carbon does the Amazon store as a whole?

2.4 bn tonnes a year

What is the consequence of warm, humid conditions?

Rapid exchanges of carbon between the atmosphere, biosphere and soil

What are the Amazon’s soil like?

Its leached and acidic soils support a biome with the highest NPP and the most biodiverse area has poor soil nutrients due to the composition.

The impact of physical factors on the water cycle: Geology

Large parts of the Amazon Basin are compromised of impermeable crystalline - rocks have mineral storage capacity leading to run-off permeable and porous rocks such as limestone and sandstone store rainwater and slow run-off

The impact of physical factors on the water cycle: Relief

Most of the Amazon Basin comprises extensive lowlands in areas of gentle relief, water moves across the surface (overland flow) or throughflow to streams and rivers. Widespread induration across extensive floodplains occurs annually, storing water for several months and slowing its movement into rivers.

The impact of physical factors on the water cycle: Temperature

High temps throughout the year generates high rates of evapotranspiration. Convection is strong, leading to humidity and the creation of thunderstorms - water is frequently cycled continually between the land surface, forest trees and the atmosphere by evaporation, transpiration and precipitation.

The impact of physical factors on the carbon cycle: Trees

• Forest trees dominate the Amazon and 100 bn tonnes of carbon is locked up. It releases 1.7bn tonnes of carbon is locked up through decomposition.

• 60% of carbon is in the biosphere and the rest is in the soil

The impact of physical factors on the carbon cycle: Photosynthesis

NPP averages about 25000 g/m2/year. Amazonia alone accounts 15-20% of all terrestrial ecosystem’s NPP

The impact of physical factors on the carbon cycle: Decomposition

Decomposition releases nutrients to the soil for immediate take up by the tree roots systems and emits CO2 which is returned to the atmosphere.

The impact of physical factors on the carbon cycle: Geology

• The Amazon basin is dominated by ancient igneous and metamorphic rocks that aren’t usually carbonate (not a big sink).

• In the western parts of the basin, close to the Andes, outcrops of limestone occur. In the slow carbon cycle they’re significant regional sinks.

Human factors which impact the water cycle: Deforestation

• The lack of trees has reduced water storage in the forest trees, exposed and eroded soil, permeable rocks (due to more rapid run-off) and in the atmosphere (due to a lack of evapotranspiration) .

• Meanwhile total run-off and the speed if it has increased, raising flood risks throughout the basin

• Converting rainforest into grassland increases run-off by a factor of 27 and half of the precipitation falls directly into rivers.

• Trees are crucial as they extract moisture from the soil, intercept rainfall and stabilise forest albedo and ground temps - this cycle sustain high atmospheric humidity, which is responsible for cloud formation and the patterns of conventical rainforest - deforestation breaks this cycle

Since 1970 how much of the rainforest has been destroyed?

1/5 of the primary rainforest has been destroyed

What occurred during the 2014 Madeira River floods?

Devasting floods in Port Velho where the rover reached record levels of 19.68 m above normal - vast expanses of floodplain were inundated, 60 people died 68,000 were evacuated and there were outbreaks of cholera.

What do projections say about the decline in rainforest?

20% decline in rainforest cover

Human factors which impact the carbon cycle: Deforestation

• Deforestation exhausts the carbon biomass store - it reduces the inputs of organic material to the soil due to its exposure and thus erosion

• It destroys the main nutrient store and removes it as its not taken up by trees but now washed out of the soils due to its lack of protection cover of trees

How much does the Brazilian government want to restore the rainforest?

20,000 km2 by 2030

What has the Brazil govt established since 1998?

Conservation areas (Amazon Regional Protected Areas)

How much of the rainforest is protected as national parks and reserves?

44%

What is the Parica project in Rondonia in the western rainforest?

• NGOs, businesses and local authorities have supported reforestation programmes - they’ve planted 20 million fast growing trees that will be harvest for commercial timber instead of logging mature trees.

• Although this project is monoculture and cannot replicate the biodiversity, it is sustainable and sequesters carbon from the soil.

• The indigenous Surui community plant seedlings in deforested areas which provides them with timber, crops and a sustainable source of income. They joined the UN reducing Emissions from Deforestation and Degradation (REDD) scheme. This included carbon credits which can be purchased by international companies who have exceeded their carbon limit.

• In 2023, Natura (a TNC) purchased 120,000 tonnes of carbon credit from the Surui people

What is the main cause of deforestation?

Farming

What is the impact of farming on the rainforest soil?

• Low fertile soils meant that permanent cultivation proved unsustainable

• After a few years smallholders abandon their land which were low quality grassland. Extensive ranching companies are struggling.

What is diversification?

Soil fertility can be maintained by rotational cropping and combing livestock and arable operations. Integrating crops and livestock could allow a fivefold increase in ranching productivity and help slow down rates of deforestation.

What dark soils?

This is made up of charcoal, waste and human manure and is added to retain soil fertility as it attracts microorganisms - this would allow intensive and permanent cultivation which would drastically reduce deforestation and carbon emissions