Earth’s Life Support Systems SG3
How do the Water and Carbon Cycles Operate in Contrasting Locations?
Tropical Rainforest
An Introduction to Tropical Rainforests
What is a tropical rainforest?
Areas of tropical rainforest climate
No dry season
All months have an average precipitation of at least 60mm
Lowland equatorial evergreen forest
What is the Climate Like in the Amazon Rainforest?
Temperature Rainfall
High average annual temperatures (26 – 27.7 oC) High average annual rainfall of 2289mm
Small seasonal variation in temp No dry season
Only 1.7oC temperature range Wettest in March – 313mm
Driest in August – 60mm
Drier period from June to September
The annual pattern of rainfall in the Amazon Rainforest:
Near the equator, solar heating is intense year round.
The Sun heats the ocean, evaporating large amounts of water.
This daily cycle of heating, evaporation, and convection creates a persistent band of showers and
storms around Earth’s middle.
This tropical rain belt stretches out across the open ocean.
The tropical rain belt migrates north and south of the equator as the seasons change, leading to
pronounced wet and dry seasons in many tropical countries.
What are the Characteristics of the Rainforest Vegetation?
High density “Lungs of our planet”
Continuously recycle CO2 into oxygen 3100 billion trees
1/5 of the planet’s biomass carbon store 15,000 species
Fast growing trees Produces 20% of earth’s oxygen
NPP = 2500gm2yr Layered structure
Only 1% of sunlight reaches forest floor Trees reach 40m high
What are the Characteristics of the Rainforest Soil?
Leaching due to high precipitation
Top 15 – 20cms of the soil is the nutrient rich leaf litter
Very deep due to rapid chemical weathering of the bedrock
The Rainforest Water Cycle
The Amazon River is 4,000 miles long and carries approximately 20% of all water discharged to the Earth’s
oceans
The dense canopy of tropical forests mean rates of interception are high and so rates of
evapotranspiration are high = transfer of latent heat to the atmosphere driving local convectional
rainfall along with high humidity = high rates of precipitation
10% of rain intercepted
, Amazon stores ½ of Earth’s
Output of water water
from Amazon Basin
Input of water from Atlantic
50% of Amazonian rainfall is Ocean into Amazon Basin
recycled in
evapotranspiration – Output of water from the
precipitation feedback loop Amazon Basin
How Does Water Enter the Amazon from the
Atlantic Ocean?
1) Sunlight is intense, so the sun heats the ocean, evaporating large amounts of water
2) Cloud formation occurs
3) Trade winds blow these clouds towards the Amazon Basin where rainfall then happens
Stores of Water in the Amazon Rainforest:
Atmosphere
Clouds/water vapour
Surface water
Biomass
Soil
Absolute Humidity – the mass of water vapour in a given volume of air
Natural Factors Affecting the Water Cycle in the Amazon Rainforest
Factor Effect on the River Discharge (Flood Hydrograph)
27.7oC on average
Temperature consistent – little range (1.7oC)
High temperature means lots of evapotranspiration
High condensation, leading to convectional rainfall
Temperature High precipitation so high interception
High temperature and rainfall increase plant growth so more leaves
to intercept
High precipitation means more saturated soil and more surface
runoff however rain may not reach the ground
Igneous rocks = impermeable
Sedimentary rocks = permeable
Mixture of permeable and impermeable bedrocks in Amazon Region
Geology: Rock Impermeable (in Para) = no percolation so high rates of surface
Permeability and Porosity runoff and overland flow and low underground stores
Permeable = high percolation so less surface runoff and larger
underground stores
Higher flood risk in permeable rock areas
Steeper relief in West Regions
Most of the Amazon has gentle relief so water moves across the
Relief
surface or by throughflow to streams/rivers
Steep relief in West means rapid runoff across floodplains
The Rainforest Carbon Cycle
How do the Water and Carbon Cycles Operate in Contrasting Locations?
Tropical Rainforest
An Introduction to Tropical Rainforests
What is a tropical rainforest?
Areas of tropical rainforest climate
No dry season
All months have an average precipitation of at least 60mm
Lowland equatorial evergreen forest
What is the Climate Like in the Amazon Rainforest?
Temperature Rainfall
High average annual temperatures (26 – 27.7 oC) High average annual rainfall of 2289mm
Small seasonal variation in temp No dry season
Only 1.7oC temperature range Wettest in March – 313mm
Driest in August – 60mm
Drier period from June to September
The annual pattern of rainfall in the Amazon Rainforest:
Near the equator, solar heating is intense year round.
The Sun heats the ocean, evaporating large amounts of water.
This daily cycle of heating, evaporation, and convection creates a persistent band of showers and
storms around Earth’s middle.
This tropical rain belt stretches out across the open ocean.
The tropical rain belt migrates north and south of the equator as the seasons change, leading to
pronounced wet and dry seasons in many tropical countries.
What are the Characteristics of the Rainforest Vegetation?
High density “Lungs of our planet”
Continuously recycle CO2 into oxygen 3100 billion trees
1/5 of the planet’s biomass carbon store 15,000 species
Fast growing trees Produces 20% of earth’s oxygen
NPP = 2500gm2yr Layered structure
Only 1% of sunlight reaches forest floor Trees reach 40m high
What are the Characteristics of the Rainforest Soil?
Leaching due to high precipitation
Top 15 – 20cms of the soil is the nutrient rich leaf litter
Very deep due to rapid chemical weathering of the bedrock
The Rainforest Water Cycle
The Amazon River is 4,000 miles long and carries approximately 20% of all water discharged to the Earth’s
oceans
The dense canopy of tropical forests mean rates of interception are high and so rates of
evapotranspiration are high = transfer of latent heat to the atmosphere driving local convectional
rainfall along with high humidity = high rates of precipitation
10% of rain intercepted
, Amazon stores ½ of Earth’s
Output of water water
from Amazon Basin
Input of water from Atlantic
50% of Amazonian rainfall is Ocean into Amazon Basin
recycled in
evapotranspiration – Output of water from the
precipitation feedback loop Amazon Basin
How Does Water Enter the Amazon from the
Atlantic Ocean?
1) Sunlight is intense, so the sun heats the ocean, evaporating large amounts of water
2) Cloud formation occurs
3) Trade winds blow these clouds towards the Amazon Basin where rainfall then happens
Stores of Water in the Amazon Rainforest:
Atmosphere
Clouds/water vapour
Surface water
Biomass
Soil
Absolute Humidity – the mass of water vapour in a given volume of air
Natural Factors Affecting the Water Cycle in the Amazon Rainforest
Factor Effect on the River Discharge (Flood Hydrograph)
27.7oC on average
Temperature consistent – little range (1.7oC)
High temperature means lots of evapotranspiration
High condensation, leading to convectional rainfall
Temperature High precipitation so high interception
High temperature and rainfall increase plant growth so more leaves
to intercept
High precipitation means more saturated soil and more surface
runoff however rain may not reach the ground
Igneous rocks = impermeable
Sedimentary rocks = permeable
Mixture of permeable and impermeable bedrocks in Amazon Region
Geology: Rock Impermeable (in Para) = no percolation so high rates of surface
Permeability and Porosity runoff and overland flow and low underground stores
Permeable = high percolation so less surface runoff and larger
underground stores
Higher flood risk in permeable rock areas
Steeper relief in West Regions
Most of the Amazon has gentle relief so water moves across the
Relief
surface or by throughflow to streams/rivers
Steep relief in West means rapid runoff across floodplains
The Rainforest Carbon Cycle
