3.1.1.5 Case Studies Flashcards
The amazon rainforest and the River Exe
Where is the Amazon rainforest?
between the tropics
the majority lies within Brazil with the remainder mainly in Peru and Columbia
How large is the Amazon rainforest?
2.1 million square miles
How much of the Earth’s surface do tropical rainforests cover?
6%
How much of global photosynthesis do rainforest account for?
30-50%
What is the avg annual rainfall in the Amazon?
2000+ mm
What is the avg daily temperature in the Amazon?
27 degrees c
How much of the world’s oxygen do rainforests emit?
28%
what is the climate like in the amazon?
high, daily precipitation as a consequence of low pressure and high humidity conditions
how much precipitation is intercepted by the canopy?
75%
How much of all available rainwater is used by plants and returned to the atmosphere by evapotranspiration?
50%
what happens to the remaining half of all available rainwater?
infiltrates into the soil
why are the trees of the forest critical to the regions water supply?
because evapotranspiration ensures water enters the atmosphere and in turn produces rain
how much rain does the Amazon basin produce through the recycling of evapotranspiration?
1/3
where does the other two thirds of precipitation come form?
in moisture laden air from the Atlantic Ocean
how much of its primary forest has the Amazon lost as a result of deforestation in the last 50 years?
17%
what is the main reason for deforestation of the amazon?
cattle ranching due to huge meat demands
how has deforestation affected evapotranspiration in the amazon? and what effects does this have?
significantly reduced
means the air is less moist resulting in reduction in cloud cover and precipitation
how has deforestation affected interception in the amazon? and what effects does this have?
very little interception now
rainfall can reach the ground immediately which compacts soils. water leaves as overland flow so less is returned to the atmosphere and there is an increase in the risk of flooding
why is more solar radiation reflected by clear land?
it has a higher albedo than forest canopy
what effects of deforestation limits the chances of regrowth?
soil erosion
how will deforestation affect regional rainfall?
decline by 20%
what are rainforests often descried as and why?
lungs of the earth
because they emit a great deal of oxygen
how much carbon does wood/trees store?
50%
how much carbon does the amazon absorb every year?
2.2 billion tonnes of carbon
how much carbon does the amazon emit every year and through what processes?
1.9 billion tonnes
decomposition and organism respiration
how much carbon is stored per square meter in the amazon?
14-40 kg
what is the second largest anthropogenic source of CO2?
deforestation
how much carbon is lost to the atmosphere when forests are cleared and burned?
30-60%
how much has the brazilian amazon rain forest been decreasing each year since 2000?
0.3%
why is the amazon basin no longer a carbon sink?
in 2015, carbon uptake dropped to just 1 billion tonnes
this is less than the total CO2 emitted by Latin America countries each year
why do trees now die sooner in the rainforest?
because changing climate has increased metabolic stress
drought, high temps
where is the river exe?
south west england
rises in the moorland of exmoor and reaches the sea at Exmouth on the south coast of devon
how far does the river exe travel?
83 km
what towns does the river exe pass by?
tiverton and exeter
where is out case study data taken from?
thorverton in the upper area of the catchment
how large in the river Exe catchment?
601 km2
what are characteristics of the Exmoor source of the river?
moorland and peat bogs
used for sheep farmin and shooting game birds
what is the geology of the catchment? and what does it lead to?
impermeable sandstone which leads to a high drainage density
how high is the source of the river exe?
514m ASL
what is the elevation of the river at Thorverton?
26m ASL
what is annual rainfall of the south west of the uk?
1295mm
why does much rainfall form a lot of run off?
impermeable geology
upland peat is already saturated
lots of drainage ditches
describe the regime of the river exe
not very flashy
response to rainfall events occurs relatively slowly
why is the river exe not so flashy?
due to the rural nature of the catchment
how much of the exe catchment is woodland/grassland?
82%
what is a human mitigation strategy that controls the flow of the river so it is not so flashy?
the Wimbleball REsevoir on the River Haddeo which is a tributary of the river Exe
what other human factors affect the regime of the river Exe?
water is abstracted at other locations
agricultural use
why is the River Exe likely to experience more floods in the future?
as climate change makes extreme weather events more likely
when were the last major floods on the river Exe?
1960
how many houses in the Exe catchment at risk of a 1 in 100 year flood?
10%
what does the high risk of floods justify?
the blocking of drainage ditches o Exmoor which attenuates more water in the upper catchment rather than allowing it to enter the river channel
where and how many houses most at rick to flooding in the river catchment?
Exeter - 3-4000 homes
by 2100, how many people will be at risk from flooding in exeter?
4,500
why can’t the peat in the very upper catchment of the River Exe not act as a carbon sink?
it is compacted in saturated conditions and is therefore unable to decompose much due to anaerobic conditions
what method has dried out peat slightly to make it more agriculturally productive?
digging drainage ditches
what is the positive water cycle feedback impacts that digging/ploughing has caused?
means that water can enter the river channel quicker, reducing lag time and increasing the risk of flooding downstream
what impact has drainage ditch digging had on water quality?
there is more Dissolved Organic Carbon (DOC) which makes the water brown
what impacts does DOC have on local water companies?
they have to spend more money on purifying the water and removing the brown colour
as a result of poor water quality and the loss of carbon what move has been made?
blocking up the drainage ditches to restore peat into its saturated state where in sequesters carbon
what problem do landowners have about ditch blocking?
too expensive and they will lose money from agriculutre a their land becomes saturated and boggy again
what is the name of the project that has researched the effects of blocking drainage ditches between 200-2015?
Exmoor Mires Project
what are some key findings of the Exmoor Mires Project?
restoration of peat bogs resulted in a third less water leaving the moorland after heavy rainfall
blocking ditches does reduce carbon transfer but the ditches haven’t been blocked long enough to conclude this
the water table has risen by 2.65cm which provides a significant buffer against downstream flooding
how much has water storage in the peat increased by since drainage blocking?
260,000 cubic metres
