CASE STUDIES Flashcards
CASE STUDY: BRAZIL
When was the Brazil drought?
2014-2015
CASE STUDY: BRAZIL physical causes -
In a normal year, where does the precipitation come from in the Amazon basin?
The South Atlantic
CASE STUDY: BRAZIL physical causes -
What diverted rain-bearing winds during the 2014-15 drought?
A series of high pressure systems diverted rain-bearing winds further north.
CASE STUDY: BRAZIL physical causes -
What was the result for Brazil?
Dry air remained over Brazil.
CASE STUDY: BRAZIL physical causes -
What was the result of diverted rain-bearing winds for Bolivia and Paraguay?
Heavy rains
CASE STUDY: BRAZIL human causes -
In Sao Paulo, what did industries, domestic users and farmers increasingly have to use?
Groundwater, as rivers ran low.
CASE STUDY: BRAZIL human causes -
Why were so many people digging illegal wells?
Groundwater became the only water source for the urban poor and for remote rural areas. The govt began to charge high fees for granting a license to drill a well.
CASE STUDY: BRAZIL human causes -
How much did the Brazilian government charge for granting a license to drill a well?
$3000
CASE STUDY: BRAZIL human causes -
What were the problems of digging illegal wells?
They were not monitored for water safety. Illegal wells are generally shallower and less filtered by bedrock so contain industrial pollutants and higher levels of bacteria.
CASE STUDY: BRAZIL human impacts -
What impact did this drought have for people in Brazil?
- street protests
- water rationing for 4 million people, water supplies cut off for three days a week in some towns
- halting of HEP production leading to power cuts
- depletion of Brazil’s 17 largest reservoirs to dangerous low levels
- reduced crop of Arabica coffee beans, which pushed up global coffee prices by 50%
CASE STUDY: BRAZIL physical impacts-
What impact did this drought have for the environment in Brazil?
increased groundwater abstraction, leading to aquifers becoming dangerously low
CASE STUDY:
What is the “flying river” in the sky?
Rain-bearing winds that come from the South Atlantic. Takes up 20 billion tonnes of water vapour from the forest and releases it as rain on central and southern Brazil.
CASE STUDY:
Why is the Amazon referred to as the Earth’s Lungs?
It absorbs CO2 and returns oxygen to the atmosphere.
CASE STUDY:
What are the chain reactions caused by the drought that leads to forest stress?
Younger trees die which reduces the canopy cover. Shorter trees and thinner canopies. This is turn, reduces humidity, water vapour and therefore rainfall.
CASE STUDY: Scientists have suggested the Amazon has reached a tipping point - what do they mean by this?
Changing hydrological and climatic cycles permanently.
CASE STUDY: How is the positive feedback loop of deforestation effecting the forest?
Reducing the ability of the rainforest to regenerate. Fragile rainforest ecosystems are less resilient. Thinning forests have reduced soil water storage.
CASE STUDY: What three factors combined are causing more extreme weather that it likely to lead to more frequent droughts in the Amazon?
Global climate change, ENSO cycles and deforestation.
CASE STUDY: What could drought mean for the Amazon?
- its capacity to absorb carbon will decline
- regional water cycles will change and soil temperatures will increase
- could be replaced with Savannah like grasslands
- more wildfires will increase carbon in the atmosphere
- reduced rainfall will threaten Brazil’s dependency on HEP (which generates 70% of its energy)
- world will lose a major carbon sink and source of moisture
CASE STUDY: Impacts of drought on wetland ecosystems:
What happens to the Pantanal region during the seasonal rainfall floods?
The Pantanal changes from terrestrial into aquatic habitats.
CASE STUDY: Why is the rainy season in the Pantanal region so important?
Aquatic and birdlife depend on it for survival.
CASE STUDY: What impacts did the 2014-2015 drought have on the Pantanal?
- increased tree mortality which reduced habitats for wild animals
- reduced cattle ranching and ecotourism
- wildfires became a major threat which spread quickly
CASE STUDY: What is the Pantanal region?
Large wetland area in central South America within Brazil.
CASE STUDY: When was the Millennium Drought in south-eastern Australia?
1997-2009
CASE STUDY: The Millennium Drought -
What?
Longest uninterrupted series of years with below median rainfall in south-eastern Australia, with annual rainfall 12.4% below the 20th century mean.
CASE STUDY: The Millennium Drought -
Why?
A result of physical and human causes. El Niño prevailing conditions explained about two-thirds of the rainfall deficit in eastern Australia.
Strengthening of high-pressure belt, the subtropical ridge (STR) blocked storm tracks (depressions), forcing them towards higher latitudes and thereby reducing frontal rainfall.
Changes to the Hadley Cell and the STR associated with anthropogenic global warming; in particular, the STR appears to have intensified as global surface temperatures increased, blocking storm tracks.
CASE STUDY: The Millennium Drought
What has anthropogenic warming done to the temperature gradient, resulting in drought?
It is thought that anthropogenic warming is reducing the temperature gradient between the Equator and the Pole, which would reduce the energy available for mid-latitude storm systems and the polar front jet stream. So less rainfall.
However this is an ongoing investigation, and sufficient evidence is yet to be collected to prove this relationship.
CASE STUDY: The Millennium Drought -
Impact?
Reduced rainfall - reduced crop yield, increase of wildfires.
CASE STUDY: The Aral Sea
What countries surround the Aral Sea?
Uzbekistan and Kazakhstan
CASE STUDY: The Aral Sea
What caused the Aral Sea to disappear?
The water supply from two rivers, the Amu Darya and Syr Darya, which carry snow melt from mountainous areas, was diverted by the Soviet Union for irrigation to produce cotton. This eliminated any river inflow to the Aral Sea causing it to disappear.
CASE STUDY: The Aral Sea
By 2007, the Aral Sea shrank to what percentage of its original size?
Shrank 10% of its original size
CASE STUDY: The Aral Sea
Before 1965, the Aral Sea received how much fresh water from rivers? By the 1980s how much did it receive?
2060km³.
By 1980s it received no freshwater.
CASE STUDY: The Aral Sea
Environmental impact?
24 fish species extinct (could not adapt to more saline waters)
Wetlands of the two river deltas have disappeared
Regional climate is drier and has greater temperature extremes due to the absence of moisture and moderating influence from the lake
Southern part of the Aral Sea has seen no relief and remains nearly completely dry
CASE STUDY: The Aral Sea
Social impacts?
Once thriving fishing industry removed
Current shoreline is tens of kilometres from former fishing towns and commercial ports
Rive diversion project meant that many of the irrigation canals were poorly built, allowing abundant water to leak or evaporate
Increasing number of dust storms, blowing salt, pesticides, and herbicides into nearby towns causing respiratory illnesses including tuberculosis
Another example of a lake that has disappeared for human reasons like Aral Sea?
Lake Chad in Africa
What are Lake Chad and Aral Sea examples of?
Large lakes destroyed by unsustainable diversions of river water.
Examples of lakes that have shrunk significantly due to human diversions of water?
Dead Sea - Middle East
Lake Manchar - Pakinstan
Owens Lake - California
Mono Lake - California
What prevents the ITCZ moving north bringing the usual rain to the Sahel region resulting in drought?
High pressure blocks the arrival of the wet season.
Where is the Sahel located?
Africa, at the southern edge of the Sahara desert. Covers parts of 11 countries.
When was the most severe drought in the Sahel?
2011-12
What are the causes of drought in the Sahel?
Possible reasons:
Air pollution generated in Europe and North America. These pollutants are thought to have caused atmospheric cooling, so that tropical rains associated with the ITCZ did not arrive, causing drought.
As a results of higher sea-surface temperatures caused by atmospheric climate warming. Rain-bearing winds that move over the Sahel appear to fail when the sea-surface temperatures in the tropical Atlantic Ocean are warmer than average.
El Niño would increase water stress. Cooler waters in the North Atlantic added to the drying conditions with reduced evaporation.
Where does the Sahel get its water from?
Strong south-westerly rain-bearing winds.
In Sahel drought years, what’s happening with the ITCZ?
The ITCZ doesn’t move as far north as it should, due to high pressure in the north preventing the south-westerly winds bringing the usual rain.
Anticylone - blocks out potential of ITCZ migrating further north.
What causes desertification in the Sahel?
Demand for food and fuel wood is accelerating. Natural dryland ecosystems are progressively being converted into farmland which is being overcultivated and overgrazed. Causes desertification.
Sahel - where the effects of reduced rainfall and human pressures are combined, what happens?
Reduced vegetation cover and soil moisture, could create self-perpetuating droughts.
What is the relationship between desertification and drought in the Sahel?
Desertification increases human vulnerability to the drought hazard.
CASE STUDY: Storm Desmond
What?
December 2015 - storm that brought severe gales and heavy rains to the UK, Cumbria was the worst hit county - a months worth of rain fell in one day (350mm in some places).
CASE STUDY: Storm Desmond
What did it lead to?
Localised flooding in north-west England, southern Scotland, north Wales, and parts of Northern Ireland.
CASE STUDY: Storm Desmond
Why?
Very low air pressure and its fronts brought exceptionally prolonged and heavy rainfall as the air was forced to rise across the high ground of the Lake District.
Convectional and orographic precipitation was combined and, together with already saturated ground, created conditions for extreme flooding. Existing flood defences unable to deal with water levels.
Examples of snowmelt causing flooding
Red River in North Dakota, USA
Norfolk 2013
Cumbria (Storm Desmond)
What?
The Cumbrian fells created orographic rainfall (occurs in areas where land increases height). The moist air mass stayed over Cumbria for up to 48hrs - delivering record amounts of rain.
CASE STUDY: 2007 Flooding in England and Wales
When?
June and July 2007
CASE STUDY: 2007 Flooding in England and Wales
Causes?
High-altitude westerly jet stream stayed south of Britain instead of making its seasonal shift northwards. Heavy rain followed.
Also due to a low pressure system located over Calais in the morning which slowly moved northwest bringing warm, continental air. This, when meeting the cooler air to the North, created an area of instability ideal for storm generation.
Soils were already saturated due to the heavy rainfall occurring in the months leading up to the flooding. This meant water could not infiltrate into the ground, causing overland flow and intensifying the floods.
CASE STUDY: 2007 Flooding in England and Wales
Where in the UK was rainfall most above the 1971-2000 average?
South-west England and South Wales
CASE STUDY: 2007 Flooding in England and Wales
Environmental impacts?
- lakes were contaminated with drain refuse and sewage
- runoff from torrential rain meant that the Ea Beck burst its banks, sending torrents of water and debris into Toll Bar and Bentley
- green spaces flooded and ground saturated
CASE STUDY: 2007 Flooding in England and Wales
Social impacts?
- national death toll reached 7
- 27,000 homes were damaged
- 5,000 businesses had to be evacuated
- in Hull 30,000 people had to leave their homes at the height of the crisis
- major roads were closed like the M1
- residents in 120 flats in Lincoln were evacuated
CASE STUDY: 2007 Flooding in England and Wales
Economic impacts?
- total bill to insurers is put at around $3.3 billion
- overall government support for the flood hit regions is $46 million
- rising interest rates
- the Environment Minister pledged to boost spending on flood defences by £200 million a year by 2011
CASE STUDY: Impacts of drought on forest ecosystems
When did a combination of severe drought and unusually high temperatures lead to a significant die-off of Piñon pines?
Between 2000 and 2003
Where is Piñon pines?
South-west USA, New Mexico
Piñon pines
What?
Hot dry conditions made the Piñons more susceptible to pine bark beetle attacks.
In some areas, what percentage of the Piñons died?
90%
Saltwater encroachment
In the Pacific Islands, small and low-lying.
What do many of the small low-lying Pacific Islands depend on?
Small aquifers for their freshwater supply.
What are the aquifers in the Pacific Islands increasingly threatened by?
Saltwater intrusion, as a result of over-abstraction, climate variability and sea-level rise. Population growth has increased water demand, resulting in an increase in groundwater pumping and a consequent lowering of the water table.
Why is saltwater intrusion (encroachment) a serious threat in the Pacific Islands?
Crop production depends on freshwater irrigation, making saltwater intrusion a serious threat to health, food security and livelihoods.
Where is Karachi?
Southern Pakistan
What’s the problem with Karachi and water?
90% of Karachi do not have access to legal piped water
Global cost of water
Water theft, illegal water hydrants, corrupt water board
Climate change means there’s less rain
Agriculture suffering
Piped water can be dirty/sewage
However some areas, e.g “The Fence”, are rich. Some pat 4,000 rupees for a tank of water every 3 days
Link to urbanisation - cities cannot meed the population’s demand for water.
Where are groundwater levels declining?
In several of the world’s intensive farming areas such as the 𝗡𝗼𝗿𝘁𝗵 𝗖𝗵𝗶𝗻𝗮 𝗣𝗹𝗮𝗶𝗻, and around numerous megacities such as 𝗕𝗲𝗶𝗷𝗶𝗻𝗴.
In 2015, how much contaminated water was released by the US Environmental Protection Agency into the Animas River in Colorado?
1.35 million m³ of contaminated water.
1.35 million m³ of contaminated water was released by the US Environmental Protection Agency into the Animas River in Colorado - where was the contaminated water from?
Mining operations and contained arsenic at 300 times normal levels, and lead at 3,500 times normal levels.
Contaminated water into Animas River in Colorado - what were the impacts?
People and livestock downstream were at risk and access to the river was closed; people with wells were told not to use the water without testing.
Contaminated water into Animas River in Colorado - what was declared?
A local state of emergency was declared by the Navajo Nation Commission on Emergency Management.
Contaminated water into Animas River in Colorado - what happened with the EPA (Environmental Protection Agency) as a result?
Faced widespread criticism.
* Suspended other clean up operations to allow the EPA time to develop emergency plans in case similar accidental pollution occurred.
* EPA opened a temporary water treatment plant at the Animas River mine, a cost of US$1.8 million, to treat the polluted water.
CASE STUDY: Denmark increasing price of water
What has Denmark done in an attempt to reduce unnecessary water consumption?
The government in Denmark decided to raise water prices.
What did Denmark do 20 years ago?
More than 20 years ago, regulation requiring certified metering of all water consumption was set up in Denmark, introducing tax on both water consumed and water supplied, as well as on Non-Revenue Water.
Why has Denmark increased water prices?
High price deters unnecessary consumption.
As a result of higher prices, what has happened between 1989 and 2012 in Denmark?
From 1989 to 2012, the price of water for customers in Denmark has risen from around €2 to €7 euros per cubic metre.
What does the high price of water in Denmark cover?
The increased price is aimed at covering the supply of water (22%), sewage and wastewater treatment (47%), and taxes (31%).
What has the dramatic increase in water price in Denmark resulted in?
Increased public awareness about saving money. There has thus been a significant drop in water consumption in Denmark from a per capita average of 170 litres per day in 1989 to 114 litres per day in 2012.
In Denmark, how has the water consumption changed from 1989 to 2012?
1989: per capita consumption was 170 litres per day
2012: per capita consumption was 114 litres per day
What did the European Union approve in 2000?
The Water Framework Directive, which set out requirements for national water pricing policies. It’s goal was to provide adequate incentives for efficient water usage as well as to incorporate a user contribution to the cost of providing appropriate water services.
What has big incentives to reduce Non-Revenue Water Danish water utilities resulted in?
An incentive to reduce water losses because the amount of water supplied was taxed.
2014 - What did water utilities in Denmark pay in taxes even on their non-revenue water?
Almost one euro per cubic metre.
What else do the Danish authorities do to further encourage water suppliers to reduce water losses?
- Impose additional penalties on water utilities that to not reduced Non-Revenue Water to less than 10%.
- Created a strong incentive for water utilities to reduce urban water loss and to plan, manage and operate the utilities efficiently to the benefit of both the consumers and the environment.
What’s an example of a degraded ecosystems which may have difficulty regulating and restoring itself and has lost resilience?
The Salton Sea in the dry south-eastern part of California.
What does the Salton Sea have?
A productive ecosystem, with fish in its waters and invertebrates in its muds, providing a food source for over 400 species of birds, including pelicans and egrets.
Millions of birds use the Sea as a stopping point when migrating along the Pacific Flyway.
What has been happening to the Salton Sea since 2005?
Water levels have been falling as evaporation from its shallow waters (15 metres deep) exceeds inflow, causing salinity levels to increase (over 50 g/l).
As well as salinity levels increasing, what else is causing the degradation of the Salton Sea?
- Water is in great demand in southern and central California, so water that should reach the Salton Sea is diverted to agriculture, and some inflow consists of contaminated runoff from the fields.
- The Salton Sea is also affected by regional water agreements, and from 2017 to 2018, there could be an 18% decline of inflow, as water will no longer be diverted to it from the Imperial Irrigation District, causing the Sea to shrink by up to 260km².
So what three things are causing the Salton Sea to be degraded?
- Water levels have been falling as evaporation from its shallow waters exceeds inflow, which increases salinity levels.
- Water that has been diverted to agriculture has resulted in contaminated inflow to the Salton Sea.
- Regional water agreements have resulted in diversions, causing the Sea to shrink by up to 260km².
Example of an area where fossil water in aquifers may be extracted
Sahara Desert - an arid region in which fossil water in aquifers may be extracted for human purposes (agriculture, industry and consumption), but there is little to no significant recharge, effectively making this type of groundwater a non-renewable resource.
Where is the highest average annual rainfall recorded?
Mawsynram in India, with 11,873mm of rain per year, mostly during the monsoon season between June and September. High precipitation input into drainage basins.
Where are the lowest precipitation inputs found?
In stable areas of high atmospheric pressure, such as Quillagua in the Atacama Desert, Chile which is the driest place on Earth, receiving less than 0.2mm of rain per year.
How much rain does Mawsynram in India receive every year?
Average 11,000mm of rain per year.
How much rain does Quillagua in the Atacama desert receive each year?
Less than 0.2mm - it is the driest place on Earth.
Continental interiors examples
Gobi Desert in Asia and Alice Springs region in Australia are continental interiors, meaning they are far from the moisture of maritime air masses, so are examples of areas with very little rainfall.
Example of how human activities can disrupt a drainage basin cycle
Amazonia
How is the tropical rainforest in Amazonia, South America, a self-sustaining cycle?
The dense and multiple canopies of vegetation meant that rates of interception and evapotranspiration are high. This causes high humidity and heavy local convectional rainfall and is an example of a self-sustaining cycle as water is effectively recycled within the tropical forest system.
Why is evaporation from the Amazonia rainforest important in sustaining regional rainfall in areas around the periphery of the tropical rainforest?
Because this is important to key agricultural regions of Brazil and other countries.
How is human disruption affecting the Amazon basin?
Deforestation may be significantly reducing evapotranspiration and precipitation, while also increasing runoff and river discharge. E.g the Tocantins River in Brazil showed a 25% increase in river discharge between 1960 and 1997, coincident with increased deforestation.
Deforestation has also resulted in a lowering of humidities and more soil erosion and silt being fed into rivers.
Stat about the Tocantins River in Brazil
The river showed a 25% increase in river discharge between 1960 and 1997, coincident with increased deforestation.
Case study for cloud seeding (human disruptions to the drainage basin hydrological cycle)
- China used cloud seeding in Beijing just before the 2008 Olympic Gamed to create rain to clear the air of pollution.
- Used in the Alpine Meadows ski area in California to improve snow cover.
- Used in Texas 2015 to reduce the impact of drought.
Case study for urbanisation disrupting the drainage basin hydrological cycle and increasing flood risk
Winchester and Maidenhead (2014 floods) and Carlisle, York and Manchester (2015 floods).
Urbanisation has therefore increased flood risk
Case study for dam construction disrupting the drainage basin hydrological cycle and increasing flood risk
Lake Nasser behind the Aswan Dam in Egypt is estimated to have evaporation losses of 10-16 billion cubic metres every year. This represents a loss of 20-30% of the Egyptian water volume from the River Nile.
Case study for groundwater abstraction disrupting the drainage basin hydrological cycle and increasing flood risk
China - groundwater extraction is increasing by about 2.5 billion cubic metres per year, and consequently groundwater levels in the arid North China Plain dropped by as much as a metre a year between 1974 and 2000.
Groundwater is used to irrigate more than 40% of China’s farmland and provides about 70% of the drinking water in the dry northern and north-western regions.
Where has groundwater rebound occurred?
In some of the UK’s major conurbations, including London, Birmingham, Nottingham and Liverpool, as a result of reduced abstraction for industry.
Which river regime is affected by the wet and dry seasons and snowmelt from the Andes?
The Amazon - its peak discharge is in April - May and lowest discharge in September which is linked to wet and dry seasons.
Which river regime is affected by melting snow and ice?
The Yukon River - its peak discharge is in May-June with a dramatic increase due to melting snow and ice, it is low from December-May due to low precipitation and frozen conditions.
Which river regime has been significantly changed by the construction of Aswan Dam in 1970?
The River Nile - the flow below the dam was reduced by 65% and became regulated between seasons so that the flood peaks in September were reduced.
Impact of the Akosombo Dam Lake Volta in Ghana
+ Akosombo is a rockfill dam. A rockfill dam is a structure built mainly of compacted rock and shaped like an embankment or hill.
+ The Akosombo Dam was politically important and it was seen as proof of Ghana’s ability to build major infrastructure projects.
+ Originally, the project supplied Ghana’s aluminium industry with the power it needed. Today the scheme provides 85% of the country’s electricity.
- The Volta Lake is now a habitat for disease-carrying insects such as black flies and mosquitoes.
- People from 700 different villages – many of whom were subsistence farmers - were moved into 52 resettlement villages as part of the scheme.
Difference between the River Kent and River Lambourn (Berkshire)
River Kent made up of impermeable igneous rock in the north and permeable limestone in the south. Mean discharge is 8.89 cumecs.
River Lambourn made up of porous chalk. Mean discharge is 1.69 cumecs.
What part of the UK receives the most rain?
WEST because the western hills force moist air to rise as it approaches from the Atlantic - as it rises, it cools over high ground - producing heavy rain over western and northern parts of the UK.
Specifically, the Scottish Highlands have highest rainfall because it has the highest relief, so more warm, moist air is forced to rise and condense.
How much water does Kenya’s Lotikipi aquifer contain?
An estimated 200 billion cubic metres of freshwater which is 70 years supply at Kenya’s current rate of use, even without the natural replenishment it receives from mountain streams.
Where is Kenya’s Lotikipi aquifer?
The arid Turkana region of northern Kenya.
Why is Kenya’s Lotikipi aquifer important?
- Brings hope to the drought-hit region
- Another aquifer was found in Namibia-sub-saharan Africa and poor parts of Kenya but was hit by drought recently.
At a latitude of 0 (equator), what type of water balance is there?
Positive water balance - more precipitation e.g more rainforests.
At the water balance at the two tropic lines (23.5N/S), what type of water balance is there?
Negative water balance - deserts.
Example of river regimes
River Thames, Alpine Rhone, River Volta, Streams of Sicily, River Congo, River Yenisei
Example of river regimes
River Thames, Alpine Rhone, River Volta, Streams of Sicily, River Congo, River Yenisei
What do Storm Desmond do re waterfalls?
Caused Malham Cove (in the Pennines of North Yorkshire) to become a waterfall for the first time in centuries, because Malham Cove is a limestone area, and limestone is a permeable rock so water usually flows through.
Storm Desmond in 2015 saturated the limestone.
Why can heavy rainfall lead to flooding e.g in Cumbria 2015?
Surface soils become saturated which reduces the ability of the landscape to absorb the excess water.
What is the wettest county in England?
Cumbria - its annual rainfall is over 2000mm.
Within that, places such as Borrowdale receive up to 3,300mm a year.
Example of water store depleting
The ice in the Polar regions and in mountain glaciers is melting without being replenished.
Compare polar and tropical rainforest hydrology
Polar:
- Winter snow insulates the ground and 85% of solar radiation is reflected
- Permafrost creates impermeable surfaces
- Limited vegetation cover reduces heat absorption
- Annual precipitation is less than 200mm
Tropical rainforest
- Dense vegetation intercepts and consumes up to 75% of precipitation
- 50-75% of precipitation then returns by evapotranspiration.
- Evapotranspiration cools the air as energy is used during the process
- Annual precipitation is over 2000mm
Summarise how tropical rainforest hydrology works
Dense forest produces high rates of evapotranspiration, with water returning to the surface as precipitation that feeds large rivers such as the Amazon.
Which stores have the longest residence time? (average length of time that water reminds in each store within hydrological cycle)
Oceans and groundwater
What is the yearly flux of oceans and the atmosphere?
Evaporation 400,000km³ per year
Precipitation 370,000km³ per year
Oceans therefore lose more water through evaporation than they gain through precipitation. The opposite is true for landmasses, who gain more through precipitation. This is because the cycle makes sure the oceans receive less water so the continents are not dry.
Where can aquifers be found?
Beneath Greenland’s ice sheet and under the Kenyan desert.
Where can untapped ancient stores of freshwater be found?
In the polar regions and beneath many deserts.
Comparison of two different drainage basins
The Mississippi basin drains nearly 3.3 million km², much of it remote, while the Thames basin drains 16,000 km², and is very densely populated.
What area of the UK is exposed to air masses approaching from the Atlantic and is prone to orographic and frontal rainfall?
Western side of the UK
What is Cumbria prone to?
Saturated surfaces, high water tables and antecedent moisture - all of which make flooding more likely.
Which area of the UK experiences dry weather but heavy bursts of rain in summer due to convectional air instability?
East Anglia
Example of a drainage basin that is under pressure from growing water demands and greater abstraction
The Thames Basin - home to 13 million, and averages just 690mm of rainfall a year.
Why is the Thames Basin under pressure from over abstraction?
Over 40% of London’s water comes from chalk aquifers. These are replenished by rain falling on the Marlborough Downs to the west of London, the Chilterns to the north, and the North Downs to the South. Abstracting too much water from groundwater reserves leads to rivers drying up in times of low rainfall.
What human activities can disrupt the drainage basin cycle in the Tropics, by accelerating natural processes?
Clearing of forests for new roads and palm oil plantations, and modern agribusinesses.
What impacts can man-made reservoirs have?
- In the Tropics, mats of floating plants on the reservoir’s surface make evapotranspiration six times higher than in open water.
- Salinity levels within the reservoir can also rise as its water evaporates.
- Dams reduce the river flow below them, leading to the loss of vegetation e.g Kenya’s Tana River floodplain forest is dying because dams built upstream have now eliminated floods there.
- Reservoirs abstract water from the drainage basin.
Example of a floodplain forest dying due to constriction of dams
Kenya’s Tana River floodplain forest is dying because dams built upstream have now eliminated floods there.
When does rainfall exceed evaporation in the UK?
From October. Storage areas are recharged by that point, and are usually full by January.
When does potential evapotranspiration exceed precipitation in the UK?
In summer
Example of two places receiving very similar annual rainfall, but with very different rainfall effectiveness?
Effective rainfall is the amount of precipitation remaining after evaporation.
Great Wakering in Essex and Coronado Memorial Park in Arizona, USA, receive similar annual rainfall, but the higher temperatures in Arizona means the rainfall effectiveness is lower and less rainfall remains.
Rainfall in Essex is spread throughout the year, whereas Coronado in Arizona has short intensive bursts separated by periods of drought.
Example of a simple river regime, where rivers rise in mountainous regions where summer snowmelt occurs
The Rhône at Gletsch
Arve at Chamonix
The rivers respond to localised factors within southern France and Switzerland.
Example of complex river regimes, where rivers cross different relief and climatic zones and experience the effects of different seasonal climatic effects
- Mississippi River
- Ganges
- Amazon River
- The Yukon River, Alaska
- Murray-Darling, Australia
- Indus River, Pakistan
Major influences on the Yukon River, Alaska, USA
Tundra, taiga and mountain climates.
Higher summer temperatures, rainfall and snowmelt coincide.
Some HEP for mining industries.
High flow is in spring and summer, caused by melting snowmelt
Major influences on the Amazon, Brazil
Rainforest climate
Seasonal precipitation - rainfall in every month
Evapotranspiration levels very high
Human influences are increasing; large dams used by Brazil’s major cities for irrigation and HEP.
Major influences on the Murray-Darling, Australia
Seasonal sub-tropical climate - monsoon climate in northern tributaries of Queensland, which feeds the Darling; temperate climate in the south, which feeds the Murray.
Most of the basin lies in a rain shadow and undergoes long periods of drought.
Its waters are drawn by Australia’s major cities and farms for irrigation.
Within the UK, who decides whether any proposed development will influence flood risk with the change in land use?
Planners - within England, the National Planning Policy Framework (NPPF) sets out strict guidelines.
What has recently been introduced to reduce runoff (flooding) produced from rainfall?
Sustainable Drainage Systems (SuDS)
Examples of Sustainable Drainage Systems (SuDS)
- green roofs - vegetation cover planted over a waterproof membrane e.g on Adnam’s Brewery distribution centre in Southwold, Suffolk
- infiltration basins - shallow depressions dug out to delay runoff and increase infiltration
- permeable pavements - to delay runoff by using gaps between pavement slabs
- rainwater harvesting - collecting rainwater from roofs to be recycled e.g for irrigating gardens
- soak-away - a channel dug out to disperse surface water into the ground.
- filter drains - trenches filled with gravel to take runoff away
- detention basins - to deal storm runoff for a few hours
- wetlands - retention areas with marsh/wetland vegetation.
How is Singapore tackling water scarcity?
Singapore has invested in research and technology to create a diversified water supply, comprising local catchment water, imported water and desalinated water.
Example of sustainable water management schemes in Singapore
- Local catchment water involves collecting rainwater through a network of drains, canals, rivers, storm-water collections ponds and reservoirs before it is treated to supply drinking water.
- Singapore has an agreement until 2061 to important water from Malaysia.
- NEWater is high-grade recycled water produced from used water that is treated and further purified using advanced membrane technologies and ultraviolet disinfection, making it ultra-clean and safe to drink. Together, Singapore’s four NEWater plants can meet up to 30% of the nation’s current water needs.
