Unit 2 And Unit 3: The Water Cycle Flashcards
How does Precipitation Form?
In the atmosphere when water vapour condenses. Condensation requires:
- a small particle, dust or sea salt, in the atmosphere around which condensation can take place. These particles are known as condensation nuclei
- cooling of the air below the dew point. The temperature at which condensation occurs is called the dew point and is dependent upon the humidity of the air.
Why does air cool in the atmosphere?
As altitude increases temperature decreases. Lapse rate - temperature typically drops between 6.5 and 9.8 degrees for every 1000m increase in altitude. Therefore, if air rises or is uplifted in the atmosphere it will cool and subsequently may reach the dew point resulting in condensation and water vapour changing into a liquid or solid.
What is uplift?
Is the process of air rising; as air rises it cools and condenses forming clouds and precipitation.
What are the 3 main mechanisms of air uplift that produce rainfall?
- orographic or relief rainfall
- convection rainfall
- frontal rainfall
What is orographic or relief rainfall?
- Warm, moist air is forced to rise over high areas (mountain ranges)
- Air cools and condenses, forming clouds
- It rains
- Air descends, warms and becomes drier
> occurs in high altitudes
What is convectional rainfall?
- Sun heats the land and the air above
- Warm air rises, cools and condenses, forming clouds
- Rain can then occur
> occurs over land that is subjected to the suns heat - insulation
evaporation
intense
brief thunderstorms
What is frontal rainfall?
> occurs at the boundaries of two air masses of varing temperatures and densities
1. Warmer air gets forced upwards because the old air is denser
2. condensation forms clouds
3. It rains heavily along the front
What are the 2 key mechanisms of precipitation formation with clouds?
The Bergeron-Findeisen theory of ice-crystal growth and the Collison mechanism
What is The Bergeron-Findeisen theory of ice-crystal growth?
- it occurs in clouds where temps are just below 0 degrees; s, operates in high latitude and higher altitudes
1. water droplets can become supercooled and will stay as a liquid below the normal freezing point of 0, yet will only freeze upon contact with a condensation nuclei
2. dust particles act as condensation nuclei allowing droplets to freeze, upon contact with other supercooled droplets these will also freeze, thus enabling hexagonal ice crystals - snowflakes - to start forming.
3. Eventually the large snowflake will become too heavy to be kept aloft by updrafts (rising air) and will begin to fall. As they fall they will pass through warmer air and melt to produce rain
Where does The Bergeron-Findeisen theory of ice-crystal growth commonly occur?
Over the UK where cloud temperatures are often below -5 degrees. If temps close to the ground remain below 2 degrees snow will reach the ground, however if temperatures are above 2 degrees, which they commonly are the snowflakes melt and rain occurs.
Where does the collision mechanism occur?
It explains the formation of rain in the warm tropics where cloud temperatures are too warm for ice crystals to form
What is the collision mechanism?
- supersized condensation nuclei. e.g. large sea salt particles, provide seeds around which very large water droplets form
- the larger super droplets fall and collide with smaller droplets, absorbing them
> this mechanism is often associated with convectional rainfall resulting in heavy downpours and flash flooding from infiltration-excess overland flow
What is excess runoff?
If the rate at which the rain falls is greater than the rate at which it can infiltrate into the ground, then excess runoff will occur. It can be caused by both natural physical factors and human factors
What are natural physical factors which affect excess runoff?
- prolonged rainfall
- intense storms
- snowmelt
- monsoon rains
What are human factors which affect excess runoff?
- deforestation
- urbanisation
Whats an example of a Prolonged Rainfall event?
February 2020 Floods UK
- wettest February on record for the UK
- 5th wettest winter on record since 1862
- three named storms crossed the UK during February, Ciara, Dennis and Jorge.
Why did it rain so much during February 2020?
The type of rain during this period was mainly frontal rainfall. The meeting point between the two air masses of warm tropical air and cold polar air is known as the polar front. Along this front frontal rain will form. The position of this front is controlled by the Jet Stream, stayed over the UK for much of the winter of 2020, hence prolonged periods of rain.
What were some effects of the flooding along River Severn?
- flooding of businesses
- evacuation
- mental + physical illness’ are higher in regularly flooded areas
- in Shrewsbury 70,000 property were at risk of flooding and 1600 property’s were flooded
What is a location example of an intense storm?
Boscastle Flood 16th August 2004
What do intense storms do?
Produce high levels of precipitation and result in flash flooding from infiltration-excess overland flow
What were the key impacts of Boscastle?
- 5 buildings were demolished and 60 more were damaged
- 30 vehicles were washed into harbour
- over 100 people were rescued no-one died
Why did this intense storm at Boscastle happen?
- around 75mm of rain fell in two hours which is the same amount that normally falls in the whole of august
- two types of precipitation occurred which were frontal and orographic
- the torrential rain led to a 2m rise in river levels in one our
- was an intense storm event and was produced as a result of warm moist air from an ex-category 2 hurricane which moved eastwards over the Atlantic ocean
How does geology and topography increase levels of run-off?
- the underlying geology of the catchment is impermeable granite and slate
- Boscastle sits in the bottom of a steep sided valley
How does land use increase levels of run-off?
- deforestation has occurred over much of the catchment which is now used for permanent grazing land which means less vegetation so less interception
- some urban development, impermeable concrete, increased soil erosion
What is the location of the snowmelt case study?
Red River Flooding Of Fargo, 2009 , North of the United States
What are the key points of the Red River Flooding Of Fargo, 2009 case study?
- in march 2009 the Red River flooded in North Dakota and Minnesota in the USA, bringing record flood levels to Fargo at 12.45m on March 28th
- the winter 2008/9 had seen high levels of snow fall and wide spread frozen ground. This was followed by unusually high temperatures which resulted in rapid snow melt
- ice jams - ice carried along by runoff blocks water
- the community helped stop the impacts by volunteers from 100 miles used sandbags to soak up the water
How does snowmelt lead to excess runoff and flooding?
- frozen ground acts as impermeable rock so water cannot percolate/infiltrate
- high temps melt snow
- rapid change in river level
- river bursts its banks
- flashy hydrograph
How does deforestation cause excess runoff?
- grazing animals compact soil, less infiltration and percolation due to less pore spaces
- less vegetation so less water intercepted and less evapotranspiration
- more flashy
What is the deforestation case study?
Haiti, the Caribbean Sea.
It is the poorest country in the western hemisphere
What are the key facts about Haiti?
- in 2008, 4 successive tropical storms and hurricanes hit Haiti , destroying homes, buildings, infrastructure and agricultural crops affecting 800,000 people.
- 793 dead
- 548 injured
- 1923 60% of Haiti was covered by forest, trees protect from impact of storms, prevent soil erosion, and regulate the water cycle.
- less fertile soil for farmers
- now 4% forest cover in Haiti
- hurricane Matthew 2016 cost $2.8 billion in damages
How does urbanisation lead to excess runoff?
Urbanisation renders previously permeable ground surfaces impermeable. Surfaces such as concrete and tarmac (roads + pavements) increase surface runoff/overland flow and decrease rates of infiltration, throughflow and soil storage.
The majority of surface runoff will flow into drains and sewers which will result in a rapid transfer of water into river systems.
What is a water deficit?
A water deficit is experienced when an area lacks sufficient water to meet its needs.
What can water deficits be caused by?
• natural (meteorological)
• human
What is drought?
Drought is an extended period of low or absent rainfall relative to the expected average for a region. Therefore it means different amounts of rainfall in different regions.
What’s a drought in the UK defined as?
A period of at least 15 consecutive days on none of which is there more than 0.2mm of rainfall.
What’s a drought in Libya defined as?
Droughts are recognised only after two years without rain!
What are meteorological droughts caused by?
Variations in the normal atmospheric pressure systems.
What is atmospheric pressure?
Refers to whether air is rising or sinking in the atmosphere.
What’s the pressure when warm air rises?
Low pressure
What’s the pressure when cold air descends?
High pressure
Why is drought linked to extended periods of high pressure over a region?
Where cold air sinks through the atmosphere, it warms, no condensation occurs and consequently no precipitation.
What is the position of the Polar Front controlled by?
The Jet Stream
Explain the position of the Jet Stream
The position of the Jet Stream is not fixed but moves in a series of waves known as Rossby Waves
Why is the position of the Jet stream important?
Because it determines where high and low pressure will occur. As a general rule high pressure will be located to the south of the Jet stream, whereas low pressure will be to the north.
What shape explains the Jet stream?
Omega block
- low pressure in the troughs
- high pressure in the mountain looking blobs
What is the Case Study for Seasonal Variation in Precipitation?
The 1976 UK drought - in the summer of 1976, the UK experienced a record-breaking drought - an extreme water deficit
What are the causes of the 1976 UK drought?
• during the summer & spring of 1976 , the Jet stream was positioned further north than normal, and a blocking high pressure system was located over the UK. This resulted in an extended period of dry weather.
• this summer had been preceded by a dry winter
• high summer temperatures of over 32 degrees occurred for two consecutive weeks. Temperatures peaked at 35.9 degrees in Cheltenham during July and the high temperatures resulted in very high rates of evaporation.
What are some key points about the 1976 UK drought?
• in Dorset they experienced 45 consecutive days without rainfall
• the mid and south if England experienced only 50% of the average rainfall
• Isle of Wight had 20% of average rainfall had fell
• less groundwater - was in recharge
What are some key points about the 1976 UK drought?
• in Dorset they experienced 45 consecutive days without rainfall
• the mid and south if England experienced only 50% of the average rainfall
• Isle of Wight had 20% of average rainfall had fell
• less groundwater - was in recharge
What are some environmental impacts of the 1976 UK drought?
•water being recycled - no rain = no input - no start to water cycle
•reservoirs + lakes drying up
•crops failing - grass disappearing
•fires - quickly spreading
What are some economic impacts of the 1976 UK drought?
•south wales - industries may have to close as they are intensive (iron,paper) but some are hard to be reduced quickly
•south Wales - critical
• 1 gallon of petrol uses 70 gallons of water
What are some social impacts of the 1976 UK drought?
• local authorities checking not watering unnecessary things
• hosepipe bans
• go out physically go collect water so people are restricted to how much they are using so domestic use(restricted to tankers and street stand-pipes) goes down so industry could use it
• farmers had to harvest green beans all in one
• electricity/ heat use decreases
• air conditioning and fans use increases
• heat illness - paramedics
How did the drought affect England, and Wales particularly with figures?
They both received less than 65% of their normal precipitation level.
Wales - 62% of average
Uk - 72% of average
England - 64%
Define ‘megadrought’?
They are multi decade drought events that contained periods of sensitivity and lasted longer than any event observed in the 19th or 20th centuries.
The megadrought is a naturally occurring event that started in the year 2000 and is still ongoing
What is the megadrought case study?
In Western US
By how much have temperatures increased in the western US since 2000?
1.2 degrees
What other weather phenomenoa have made the US drought worse?
•climate change
•EL Niño/La Niña - ocean temps
What other weather phenomenoa have made the US drought worse?
•climate change
•EL Niño/La Niña - ocean temps
What impacts have the US drought had?
• two important reservoirs lake Powell and lake mead (hoover dam) have both sunk dramatically
• increase in wildfires in Southern California
• 70,000 farmers lost jobs
• groundwater (aquifers) have been used to mitigate the impacts - digging deeper - long time to replenish it
What are two reasons why the demand of water has increased?
• growth in global population - 8 billion - need to feed agriculture- majority in Asia since 1820 to 2019
• increased per capita consumption due to increased affluence
What is water scarcity and why does it happen?
Water scarcity is the lack of available fresh water resources to meet demand.
Increased demand can lead to over-extraction of available water which can lead to water deficit or scarcity in some regions.
How many people suffer from high water stress?
Over 2 billion people live in countries experiencing high water stress
What is water stress increases by?
• climate change - rising temps cause glaciers to melt which are supply’s of freshwater
• population growth/ increased affluence/ consumption
• increase water withdrawals
How much water does the average person in an economically developed country typically use in their home per day?
300 litres
- actual consumption 5000L
How is water used in a household day to day?
• washing
• flushing toilets
• laundry
• cleaning
• food preparation/eating/drinking
• dishwashers
What % of the global freshwater is used in agriculture?
70%
What is meant be green water?
Water stored in upper layer of soil after it rains
What is meant be blue water?
Surface water - rivers, lakes
What is the 2nd largest user of water after agriculture?
Industry
What is meant by virtual or indirect water?
Invisible water consumption
1 burger = 2500L
1 cup of coffee = 145L
1 pair of jeans = 8000L
1 T-shirt = 2700L
What is meant by your water footprint?
How much water you use in day to day life
Why does the water that you directly use in your home only represent a small % of your overall water use?
Over 95# is virtual/indirect water that is used in the food and other goods you consume. Some of this water comes from over countries this is known as external water.
What % of the water you consume is virtual external water?
22%
What % of the water you consume is used in agriculture?
92%
What can the human caused water deficits be expressed as?
A ratio of withdrawals to supply
What is an aquifer?
An aquifer is a body of permeable rock which can contain and transmit fresh groundwater.
Where does an unconfined aquifer lay?
Directly below the water table
Where does a confined aquifer lie?
Below a layer of impermeable rock or sediment such as clay and is therefore confined under high pressure.
What will happen if a well is drilled into a confined aquifer?
The water will naturally rise up to the well due to the high pressure it is under, this is known as artesian well.
What happens if the rate of extraction is greater than the rate of recharge?
The water table will drop and untimely the groundwater source will disappear
What is the case study for Aquifer depletion and management?
Californias Central Valley Aquifer
What are some key facts about California?
• it’s one of the USA’s agricultural centres and Central Valley is where 1/3 of the USA’s fresh food is produced
• 80% of California’s water use is in Central Valley and due to recent droughts there has been an increased pressure on Central Valleys aquifer to meet water needs
What are some key facts about California?
• it’s one of the USA’s agricultural centres and Central Valley is where 1/3 of the USA’s fresh food is produced
• 80% of California’s water use is in Central Valley and due to recent droughts there has been an increased pressure on Central Valleys aquifer to meet water needs
What’s some key facts about California’s drought/aquifer depletion?
• record-breaking time without rain
• exceptional drought
• western - more than a decade without rain
• agricultural uses - 75-80% of water is used in agriculture
• teaching people how to be more water wise
• up to 75% of Californias water is from aquifer/groundwater
• 25 million depend on California’s water supply
How has the number of wells in Central Valley changed from 2011 to 2013?
I’m just 2 years 2011-2014 the total number of wells has almost doubled from 1260 to 2460 which puts more pressure on groundwater.
What is the drop in groundwater levels in feet between 1962 and 2015 in California?
The drop level has increased from 0 million of acre-feet lost in 1962 to 53 million acre-feet of groundwater loss in 2015.
When the rainfall seasons were wetter less groundwater was lost -> 15 million acre-feet in 1985
Why have the ground water levels dropped?
•population increases
•higher affluence
•higher amount of intensive agriculture to meet to growing population demand
Describe and explain why much of Central Valley is subsiding
As the below-ground aquifers are drained, the land sinks to partially fill the space left by the removed water. By the late 1970s some areas has sunk about 30feet. Sinking started again in 2008 - dropping at an alarming rate.
2014 - one area had sunk 18 inches in a year.
It’s estimated by 2030 it’ll drop by another 30 feet
How many years would it take for the aquifer to naturally fill?
50 years if everyone stopped pumping groundwater immediately
If everyone stopped pumping water what would the socio-economic issues of this?
• water shortage for 1 year = $2.7billion
• send food prices soaring if farmer stopped pumping groundwater
• people around the world would starve as California is important globally for food
What is artificial recharge?
It involves capturing excess runoff during periods of heavy precipitation and diverting this water into recharge basins or recharge canals.
These basins have porous bases that allow the captured water to percolate down to the aquifer.
What is the case study for artificial recharge?
Californias Pajaro Valley
Give a summary of the Artifical recharge in California?
Stork events lead to excess run-off harder to infiltrate as it’s compact. They collect groundwater, gives it time to percolate.
What’s drip irrigation?
Drip feed plants and crops through metal pipes in soil - 90% efficient
Crop yield is more productive, less water used.
How/when can natural ground water be reacharged?
Aquifers can be replenished naturally over time through precipitation, river bed seepage, flooding and other natural processes including seasonal snow melt. When the rate of percolation is greater than the rate of groundwater flow the water table will rise.
What is the case study for natural groundwater recharge?
London basin - rising groundwater
Describe the geology of the London basin?
Contains a major aquifer: chalk (permeable) located 60m below the surface of central London. Precipitation to the north and south of London results in percolation into the chalk.
How has Londoners aquifer started recharging at a rate of 3m per year?
Due to de-industrialisation, resulting in a reduction in water demand.
What is the problem with the recharging of the London aquifer?
Leads to a problem of flooding in the underground tubes.
• damage to underground tubes, communication cables and sewers.
• soil saturation (clay) - moves infrastructure
• higher population - more houses needed - more development occuring
How is the recharge if the London aquifer managed?
By pumping water (50 ml a day) out if the ground to prevent soil/clay saturation
What is the case study for surface water extraction: Human cause of water deficits?
Aral Sea
What’s the background information of the Aral Sea?
• it’s located between Kazakhstan and Uzbekistan, in Asia
• in 1960 it was the 4th largest body of inland water, fed by two main rivers:the Syr Darga entering from the northeast and the Amu Darya entering from the south.
• by 2014 it was covered just 10% of its original size
Why did Aral Sea begin to disappear?
• Russia developed large scale cotton in Uzbekistan using water for irrigation from the Syr Darya and Amu Darya rivers
• unsustainable overextraction of cotton
• salt in water increased
• water levels dropped by 24m in the Aral Sea
What were some environmental impacts of the disappearance of the Aral Sea?
• animals struggling due to grass being full with salt - camels dying - less food and water for animals
• the salty dust blew off the lakebed and settles into fields, degrading the soil.
• salinity levels from 9.9 to 100%
• droughts
• water level drop from 53.4 to 29
• accelerates climate change - temps over 40
What were some socio-economic impacts of the disappearance of the Aral Sea?
• locals unable to leave - Russians left when sea sank
• jobs were lost - fishing industry disappeared in the 2000s
• population decrease from 510,101 to 1791,1
• camel deaths led to loss of farmers income as they are expensive
• increased poverty led to increased levels of TB due to unclean drinking water
• €150 million of economic losses each year
• locations are 100s of Km away from sea
What were some management solutions of the disappearance of the Aral Sea?
• permanent dam between large and small Aral seas
• Cocarol dam (2005) built by Kazakhstan
• fisheries in North Aral to rebound
• fishermen got financial support
