Water cycle Flashcards
What are the two types of system?
Open systems and closed systems.
Give an example of an open system:
A drainage basin- energy from the Sun enters and leaves the system. Water is an input as precipitation, and output as river discharge into the sea.
What cannot enter or leave a closed system?
Matter- it can only cycle between stores.
What can enter or leave a closed system?
Energy- it can be an input or output.
Give an example of a closed system:
The carbon cycle- energy is an input and output, but the amount of carbon on Earth stays the same because there are no inputs or outputs of matter.
What are isolated systems?
Where are these systems not found?
Where neither matter nor energy can enter or leave, and the system has no interactions beyond its boundaries.
These aren’t found in nature.
Natural systems often….
…. have multiple inputs, outputs, stores etc.
What happens when a system is at dynamic equilibrium?
Inputs and outputs are balanced, so flows and processes continue to happen, but in the same way at all times, so there is no overall change to the system.
Why is a system considered to be at dynamic equilibrium and not just equilibrium?
Because, in reality, there are lots of small variations in the inputs and outputs of a system.
These small variations mean that the system is balanced on average and so is said to be in dynamic equilibrium.
Large, long-term changes to the balance of inputs and outputs can cause…
… a system to change and establish a new dynamic equilibrium.
Why might a system change and establish a new dynamic equilibrium?
Due to long-term changes to the balance of inputs and outputs.
In a system, a change can trigger…?
Positive or negative feedback.
What is positive feedback and what does this mean?
Positive feedback mechanisms amplify the change in the inputs or outputs.
This means the system responds by increasing the effects of change, moving the system even further from the previous state.
Give an example of positive feedback:
Temperature rise
Ice covering cold parts of Earth melts due to higher temp
Less ice cover means less of the sun’z energy is reflected
Less of the sun’s energy being reflected means more more is absorbed by the earth
What is negative feedback and what does it mean?
Negative feedback mechanisms counteract the change in the inputs or outputs.
This means that the system responds by decreasing the effects of the change, keeping the system closer to its previous state.
Give an example of negative feedback:
Large amount of CO2 emitted
CO2 in atmosphere increases
Extra CO2 causes plants to increase growth
Plants remove and store more CO2 from atmosphere
Amount of CO2 in atmosphere reduces
What are the major subsystems of the water system?
Atmosphere Lithosphere Hydrosphere Biosphere Cryosphere
What is the cryosphere?
Subsystem of the Earth that includes all the parts where its cold enough for water to freeze, eg. glacial landscapes.
What is the lithosphere?
The outermost part of the Earth.
It includes the crust and the upper parts of the mantle
What is the biosphere?
The part of the Earth’s systems where living things are found.
It includes all the living parts of the Earth, eg plants, animals, birds, fungi, insects, bacteria etc.
What is the hydrosphere?
All the water on earth.
It may be in liquid form, solid form or gas form.
It can also be salty or fresh.
What is the atmosphere?
The atmosphere is the layer of gas between the Earth’s surface and space, held in place by gravity
Where is most fresh water found on Earth?
In the cryosphere, in ice caps, glaciers and permafrost.
Why does the distribution of freshwater storage on Earth create issues for humans?
Most of the freshwater on Earth is stored in the cryosphere.
This is an issue as it means most fresh water is largely inaccessible.
What percentage of fresh water is found in ice caps, glaciers and permafrost?
69%
What percentage of fresh water is found in groundwater?
30%
What percentage of fresh water is found in lakes?
0.25%
What percentage of fresh water is found in soil moisture?
0.05%
What percentage of fresh water is found in the atmosphere?
0.04%
What percentage of fresh water is found in swamps, marshes and wetlands?
0.03%
What percentage of fresh water is found in rivers?
0.006%
What is meant by potable water?
Water that is safe to drink.
What percentage of water is potable?
0.07%
What sort of system can the Earth be considered as?
A closed system- energy is an input from the sun and output to space, but matter is nto an input or output to space.
A cascading system- matter and energy moves between the subsystems (the output of one cycle is the input of the next).
Changes that occur in one subsystem…
… can affect what happens in the others.
How much of the Earth’s water is freshwater?
Less than 3%.
Most of it is saline water.
In order for humans to use it, what must water be?
Physically and economically accessible.
For water to melt or boil….
…. it must gain energy.
Eg. from the Sun.
For water to condense or freeze…
… it has to lose energy.
Eg. to the surroundings.
What is the global hydrological cycle?
Where water is continuously cycled between different stores.
When water is continuously cycled between stores it is known as?
The global hydrological cycle.
What type of cycle is the global hydrological cycle?
A closed system- it has no inputs or outputs.
What are the common characteristics that most systems share?
They have a structure that lies within a boundary.
They are generalisations of reality, removing incidental detail that obscures fundamental relationships.
They function by having inputs and outputs of material (energy and/or matter) that is processed within the components causing it to change in some way.
Interlocking relationships between the atmosphere, lithosphere, hydrosphere and biosphere…
.. have a profound effect on the Earth’s climate and climate change.
What is atmospheric water?
Water found in the atmosphere; mainly water vapour with some liquid water (cloud and raindrops) and ice crystals.
What is cryospheric water?
What is cryospheric water?
The water locked up on the Earth’s surface as ice.
What is oceanic water?
The water contained in the Earth’s oceans and seas but not including such inland seas as the Caspian sea.
What is terrestrial water?
This consists of groundwater, soil moisture, lakes, wetlands and rivers.
Why does oceanic water taste salty?
Why does oceanic water taste salty?
It contains dossolved salts.
The salt in oceanic water allows what to happen?
Allows the waters to stay as liquids below 0°C.
What pH do the salts in oceanic water have?
What has happened to this pH over time?
What is this linked to?
pH of about 8.14 (so they are alkaline).
Over the past 250 years, the pH has fallen and seems destined to continue falling.
This change in pH is linked to the increase in atmospheric carbon and may have a profound influence on marine ecosystems.
What are the locations of cryospheric water?
Give examples.
Sea ice, eg. the Ross Ice Shelf Ice caps, eg. the Iceland ice cap Permafrost, eg. the Alaska North Slope Alpine glaciers, eg. Mer de Glace, France Ice sheets, eg. the Greenland ice sheet.
How does the magnitude of permafrost vary over time?
Over recent years, it has begun to melt and the amount of permafrost on the Earth has reduced.
How does the magnitude of permafrost vary over space?
Found beneath ice-free regions of the Antarctic continent
Also beneath areas in which the ice sheet is frozen to its bed
How has the magnitude of glaciers varied over time?
Sensitive to seasonal climate fluctuations; shrink in summer (providing melt water to local communities) and advance in winter months.
However, since the 2000 the melting of mountain glaciers has accelerated.
How does the magnitude of glaciers vary over space?
Found in deep valleys or upland hollows, mainly around the Arctic Ocean and nearby lands, such as in Greenland
Can be found on any continent, but mainly mountainous and polar regions
Particularly important in the Himalayas
How has the magnitude of ice caps varied over time?
In recent years, the magnitude of ice caps has been rapidly decreasing
For example, Africa’s only remaining ice cap, on Kilimanjaro is rapidly melting and may soon disappear.
How does the magnitude of ice caps vary over space?
Found in mountainous regions of the World; centred over the highest point of an upland area.
Occur all over the world; Himalayas, the Rockies, the Andes and the Southern Alps of New Zealand.
How does the magnitude of ice sheets vary over time?
Over thousands of years, the snow piles up creating thicker and denser ice sheets
Over time, parts of ice sheets are also lost to the sea; as long as it accumulates the same mass of snow it loses to the sea, it will remain stable
However, the general trend over recent years has been that ice sheets are losing more snow to the sea than they are accumulating.
For example, the Greenland Ice Sheet has been increasing negatively since 1995.
How does the magnitude of ice sheets vary over space?
Two major ice sheets are located in Greenland and Antarctica
Greenland Ice Sheet extends about 1.7million km3
Antarctic Ice Sheet extends about 14million km3
How does the magnitude of sea ice vary over time?
Varies seasonally; shrinks in summer and expands in winter
However, over recent years there has been a steady decline in the amount of sea ice; this is because it is closely linked with the planet’s climate
How does the magnitude of sea ice vary over space?
Mainly found in the Arctic Ocean and waters surrounding Antarctica.
Predominantly in the North and South poles
What is it called when a solid turns into a liquid?
Ablation
What is it called when a liquid turns into a solid?
Accumulation
What is it called when a liquid turns into a gas?
What is it called when a liquid turns into a gas?
Evaporation.
What is it called when a gas turns into a liquid?
Condensation
What is it called when a gas turns into a solid?
Deposition.
What is it called when a solid turns into a gas?
What is it called when a solid turns into a gas?
Sublimation.
When state changes occur…
When state changes occur…
… latent heat is either given out or taken in.
The magnitude of each water store…
The magnitude of each water store…
… depends on the amount of water flowing between them.
What does evaporation increase?
The amount of water stored in the atmosphere.
How does the magnitude of the evaporation flow vary over time and space?
If there is a lot of solar radiation, a large supply of water and warm, dry air, then the amount of evaporation will be high.
If there is not much solar radiation, little available water and cool air that is already nearly saturated, evaporation will be low.
What causes condensation to occur?
When air containing water vapour cools to its dew point, condensation occurs.
How does the magnitude of condensation vary over time and space?
Water droplets can stay in the atmosphere or flow to other subsystems; it can form dew on leaves and other surfaces- this decreases the amount of water stored in the atmosphere.
The magnitude of the condensation flow depends on the amount of water vapour in the atmosphere and the temperature.
What are essential parts of the water cycle?
Why?
Cloud formation and precipitation.
Precipitation is the main flow of water from the atmosphere to the ground.
Why do clouds form?
Clouds form when warm air cools down, causing the water vapour in it to condense into water droplets, which gather as clouds.
When droplets get big enough, they fall as precipitation.
What things can cause warm air to cool?
Other air masses: warm air is less dense than cool air. As a result, when warm air meets cool air, the warm air is forced up above the cool air. It cools down as it rises. This results in frontal precipitation.
Topography: when warm air meets mountains, it’s forced to rise, causing it to cool. This results is orographic precipitation.
Convection: when the sun heats up the ground, moisture on the ground evaporates and rises up in a column of warm air. As it gets higher, it cools. This results in convective precipitation
How does cloud formation and precipitation vary over time and space?
Varies seasonally- eg. in the UK there’s normally more rainfall in winter than in summer.
Varies by location- eg.precipitation is generally higher in the tropics than at the poles.
Water droplets caused by condensation are too small to form clouds on their own.
So how do clouds form?
Water droplets caused by condensation are too small to form clouds on their own.
So how do clouds form?
For clouds to form, there must be tiny particles of other substances (eg. dust or soot) to act as cloud condensation nuclei.
They give water a surface to condense on and encourages clouds to form, rather than allowing the moist air to disperse.
Cryospheric processes such as accumulation and ablation change what?
The amount of water stored as ice in the cryosphere.
The balance of accumulation and ablation varies with temperature.
The amount of water stored as ice in the cryosphere depends on what?
Cryospheric processes such as accumulation and ablation.
The balance of accumulation and ablation…
… varies with temperature.
During periods of global cold …
… inputs into the cryosphere are greater than outputs.
Water is transferred to it as snow, and less water is transferred away due to melting.
During periods of warmer global temperatures…
… the magnitude of the cryosphere store reduces as losses due to melting are larger than the inputs of snow.
What type of period is the Earth emerging from?
When did this period reach its peak?
A glacial period.
It reached its maximum 21,000 years ago.
Where are extensive stores of ice on land?
Antarctica and Greenland.
Numerous alpine glaciers are also found here.
Where are large volumes of sea ice found?
In the Arctic and Antarctic.
When do variations in cryospheric processes happen?
Over different timescales.
Can occur over thousands of years, eg. due to Milankovitch cycles.
Can also occur over shorter timescales, eg. annual temperature fluctuations mean that more snow falls in the winter than in the summer.
What factors affect the rate of evaporation?
the amount of solar energy/temperature
the availability of water to evaporate
the humidity of the air
the temperature of the air
How do all plants lose water?
Through transpiration.
What is transpiration?
When water is transported from the roots of the plant to its leaves and out into the atmosphere.
How does amount of solar energy affect the rate of evaporation?
The higher the solar radiation, the more evaporation takes place, as the water has more energy and so can change state.
How does the availability of water affect the rate of evaporation?
The more water that is available, the more potential evaporation can occur.
For example, there is more evaporation from a pond than a grassy field.
How does the humidity of the air affect the rate of transpiration?
How does the humidity of the air affect the rate of transpiration?
The closer the air is to saturation point, the slower the rate of evaporation.
The more water there is in the air already, the less water can evaporate into it.
How does the temperature of the air affect the rate of evaporation?
Warmer vapour can hold more water than cooler air.
So the hotter the air is, the more evaporation can occur.
Explain how frontal rain occurs:
The warm air that moves North from the tropics picks up moisture.
Cold dry air from the poles meets the warm moist air.
Warm and cold air do not mix.
The air masses meet at the polar front where the cold air forces the warm air to rise, creating an area of low pressure.
As the warm air is forced to rise it cools and condenses into cloud at the dew point.
This takes place around 60ºN over the British Isles.
At the top of the troposphere the air moves South and North towards opposite poles.
As the air moves towards the poles, it cools and becomes more dense.
It sinks over the poles creating high pressure and no precipitation.
This cool dry air then travels South towards 60ºN.
What is the ITCZ?
Where warm air from the tropics meet at the equator and creating an area of low pressure.
How does water enter and leave a drainage basin?
It enters as precipitation and leaves via evaporation.
What is the dew point?
What is the dew point?
The temperature at which water vapour condenses, turns into a liquid and creates a cloud.
What can drainage basins be viewed as?
Open, local hydrological cycles.
What is the river’s drainage basin?
What is it also known as?
The area surrounding the river where the rain falling onto the land flows into that river.
Also known as the river’s catchment.
What is the watershed?
The boundary of a drainage basin - any precipitation falling beyond the watershed enters a different drainage basin.
What type of systems are drainage basins?
Open systems with inputs and outputs.
Precipitation
All the ways moisture comes out of the atmosphere.
It is mainly rain, but includes other types like snow, hail, dew and frost.
Interception.
When someprecipitation lands on vegetation or other structures, like buildings and concrete or tarmac surfaces, before it reaches the soil.
What does interception create a significant store of?
Why is it only temporary?
Creates significant store of water in wooded areas.
Is only temporary because the collected water may evaporate quickly, or fall from the leaves as throughfall.
Vegetation storage
The water that’s been taken up by plants.
Surface storage
Water in puddles (depression storage), lakes and ponds.
Soil storage
Soil storage
Moisture in the soil.
Groundwater storage
Water stored in the ground, either in the soil or in rocks.
Water table
Top surface of the zone of saturation.
Zone of saturation
Zone of soil or rock where all the pores in the soil or rock are full of water.
Aquifers
Porous rocks that hold water.
Channel storage
Water held in river or stream channel.
What are infiltration rates influenced by?
Soil type, soil structure and how saturated the soil already is.
Why does overland flow occur?
Because the rain is falling on the ground faster than infiltration can occur.
Baseflow
Groundwater flow that feeds into rivers through river banks and river beds.
Interflow
Water flowing downhill through permeable rock above the water table.
Evaporation
Water turning into water vapour.
Transpiration
The process through which plants and trees take up water through their roots and transport it to their leaves where it evaporates into the atmosphere.
Potential evapotranspiration (PET)
Potential evapotranspiration (PET) The amount of water that cpould be lost by evapotranspiration.
Give an example of where potential evapotranspiration is different to actual evapotranspiration:
In the desert, PET is high (becuase heat increases evaporation) but actural transpiration is low (because there isn’t much water).
How is water balance worked out?
What does general water balance in the UK show?
From inputs and outputs.
UK shows seasonal patterns.
What happens to the water balance in wet seasons, in the UK?
Precipitation exceeds evapotranspiration.
Creates water surplus.
Ground stores fill with water.
More surface runoff and higher discharge, so river levels rise.
What happens to the water balance in the UK during dry seasons?
What does this mean for the end of the dry season and the start of the wet season?
What does this mean for the end of the dry season and the start of the wet season?
Precipitation is lower than evapotranspiration.
Ground stores are depleted, as some is used and some flows into river channel.
So, at the end of the dry season there’s a water deficit. Ground stores are recharged in the next wet season.
What is river discharge?
Volume of water, in cumecs, that flows in a river per second.
What does cumecs mean?
Cubic metres
What increases river discharge?
Why?
High levels of runoff because more water makes it into the river, increasing its volume.
What are hydrographs?
What do they show?
Graphs of river discharge over time.
They show how the volume of water flowing at a certain point in a river changes over a period of time.
What do flood hydrographs show?
River discharge around the time of a storm event.
Peak discharge
The highest point on the graph, when river discharge is at its greatest.
Lag time
The delay between peak rainfall and peak discharge.
Why does lag time occur?
What does a shorter lag time mean?
Happens because it takes time for the rainwater to flow into the river.
Shorter lag time can increase peak discharge because more water reaches the river during a shorter period of time.
Rising limb
Part of the graph running up to peak discharge. It increases as rainwater flows into the river.
Falling limb
Part of graph after peak discharge.
Why does river discharge decrease?
Because less water is flowing into the river.
Describe a flashy hydrograph:
The graph has steep, roughly symmetrical rising and falling limbs.
What factors affect the amount of runoff and the shape of the hydrograph?
Size of drainage basin
Shape of drainage basin
Ground steepness
Rock and soil type
How does the size of the drainage basin affect the amount of runoff anf shape of the hydrograph?
Larger drainage basins catch more precipitation, so have a higher peak discharge than smaller basins.
Smaller basins often have short lag times because precipitation has less distance to travel, so it reaches the main channel more quickly.
How does the shape of the drainage basin affect the amount of runoff anf shape of the hydrograph?
Circular basins are more likely to have a flashy hydrograph than long, narrow basins, as all points on the watershed are roughly the same distance from the point discharge measurement.
So, lots of water will reach the measuring point at the same time.
How does ground steepness affect the amount of runoff anf shape of the hydrograph?
Water flows more quickly downhill in steep-sided drainage basins, shortening lag time.
This also means that water has less time to infiltrate the soil, so runoff is higher.
How does rock and soil type affect the amount of runoff anf shape of the hydrograph?
Impermeable rocks and soils don’t store water or let water infiltrate.
This increases surface runoff.
Peak discharge also increases as more water reaches the river in a shorter period.
What are hydrographs, runoff and the water cycle generally affected by?
Natural causes.
How do intense storms affect:
precipitation and peak discharge?
flows?
runoff?
More precipitation and greater peak discharges than light rain showers.
Larger input of water causes flows to increase in size.
Some flows may not be able to occur rapidly enough for the size of the input, increasing runoff.
Bankfull discharge
The point when the water level reaches the top of the river channel.
How do seasonal changes and vegetation affect the size of inputs, flows and stores?
Winter - temperatures may cause water to freeze, reducing the size of flows through the drainage basins, while the cryosphere grows.
Summer - temperature increases, as does the flows through the drainage basin.
Plants show seasonal variation, affecting amount of interception.
Highest when there’s lots of vegetation and deciduous trees have their leaves.
More vegetation, the more water is lowst before it reaches the river channel, reducing runoff and peak discharge.
What human factors can affect the size of stores in the water cycle?
Farming practices
Land use change
Water abstraction
How can farming practices affect the size of stores in the water cycle?
Ploughing breaks up the surface so more water can infiltrate, reducing the amount of runoff.
Crops increase infiltration and interception compared to bare ground, reducing runoff and increasing evapotranspiration which can increase rainfall.
Livestock trample and compact the soil, decreasing infiltration and increasing runoff.
Irrigation can increase runoff if some of the water can’t infiltrate. Ground water or river levels can fall if water is extracted for irrigation.
How can land use change affect the water cycle?
How can land use change affect the water cycle?
Deforestation reduces water intercepted, increasing amount that reaches surface.
Removal of forest cover leads to decreased infiltration, as nothing is holding the water, allowing it to infitrate the soil rather than run off.
Construction of new buildings and roads creates impermeable layer over land, preventing infiltration.
Massively increases runoff, so flooding is more likely.
How does water abstraction affect the water cycle?
More water abstracted to meet demand, reducing amount stored in lakes, rivers, reservoirs and groundwater.
In dry seasons, even more water is abstracted for consumption and irrigation, so stores are depleted further.
All the ways moisture comes out of the atmosphere.
It is mainly rain, but includes other types like snow, hail, dew and frost.
Precipitation
