EQ1 - Water Cycle Processes Flashcards
How is the the global hydrological cycle defined?
The circulation of water around the earth
What is the name of a type of system where there are no external inputs or outputs
(ie the amount of water is finite and constant)
Closed system
Though the amount of global water is finite and constant, what does change about water through the hydrological system?
Its state (liquid, vapour, ice)
The proportions of global water held in each state (water, vapour, ice) varies over time.
True or False?
True - due to climatic changes
What are the 2 types of energy that drive the hydrological system and why?
- Solar Energy
- heat causes evaporation
- Gravitational Potential Energy
- causes rivers to flow downhill and precipitation to fall
How is a store defined?
Reservoirs where water is held
What are the 4 main stores of water in the global hydrological cycle?
- Oceans (largest)
- Glaciers and Ice sheets
- Surface run-off
- The atmosphere
What does ‘surface run-off’ include as a store?
All land-based stores
(rivers, lakes, groundwater etc.)
What is the largest FRESHWATER store?
The cryosphere (glaciers and ice sheets)
What % of global freshwater is held by the cryosphere? (glaciers, ice sheets)
69%
What % of global freshwater is held by the second largest store, surface run-off? (rivers, lakes etc.)
30%
How are flows defined?
The transfers of water from one store to another
How are fluxes defined?
The rates of flow between stores
FLOWS AND FLUXES DATA
What does the global water budget account for?
All of the water held in STORES and FLOWS
What % of the global water budget (all water) is freshwater?
2.5%
How much of all freshwater within the global water budget is considered ‘easily accessible surface freshwater’?
Only 1% of all freshwater
Where is 70% of all global freshwater ‘locked up’?
Glaciers and Ice sheets (cryosphere)
What is ‘residence time’ in the hydrological cycle?
The average time a molecule of water will spend in one of the stores
What are the average ‘residence times’ in the (1) atmosphere, (2) oceans, and (3) ice caps?
10 days in the atmosphere
up to 3,600 years in the oceans
15,000 years in an ice cap
What are the 2 water stores that are believed to be non-renewable? (depletable)
Fossil Water and the Cryosphere
What is ‘Fossil Water’
Deep groundwater from pluvial (wetter) periods in the geological past
How is ‘the cryosphere’ defined?
Areas of the world where ice/snow is present for part of the year
Why may the cryosphere not be ‘non-renewable’?
If another glacial period occurs, more water will become locked in the cryosphere
What is the most alarming figure for humans about the global water budget?
Only 1% of freshwater is accessible
What are the 3 types of rainfall?
- Convectional
- Frontal
- Relief (orographic)
Explain the process of Convectional rainfall
- Sun warms the ground
- Evaporation
- Warm air rises
- Rising air cools
- Cool air condenses (clouds)
- Falls as rain
Explain the process of Frontal rainfall
- Warm air mass meets cold, denser air mass (known as a front)
- Warm air rises over cold air
- Rising warm air cools
- Moisture condenses as cloud
- Rainfall
Explain the process of Relief rainfall
- Warm air travels inland
- Air meets mountains and is forced upward
- Upward air cools at altitude
- Rain falls on the windward side of mountain
Where in the world is convectional rainfall common?
Tropical rainforests
Where in the world is frontal rainfall common?
The UK
Where in the UK is relief rainfall common?
The North/North West - coastal areas with high relief
(e.g Lake District, Scottish Highlands)
What is the main ‘input’ into the hydrological cycle?
Precipitation
How does type of precipitation (e.g snow) affect the speed of drainage with the hydrological cycle?
Varies in speed due to precipitation state
e.g Snow takes time to melt back into water
How does precipitation intensity affect the drainage basin?
More likely to flood
How does seasonality influence the drainage basin?
Drainage basin system operates at different ‘flow’ levels at different times of the year
Define interception (flow)
The retention of water by plants
- this water is eventually evaporated or absorbed by vegetation
Define infiltration (flow)
Where water is absorbed by the soil
Define Percolation (flow)
The deeper transfer of water into permeable rocks
- (similar to infiltration but deeper)
Define throughflow (flow)
The movement of water downhill, through the soil
Define groundwater flow (flow)
Very slow movement of water through deep permeable rocks
- occurs after percolation has happened
Define surface runoff (flow)
Movement of water over the surface
- this flow is unconfined by a channel, differing it from a river
Define river/channel flow (flow)
Movement of water within a confined channel
Define ‘Input’ to the Hydrological system
Addition of water to a specific part of the system
Define ‘output’ to the Hydrological system
Redistribution of water from one part of the system to another (e.g evaporation)
- remember, water is CONSTANT - output is not a reduction in total water
Define evaporation (output)
Process where moisture is lost directly into the atmosphere
- this can be from water surfaces, soil or rocks
Define transpiration (output)
Process by which water is lost to the atmosphere through plants
Define discharge (output)
Channel flow into another larger area
- this could be a larger drainage basin, lake or sea
What is a drainage basin?
Area of land drained by a river and its tributaries
- also known as a river catchment
What is the name given to the boundary of a drainage basin?
Watershed
The drainage basin is a subsystem within the hydrological system.
True or False?
True
What type of system is the drainage basin?
It has external inputs and outputs
Open system
The amount of water in a drainage basin doesn’t vary with input (precipitation)
True or False?
False - more input (precipitation) causes more water stored in the basin
How does climate affect the hydrological system?
Influences the amount of inputs (precipitation) and outputs in the system
How does climate affect vegetation?
Decides the type/cover of vegetation
- Tropical amazon has more interception than UK
How do soils affect the hydrological system?
Affect flows within the system
e.g infiltration, throughflow and surface run-off
What do more permeable/less permeable soils allow for? (types of flow)
More permeable soils = more infiltration and throughflow
Less permeable soils = more surface run-off
How does geology affect the the hydrological system?
Affect subsurface flows within the system
- due to variations in permeability of rocks
How do permeable/impermeable rocks affect groundwater stores?
Permeable rocks allow for percolation - water can reach groundwater stores
Impermeable rocks limit percolation - restricting groundwater supply
What 2 ways does relief influence the hydrological system?
- Encourages orographic (relief) rainfall
- Increases surface run-off
How does relief affect the amount of infiltration?
Steeper slopes accelerate run-off and allow no opportunity for infiltration
What 4 ways does vegetation impact the hydrological system?
- More interception
- Reduced surface run-off
- More transpiration
- More infiltration (slows movement of water to soil)
How does the presence of vegetation impact flows?
- Reduces surface run off
- More interception and infiltration
What are the 5 physical factors that influence the drainage basin?
- Climate
- Soils
- Geology
- Relief
- Vegetation
What 2 things do humans most often modify which disrupts the drainage basin system?
- Rivers
- Ground surface (shape, texture, coverage etc.)
Man-made changes to the drainage basin system, (often by modifying Rivers or the Ground surface) accelerate processes acting within it.
True or False?
True
How does construction of storage reservoirs affect the drainage basin?
Holds back channel flows
- as more water is held back, less flows downstream
How does the abstraction of groundwater for irrigation affect the drainage basin?
Reduces groundwater stores
What 2 ways does deforestation affect the drainage basin?
- Reduces evapotranspiration
- increases surface run-off
How does changing land use from arable (crops) to pastoral (livestock) affect the drainage basin?
Livestock compact soil
- more surface run-off
- less infiltration
How does changing land use from pastoral (livestock) to arable (crops) affect the drainage basin?
Ploughing loosens soil
- more infiltration
- less surface run-off
How do urban surfaces impact the drainage basin?
Urban surfaces are impermeable (e.g tarmac, tiling)
- More surface run-off
- Less percolation and infiltration
How do man-made drains affect the drainage basin?
Rapidly deliver rainfall to channels
- reduced time lag
- higher chances of flooding
What 4 human practices accelerate processes within the drainage basin?
- River Management
- Deforestation
- Agricultural land use
- Urbanisation (surfaces, drains etc.)
Which tropical drainage basin has been severely impacted by deforestation?
The Amazon Basin
How has deforestation caused lower humidity in the Amazon?
Reduced number of trees has decreased transpiration
How has deforestation caused reduced precipitation in the Amazon?
Lower humidity has affected cloud formations, and in turn precipitation patterns
How has deforestation caused increased surface run-off in the Amazon?
Fewer trees to intercept precipitation means there is more surface run off
How has deforestation caused reduced infiltration in the Amazon?
Loss of tree roots and organic matter makes the soil less permeable
How has deforestation caused more evaporation in the Amazon?
Soils and water bodies become more exposed without tree cover and evaporate quicker
How has deforestation caused more soil erosion?
Vegetation and roots stabilise soils - without vegetation soils are vulnerable to erosion
How has water quality and aquatic life been harmed by more soil erosion, caused by deforestation in the Amazon?
Eroded soil (due to less vegetation) means more silt is washed into river channels
What is the water budget?
The annual balance between inputs and outputs in the hydrological cycle
What is the formula used to calculate the water budget?
(remember it is the balance between inputs and outputs)
P = E + R +/- S
Precipitation
Evapotranspiration
Run-off
Storage (change)
Define evapotranspiration
The combined loss of water from the Earth’s surface (ie total output)
- made up of evaporation (water and soil) and transpiration (plants)
Why are regional/national water budgets important to calculate?
Provide an indication of the amount of water available for human use
- this can then be shared between agriculture, industry or domestic use)
Why are local water budgets beneficial?
They inform about available soil water
What is the name given to the amount of water that can be stored in the soil and is available for growing crops?
Available soil water
Why is available soil water useful for Farmers?
Used to identify when/how much irrigation is required for crops
THEN THERE IS ALSO A WEIRD DIAGRAM THING (5.3A)
What is a river regime?
The annual variation in discharge/flow of a river at a certain point
What is a river regime (variation in discharge/flow) measured in?
Cumecs
What 6 factors affect a river regime?
- Size of river
- Amount, seasonality and intensity of precipitation
- Temperature
- Geology and soils (permeability)
- Type of vegetation cover
- Human activities
How does the location (lower/upper course) of a river discharge measurement influence it’s regime?
Affects volume and variability of flow
e.g lower course has higher volume than upper course
How does precipitation affect a river’s regime?
Determine flow patterns and therefore discharge
- more intense rainfall causes higher discharge
How do temperatures influence a river’s regime?
Impacts amount of meltwater from snow
Impacts rate of evaporation (especially during summer)
How do more permeable/porous geology and soils affect a river’s regime?
Allows for more groundwater flow, maintaining base flow
How does vegetation type (e.g wetlands) influence river regime?
Wetlands hold water and release it slowly into the river, reducing discharge
How do human activities (e.g dams and river management) influence a river’s regime?
These activities aim at regulating discharge, altering river flow
River regimes show discharge changes over the period of a year.
What do storm hydrographs show?
Discharge changes over a short period of time (e.g a storm)
- often just a few days
What 2 things are plotted on a storm hydrograph?
- Precipitation - x axis (short burst of rainfall)
- Discharge - y axis
What does the ‘rising limb’ show on a hydrograph?
The sharp increase in river discharge following heavy precipitation
What is ‘peak discharge’ on a hydrograph?
The highest point on the hydrograph
- shows maximum river flow post-rainfall
Define ‘lag time’ on a hydrograph
The delay between peak rainfall and peak discharge
What does the ‘falling limb’ show on a hydrograph?
The decrease in river discharge as rainfall stops and water drains
What is base flow on a hydrograph?
The normal, steady flow of a river
- supplied mainly by groundwater
The shape of a storm hydrograph of the same river remains the same year round.
True or False?
False - varies each time rainfall (storm) occurs
What are hydrographs with very steep limbs, high peak discharge, and short lag times referred to as?
‘Flashy’ Hydrographs - the whole process occurs rapidly
What are hydrographs with gently inclined limbs, low peak discharge, and a long lag time referred to as?
‘Flat’ Hydrographs - the process is much more drawn out
What one factor contributes most to creating ‘flashy’ hydrographs?
Urbanisation
How does construction work make hydrographs more ‘flashy’ ?
Leads to removal of vegetation cover and more exposed soil
Exposed soil reduces infiltration and increases surface run-off
How does concreting and tarmac make hydrographs more ‘flashy’?
They are impermeable and don’t allow for infiltration
- therefore there is more surface run-off
How does building density make hydrographs more ‘flashy’?
Roofs intercept rainfall and channel into drains
How do drains and sewers make hydrographs more ‘flashy’?
They rapidly funnel rainwater into river channels
How does river channelisation make hydrographs more ‘flashy’?
Straightened river channel means peak discharge is reached quicker
- lag time is very short
How can bridges sometimes affect storm hydrographs?
They can restrain floodwater and act like dams
- causes a delay downstream
- also delays peak discharge, as water takes time to pass through the bridge
What is the overall danger of urbanisation and it’s influence on ‘flashy’ hydrographs?
Increased flood risk
What geographical factor makes urban areas even more prone to flooding?
Cities and towns often built in close proximity to them
- historically due to trade, water supply and sewage disposal
Why are planners becoming important players in managing the impacts of urbanisation on flood risk?
- Many towns and cities are natural prone due to location
- Population densities mean there are high numbers of vulnerable people
- high property values and assets in urban areas
What 3 methods are planners and authorities using to manage flood risk?
- Modifying/strengthening embankments
- Flood emergency procedures
- Land-use zoning
What rock type leads to a ‘flashy’ hydrograph?
Impermeable rock (e.g granite)
- restricts percolation
What rock type leads to a ‘flat’ river?
Permeable rocks (e.g limestone)
- allow for percolation
What type of soils lead to a ‘flashy’ hydrograph?
Clay soils (low infiltration)
What type of soils lead to a ‘flat’ hydrograph?
Sandy soils (high infiltration)
What type of relief leads to a ‘flashy’ hydrograph?
Steep slopes
- promote surface run-off
What type of relief leads to a ‘flat’ hydrograph?
Gentle slopes
- allow for infiltration and percolation
What Basin size leads to a ‘flashy’ hydrograph?
Small basins
What basin size leads to a ‘flat’ hydrograph?
Larger basins
What shape basins lead to ‘flashy’ hydrographs?
Circular basins
- funnel water more rapidly to a river channel
What shape basins lead to ‘flat’ hydrographs?
Elongated basins
- takes longer to reach river channel
Hydrographs measure discharge at any 1 given point on the river course.
True or False
True
- they don’t show discharge variation at different parts of a river
How does an already wet (saturated) basin lead to a ‘flashy’ hydrograph?
Saturation allows for less infiltration/percolation
How does a previously dry (unsaturated) basin lead to a ‘flat’ hydrograph?
Unsaturation means infiltration/percolation can occur
How does low density vegetation lead to a ‘flashy’ hydrograph?
Lower levels of interception
- more surface run off
How does high density vegetation lead to a ‘flat’ hydrograph?
Higher interception levels
- slower movement through the system
- more water lost to transpiration
