Water Flashcards
What are the 5 stores in the global hydrological cycle?
Ocean
Atmosphere
Cryosphere
Groundwater flow
Lake/reservoir
What are the 9 flows in the global hydrological cycle?
Evaporation
Condensation
Precipitation
Evapotranspiration
Interception
Surface run-off
Through flow
Infiltration
Percolation
What is the difference between infiltration and percolation?
Infiltration is when water travels through the top layers of soil. Percolation is when water travels through deeper soil layers.
What are the 2 types of water stores?
Blue water (liquid form)
Green water (in vegetation + soil)
What are flows?
Physical mechanisms changing the flux (rate of flow) between stores
Why is the global hydrological cycle a closed system?
Fixed volume of water in the earth-atmosphere system
No external input/output
But water can exists in different states
What 2 processes drive the global hydrological cycle?
Solar energy
Gravitational potential energy
In 3 steps, how does solar energy drive the global hydrological cycle?
- Water on the surface/in plants is heated and evaporated
- Humid air rises but condenses at a cooler temperature to form clouds
- Precipitation returns water to land/oceans
How does GPE drive the global hydrological cycle?
Converted to kinetic energy and water falls as precipitation, or rivers flow downstream to ocean
What % contribution does the ocean water store have? Evaluate
96.9%
Drives huge precipitation, but water is saline
What % contribution does the cryosphere water store have?
1.9%
large store, but not accessible to use
What % contribution does the groundwater and surface water water store have?
1.11%
Keeps vegetation alive, holds 30% of freshwater stores
What % contribution does the atmosphere store have?
0.001%
Small but provides opportunity for precipitation (freshwater)
What % contribution does the biosphere water store have?
0.0001%
Small but regulates environment and climate
When temperature is higher (summer), how do the ocean, atmosphere, and land stores flux?
Atmosphere store increases
Ocean/land stores decrease
When temperature is lower (winter), how do the ocean, atmosphere, and land stores flux?
Ocean/land stores increase
Atmosphere store decreases
What is the global water budget?
Takes into account all water held in stores/flows of the hydrological cycle
However, only 2.5% is freshwater
Of that, only 1% easily assessible
What is residence time?
Average time a water molecule spends in a store
Which stores have a short residence time?
Biosphere- 1 week
Atmosphere- 10 days
Surface water- 2 weeks-10 years
Which stores have a long residence time?
Ocean- 3600 years
Groundwater- up to 10,000 years
Cryosphere- 15,000 years
Why are water stores with a longer residence time more easily polluted?
In situ for longer, more exposure
What is fossil water?
Ancient, deep groundwater from pluvial (wet) periods in geological past
Undisturbed for over a millenia
What are the 8 parts to a drainage basin?
Source
Tributary
Confluence
River/channel
Watershed
Drainage basic
Mouth
Sea/lake
What are the 3 types of input to the hydrological cycle? (precipitation)
Cyclonic/frontal
Orographic
Convectional
What is cyclonic/frontal rainfall?
Warm air is lighter and less dense so is forced to rise over cool air (low pressure)
Cools and condenses to form clouds
Rains along front
What is orographic rainfall?
Warm air is forced to rise over a mountain
Cools and condenses at high altitude
Rain falls on slope facing wind direction
Leeward slope has little rain (rain shadow)
What is convectional rainfall?
Sun heats the land, and air above it becomes warmer
Warm air rises and its ability to hold water vapour decreases
Cools and condenses, then heavy rainfall
What are 2 factors that could affect the input (precipitation patterns)?
Space (mountains vs tropics; continentality = drier)
Time (season; intensity; climate change on long-term scale)
What does the flow interception depend on?
Trees in full-leaf season
What does the flow infiltration depend on?
Rain volume, saturation level, angle
What does overland flow depend on?
Precipitation intensity > infiltration rate
What is saturated overland flow?
When soil/urban drains full (or backed) so cannot infiltrate
What does throughflow depend on?
Porus, sandy soils
What does the flow percolation depend on?
Permeable/porous rock
Greater in humid climates with vegetated slopes
What does groundwater flow depend on?
Permeable/porous rock increases rate of flow
What are the outputs of the hydrological cycle?
Evaporation + transpiration (evapotranspiration)
Channel flow
What are the 5 physical factors within drainage basins that determine the relative importance of inputs flows and outputs?
Climate
Soils
Geology
Relief
Vegetation
How does climate determine the relative importance of inputs flows and outputs?
Influences type/amount of precipitation
Influences evaporation
Also impacts vegetation type
How do soils determine the relative importance of inputs flows and outputs?
Determines the amount of infiltration and throughflow
Indirectly determines vegetation type
How does geology determine the relative importance of inputs flows and outputs?
Impacts on sub-surface processes (percolation and GW flow)
Indirectly alters soil formation
How does relief determine the relative importance of inputs flows and outputs?
Altitude impacts on precipitation totals
Slopes can affect amount of runoff
How does vegetation determine the relative importance of inputs flows and outputs?
Presence/absence affects interception, infiltration and overland flow
Also affects transpiration rate
In what 4 ways can humans disrupt the drainage basin cycle?
Urbanisation
Deforestation
Creating water storage reservoirs
Overabstraction
How does urbanisation disrupt the drainage basin cycle?
Impermeable layer so direct overland flow
Thus, less infiltration and percolation
Less evapotranspiration -> reduced rainfall
How does deforestation disrupt the drainage basin cycle?
Reduced interception = reduced EVT = reduced rainfall
Also no roots to bind soil, so it erodes/compacts
Direct runoff/overland flow increase speed of cycle (possible floods)
Give background to deforestation in the Amazon
Over 20% destroyed, rate accelerating
What are 2 impacts of deforestation in the Amazon?
Normally 75% intercepted water, decreases to 25% when the dense canopy is cleared
Soil is now thin and vulnerable to erosion and tropical rains, so farmers relocate
What are some issues of reservoirs?
Decreases the river flow downstream, forests die
Salinity levels and pollution level increases
What are some issues with the reservoir created from the Three Gorges Dam?
Low water quality
1.3 million people relocated
What is the issue with overabstraction in Israel?
Water struggles to infiltrate down to the groundwater store, reducing store
20% reduction in ground for rainwater to infiltrate
Marine aquifers are salty and merge with drinking water aquifers
When the drainage basin urbanised, aquifers aren’t recharged
What are the 4 parts of the water budget graph?
Soil moisture recharge
Soil moisture surplus
Soil moisture utilisation
Soil moisture deficit
Regarding the water budget graph, what is the best condition for growing?
Soil moisture utilisation
What is the water budget graph?
Balance of inputs and outputs in a drainage basin
What is the equation for water budget?
Change in storage = precipitation - (runoff + EVT)
What does a river regime show, and how is it measured?
Difference in discharge of river throughout the year
A flow of volume, measured in cumecs (cubic metres/sec)
What can affect river regimes?
Climate/latitude- affects meltwater/evaporation rate
Geology + soils- permeability/porosity, GW regulates flow
What are long complex river regimes?
When drainage basin crosses several relief and climatic zones
Give information about the variation in discharge in the Amazon River, South America
Moderate seasonal variability, but always high discharge
Rainforest climate (wet/drier seasons)
EVT levels high, but so is conventional rainfall
Dams have little effect
Give information about the variation in discharge in the Yukon River, USA
High seasonal variability
High summer temp and high mid-lat rainfall + snowmelt
Snow refreezes around September
Some HEP but little human influence
Give information about the variation in discharge in the Murray-Darling River Australia
High seasonal variability
Sub-tropical/monsoon climate
Suffers from mid-lat depressions in wet season, not in dry
High relief, a lot in drought from rain shadow
Lots of irrigation drawing water
What is lagtime on a storm hydrograph?
Time between peak rainfall and peak discharge
What 6 physical features of a drainage basin does the shape of a storm hydrograph depend on?
Size
Shape
Drainage density
Soil/rock type
Relief
Vegetation
How does size of drainage basin affect the shape of a storm hydrograph?
Small
- discharge peaks quick, but low
- as fills quickly, but small volume
Large
- slow, but high
- water has longer distance to travel to river, but more water
How does shape of drainage basin affect the shape of a storm hydrograph?
Elongated
- discharge peaks slow + low
- takes longer to travel down
Circular
- quick + high
- less distance for rain to travel from where it fell
How does drainage density (number of tributaries) of drainage basin affect the shape of a storm hydrograph?
High
- discharge peaks quick + high
- point of rainfall close to river so fills quick
Low
- slow + low
- longer to travel so may infiltrate/intercept
How does soil/rock type of drainage basin affect the shape of a storm hydrograph?
Impermeable
- discharge peaks quick + high
- can’t infiltrate so flows quick as overland flow
Permeable
- slow + low
- some ‘lost’ to infiltration
How does relief of drainage basin affect the shape of a storm hydrograph?
Steep
- discharge peaks quick + high
- gravity speeds flow
Gentle
- slow + low
- water travels slowly to river, more likely to infiltrate
How does vegetation in drainage basin affect the shape of a storm hydrograph?
Bare
- discharge peaks quick + high
- rain hits ground directly to flow to river, oversaturation may also occur
Forest
- slow + low
- can store water or slow flow
How does urbanisation of a drainage basin affect the shape of a storm hydrograph?
Discharge peaks quick + high as impermeable land, quick overland flow
How does agriculture in a drainage basin affect the shape of a storm hydrograph?
Discharge peaks quick + high as furrows channel water
How does deforestation in a drainage basin affect the shape of a storm hydrograph?
Discharge peaks quick + high as trees can’t trap water and slow flow
What is the role of planners in managing land use in drainage basins?
- determines if development increases flood risk
- have to show that land-use change doesn’t increase runoff beyond estimation for a greenfield site
- give weight to environmental considerations and need for development
Sustainable drainage systems (SuDS) can decrease runoff eg:
1. Greenroofs
2. Permeable pavements
3. Rain water harvested + recyled
What is meteorological drought?
Degree of dryness compared to normal precipitation
Rainfall deficit
What is hydrological drought?
Drainage basins suffer shortfalls, rainfall deficit affects water supply
Evident in reduced GW levels, river flow etc
What is agricultural drought?
Insufficient water for crops, they wilt without irrigation
How do blocking anticyclones cause meteorological drought in the mid-latitudes?
Large subsiding air masses break away from the ferrel cell into mid-lats bringing high pressure
Usually rainy as polar maritime + tropical maritime airmasses meet, polar/tropical continental airmasses are rarer and cause the high pressure when they break away from normal cells
What conditions do blocking anticyclones/high-pressure zones bring to the UK in summer/winter?
Summer- hot + dry
Winter- bitter cold + frost from absence of clouds
Give some facts from the 2003 Paris drought
3 week blocking anticyclones
15,000 killed from dehydration + heatstroke, mostly elderly
What are some longer-term trends for blocking anticyclones?
Drought persistent in European summer over the last 2 decades
Climate change increases temp –> larger BAC
How is hydrological/agricultural drought caused in semi-arid zones?
In intertropical convergence zone (ITCZ) sun rays concentrated, rainfall high- 300km wide
ITCZ moves north/south, providing 12 week wet season. H+A drought conditions for 9 months
How can meteorological drought be caused in semi-arid zones?
If a blocking anticyclone of high pressure in the ITCZ blocks the arrival of the wet season
What are some longer-term trends for drought in semi-arid zones?
Land conversion collapses local water cycle, thus just seasonal wet season
Climate change increases temp –> larger BAC, unreliable wet season
What are 2 other causes of dry land (not latitude)?
Rain-shadow effect
Continentality (far removed from rain-bearing winds)
What are ENSO cycles?
El niño southern oscillations (changes in conditions in Pacific Ocean)
What are teleconnections?
Knock-on effects of El Niño worldwide
What happens in an El Niño event?
- Trade winds weaken and lead to eastward flow
- Warm water stays near South America, cold Humboldt current suppressed
- Warm water rises, cools and condenses to form clouds + heavy rain over South America (low pressure), flood risk
- Air circulation reverses
- Warm water near Australia moves eastward, reinforcing El Niño
- Australia has cool water and high pressure, risk of droughts and fires
How often do El Niño events occur?
Every 3-7 years
Frequency increasing due to climate change
How long do El Niño events typically last?
9-12 months
When was the latest El Niño event?
Started in summer 2023
What happens in a La Niña event?
Stronger trade winds, so neutral conditions intensify
Severe drought in South America
When was the last La Niña event? When can they occur?
2010/11
Can follow El Niño- this followed 2009/10 El Niño
How has desertification occurred in the Sahel?
- Colonialism + population growth –> shift from mainly nomadic to rain-red agriculture
- Land conversion- deforestation + agriculture
- More cattle- overgrazing + land conversion
- Soil exposed, increased soil erosion
- Agriculture leads to overcultivation
- Even less crops can grow, reduced EVT –> less local rainfall
Wet season also unreliable due to climate change
Leads to desertification, all encouraging over-abstraction
What are 3 socioeconomic causes worsening the desertification cycle of decline in the Sahel?
Poverty- no other choice of jobs
Civil wars/conflict- destroys land
China into Africa- takes best land, pushes farmers to worst-effected parts
What are some consequences of the 2015/16 El Niño Ethiopia (teleconnections)? (Sahel)
PS: a lot from aid fatigue too
Malnutrition
Vulnerable to disease from dirty drinking water eg: Cholera
100,000 displaced
What are 4 physical factors causing drought in Australia?
High-pressure
El niño
Continentality
Rain-shadow
What are the 2 ways humans contribute to drought in Australia?
Over-abstraction of surface + ground water: drought from high-tech water management in the Murray Darling basin
Over-abstraction of groundwater –> salinisation: large commercial farms in the southeast
Give background information on the Murray Darling Basin
Size of France and Spain
Provides 75% of Australian water
5x increase in extractions in last 100 years
How is the Murray Darling Basin managed?
30 dams to create reservoirs for irrigation, helps water variability
1974 Snowy Mountain Project is a water transfer project (series of dams, pipelines, reservoirs). Moves water from less used drainage basin (Snowy river) to in-demand drainage basin (Murray Darling River). Expensive and complex as water is pumped against gravity
What are 4 stakeholders who benefit from management in the Murray Darling Basin?
Commercial farming (before the Big Dry)
Residents of the MDR drainage basin
Government as increases drinking water supply
Fishing
What are 3 reasons why the management of the Murray Darling basin is not sustainable?
- Reduced river flow results in salinisation
- Ecosystems lost
- Eutrophication
How do commercial farms in Australia lead to salinisation via over-abstraction?
- Land cleared and replaced with crops
- Irrigation systems often used, rain fills up groundwater and raises water table. Heat pulls water table up more. This is capillary action
- Water table reaches the surface and the groundwater is salty due to being in natural rock
How can salinisation in Australia be fixed?
Sometimes high-tech solutions used to wash out the salt