Water cycle Flashcards
What % of earth’s water is in oceans?
97%
What is the PH of ocean water?
8.14 fallen from 8.25 over last 250 years
What are the 5 locations of cryospheric water
- sea ice
- ice caps
- ice sheets
- permafrost
- alpine glaciers
Why does sea ice not increase sea levels?
Its formed from sea water
What is an ice sheet?
Mass of glacial land ice extending over 50,000km2
Where are the 2 major ice sheets?
Greenland and Antarctica, 99% of freshwater ice
How are ice sheets formed?
Snow falls and does not completely melt, over thousands of years layers of snow pile up into thick masses of ice
What are ice caps?
Thick layers of ice under 50,000km, usually found in mountainous areas
What are alpine glaciers?
Thick masses of ice found in deep valleys or in upland hollows
What is permafrost?
Ground that remains below 0 degrees for at least 2 consecutive years (occurs in glacial periods)
What are the 4 classes of terrestrial water?
- surface water
- groundwater
- soil water
- biological water
What is surface water?
Free-flowing water of rivers as well as water from ponds and lakes
What are rivers?
- act as store and transfer of water
- streams of water within a defined channel
- cover 0.0002% of all water
What are lakes?
Collections of fresh water found in hollows on the land surface. Larger than 2 hectares.
What are wetlands?
- areas of marsh, fen and peatland
- dominance by vegetation
What is groundwater?
Water collects underground in the pores spaces in rock, depth of 4,000m
What is soil water
- Held together with air in unsaturated upper weathered layers of the Earth
- Fundamental for many hydrological and biological processes
What does soil water effect?
- weather/climate
- run-off potential
- flood control
- soil erosion
- reservoir management
Why is soil moisture important?
Controls exchange of water and heat energy between the land surface
Important role in weather patterns
What is biological water?
Constitutes the water stored in all the biomass
How many states can atmospheric water exist in?
3
solid, liquid and gas
What is evaporation?
Liquid->gas
Solar energy hits surface of water causing evaportation
What factors affect the rate of evaporation?
- solar energy
- availability of water
- humidity of air
- temperature of air
What is transpiration?
Water is transported from roots of plants to leaves and then lost through pores (stomata) on leaf surface
What is condensation
Gas->liquid
-occurs at dew point
What are the 2 main cryospheric processes?
accumulation and ablation
What period are we in now?
Quaternary period
What has happened during the quaternary period?
- Glacial periods where the sea level was 120m lower than now
- Interglacial periods where ablation exceeds accumulation
What is ablation?
Loss of mass of ice, melting
What is accumulation?
Build-up of ice mass,freezing
What is a drainage basin?
Area of land drained by river and its tributaries
What is groundwater flow
Slow movement of water through underlying rocks
What is infiltration?
Downward movement of water from the surface to soil
What is interception?
Precipitation that falls on vegetation surfaces cover that is temporarily stored on these surfaces
What is overland flow?
When water flows over the surface when the soil is full
What is percolation?
Downward movement of water within the rock under the soil surface, rates depend on nature of the rock
What does saturated mean?
Any water store that has reached its maximum capacity
What is stemflow?
Movement of water up or down a tree or plant
What is throughflow?
Movement of water through soil layer
What is throughfall?
Water from leaves to ground falls by throughfall
What factors affect infiltration?
- gravity
- relief
- capillary action
- soil porosity (texture, structure)
- topography
- vegetation
What is soil storage?
Amount of water that can be stored in the soil
How does soil store water?
It consists of solid particles with pore spaces between them which can be filled with water
Define saturated
When the infiltration capacity has been reached
What is an input to the drainage basin?
Precipitation
What is an output of the drainage basin?
- run-off
- evapotranspiration
- soil/groundwater storage
What are the 2 main parts of the water budget?
Precipitation and potential evapotranspiration
What is potential evapotranspiration?
Amount of water than could be evapotranspiration from an area if there was enough water
What is bankfull?
Maximum discharge that a river channel can hold without flooding
What does salt in water do?
Allows oceanic water to stay as a liquid below 0 degrees
What is SUDR?
- surplus
- utilisation
- déficit
- recharge
What is soil moisture surplus?
Precipitation is greater than potential evapotranspiration, all space in soil has been filled and can cause flooding
What is soil moisture utilisation?
Potential evaporation exceeds precipitation, water store is being used by plants
What is soil moisture deficit?
Deficit of soil water, plants wilt or have adaptations to survive dry conditions
Potential evapotranspiration is higher than precipitation but getting lower
What is soil moisture recharge?
Precipitation is greater than potential evapotranspiration, soil water will start to recharge
What is baseflow?
Represents the average day-to-day discharge
What is storm flow?
Discharge resulting from storm precipitation
Why is knowledge of discharge important?
- design of water related structures
- developing hydroelectric power
- flooding
- drought episodes
What is a gauging station?
Places where scientist test terrestrial bodies of water
What is river regimes?
Variability in river discharge throughout the course of the year
What causes the the river regime the change?
- precipitation
- temperature
- evapotranspiration
- drainage basin characteristics
What physical factors affect storm hydrographs?
- relief
- high drainage density
- previous storms
- geology
- vegetation
- amount/intensity of precipitation
- large drainage basins
What human factors affect storm hydrographs?
- deforestation
- afforestation
- agriculture
- urbanisation
How does the shape of drainage basins affect hydrographs?
- circular, more flashy
- larger drainage basins catch more precipitation
How does relief affect hydrographs?
Steep sides are flashier, water flows faster down slopes so gets to river faster
What does it mean if a flood hydrograph is flashier?
- short lag time
- high peak discharge
- steep rising/falling limb
How does high drainage density affect hydrographs?
Flashier flood, all water arrives at measuring station at the same time
What happens when the drainage basin is already saturated?
- overland flow increases as infiltration capacity has been reached
- lag time increases
- peak discharge higher
- flashy hydrograph
How does soil or rock type is impermeable?
- overland flow higher
- throughflow and infiltration reduced
- surfaces baked hard by the n
- ground frozen
How does vegetation affect flood hydrographs?
- intercepts precipitation
- water lost by evapotranspiration
- increases lag time and reduces peak discharge
How does amount and intensity and type of precipitation affect hydrographs?
- increase discharge
- snow increases lag time because it takes time to melt
How does deforestation affect flood hydrographs?
- reduces interception
- lack of roots reduces the infiltration rate into the soil
- leaves soil to greater rates of erosion which leads to sedimentation of the channel, which reduces bankfull capacity
How does afforestation affect hydrographs?
- flood prevention measure
- increases infiltration and interception
How does agriculture affect flood hydrographs?
- terracing and hillsides subdues hydrographs as stops movement of water
- grass crops increase infiltration, subdue hydrographs
- ploughing topsoils, increases infiltration
- furrows in fields that take water into river increasing discharge
How does growth or urban areas affect flood hydrographs?
- impermeable surfaces
- settlements built on floodplains
- settlements designed to transfer water as quickly as possible away from human activity to nearest river
How does localised deforestation work?
-before deforestation - high precipitation - high evapotranspiration - high infiltration - decreases water in river - after deforestation - high precipitation - low evapotranspiration (no trees) - more overland flow -flooding
How does extensive deforestation work?
Positive feedback occurs - as evapotranspiration is low -less precipitation - less overland flow-decreasing river level
What is soil drainage?
Where excess water is removed from soil profile
How is soil drainage carried out?
By network of perforated tubes (tiles)
How far deep are the perforated tubes installed?
60-120mm
Explain how soil drainage happens
When water table in soil is higher than tile, water flows into tubing through holes in plastic tubes or cracks in tiles.
The water is then drained over several days out of the field
What are the positives of soil drainage?
- build up of improved soil structure
- improved aeration
- animals can graze land
- machinery can work on land
How does improved soil structure affect farming?
- soil becomes more frable and easier to work
- greater root penetration (travel faster and further)
How does improved aeration affect farming?
- microorganisms can thrive, more humus
- provides supply of air for respiration
- plant nutrients are broken down into available form
- increased ease with soil can be warmed, improving germination
What is humus?
Dark, organic material that forms in soil when plant and animal matter decays
Why can animals and machinery go on farmland that has been drained of water?
No compaction - less overland flow
What are disadvantages of soil drainage?
- wind erosion to dry topsoil
- increases flooding in other areas
- nitrate loss
What does nitrate loss lead to?
Eutrophication
How can you minimise effects of soil drainage?
Controlled drainage - keep water table high during off season
Why would farmers want to keep the water table high during off seasons?
- increases rate of denitrification
- reduces nitrate loss to environment
What is denitrification
Process that converts nitrate to harmless nitrogen gas as soon as saturated soil warms up in spring
What is eutrophication?
Water drained from fields goes into local ponds, this causes algae and plants to grow to fast, which disturbs balance of organisms
What human practises impact the water cycle?
- deforestation
- water abstraction
- soil drainage
How does magnitude of water change over space?
- hadley cell
- frontal rainfall
How does the Hadley cell affect the magnitude water over space?
1) Equator is hot so evaporation occurs.
2) Condenses at dew point, precipitation therefore occurs above the Equator.
3) At Tropopause, air is pushed towards the tropics
4) Air becomes denser, sinking over the Tropics
5) As the cool air sinks it is met by the warm air
6) Condensation cannot occur so less precipitation over the tropics
7) Trade winds push warm air back to equator (ITCZ)
8) The air can go towards the poles,
9) Warm air meets cold and rises and condenses
10) The water vapour condenses and falls as rain, this is why Britain receives lots of rain at 60 degrees north
How does magnitude of water change over time?
- seasonal shifts of ITCZ
- geological time periods
How does frontal rainfall affect water over space?
1) Rain bearing wind approaches coastal areas of high relief
2) Air travels up the windward side
3) As the air is forced higher by the shape of the land it cools and the water vapour condenses.
4) Leading to orographic rainfall
5) When the air goes down the other side of the orographic landscape it sinks and warms, leaving a rain shadow
What is orographic rainfall?
Rainfall over high relief, mountains
How does seasonal shifts of the ITCZ affect water over time?
During the summer the ITCZ moves north over the northern hemisphere where the earth tilts 23 degrees and south during winter
How does different geological time periods affect water over time?
In the Quaternary Period sea levels were 120 m lower than they are currently. Ice covered large areas on the continents.
When are there problems with water abstraction?
Demand for water exceeds the amount available during a certain period
Where does water abstraction mainly occur?
- low rainfall
- high population density
- intensive agriculture
- industrial activity
What effects are there of water abstraction?
- sinking water tables
- empty wells
- higher pumping costs
What is the saline intrusion?
Demands for tourist along Mediterranean coastline have major over-abstraction
What is the main reason for water abstraction?
Irrigation (crops)
What river case study did we do?
River Exe
How long is river Exe?
82.7 km
What is the relief of river Exe?
- -land higher in north (514m above seas level)
- flatter in south (26m above sea level)
What % of the surface is impermeable in river Exe?
84.4%
What is the land use of Exmoor?
- 67% grassland
- 15% woodland
- 3% moorland and peat bogs
- arable farmland
What is the run-off of river Exe?
844mm
65%
