1. Water cycle processes/stores Flashcards
What are the three main stores of the global water cycle?
The atmosphere, oceans, and land
What is the biggest and smallest store of water?
Biggest = oceans 1,370,000 (km3 x 10^3) Smallest = atmosphere 13 (km3 x 10^3)
Describe the oceanic store of water:
Five oceanic bodies and several smaller seas
Biggest is Pacific
Describe the atmospheric store of water:
Held as water vapour and absorbs and reflects incoming solar radiation
Warm air holds more vapour than cold air
Describe the ‘land’ store of water:
Cryospheric = sea ice, ice caps, ice sheets, Alpine glaciers, and permafrost – high altitudes and latitude Terrestrial = rivers (Amazon), lakes (Canada) wetland, groundwater
What processes are involved in the water cycle x5?
Precipitation Evapotranspiration Condensation Run-off Groundwater flow
Define precipitation:
Moisture falling from clouds towards the ground (rain, snow, hail)
Define evapotranspiration:
Combined loss of water at the surface through evaporation and transpiration (evaporation of moisture from pores on the leaf surfaces) of plants
Define run-off:
The movement of water across the land surface
Describe groundwater flow:
The horizontal movement of water within aquifers
What are the 3 biggest global reservoirs of water on Earth?
- Oceans 1,370,000 (km3 x 10^3) = 97% of global water
- Polar ice/glaciers 2900 (km3 x 10^3) = 2% of global water
- Groundwater 9,500 (km3 x 10^3) = 0.7% of global water
How much freshwater is stored in ice caps of Antarctica and Greenland?
Three-quarters
How much freshwater is stored below ground in permeable rocks?
One-fifth
What is the average time a water molecule spends in the atmosphere?
Just 9 days
What is the water cycle budget?
The annual volume of movement of water by flows (precipitation, evapotranspiration, run-off etc) between stores (oceans, permeable rocks etc)
How much water does the water cycle budget circulate per year?
505,000km^3 – USGS
What are the inputs of water into the atmosphere?
Evapotranspiration
Water vapour evaporated from oceans, soils, lakes
Vapour transpired through leaves
What are the outputs of water from the atmosphere?
Precipitation eg rain
Condensation eg fog
How does run-off accumulate?
Precipitation drains from the land into rivers – most water does this once it has infiltrated the soil
Water under gravity percolates into aquifers which eventually reach the surface as springs and contributes to run-off
What is groundwater?
Water stored underground in permeable rocks known as aquifers
What is infiltration?
The vertical movement of rainwater through the soil
What is percolation?
The movement of surface and soil water into underlying permeable rocks
What is the water balance equation?
Precipitation = evaporation + streamflow +/-storage
Positive water balance: precipitation exceeds evapotranspiration
Negative water balance: evapotranspiration exceeds precipitation
What are the principle flows in the water cycle that link the various stores?
Precipitation, evaporation, transpiration, catchment hydrology (run-off, infiltration, percolation, and through-flow) and cryospheric processes
What are the various forms of precipitation?
Rain, snow, hail, sleet, and drizzle
How does precipitation form?
- Forms when vapour in the atmosphere cools to its dew point and condenses into tiny water droplets or ice particles to form clouds
- The tiny droplets aggregate, reaching a critical size, and leave the cloud as precipitation
What are the three types of rainfall?
- Orographic = air is forced to rise over mountains
- Frontal = two fronts meet; warm air rises over the cooler air
- Convectional = warm air rises from hot surfaces on a sunny day
What is the dew point?
The critical temperature at which condensation occurs
What characteristics of precipitation affect the drainage basin scale?
- Type of precipitation – in high latitudes precipitation falls as snow which causes a time lag between snowfall and runoff
- Intensity of precipitation – high intensity (10-15mm/hour) moves rapidly overland
- Duration of precipitation – prolonged events may cause river flooding
- Occurrence of precipitation – precipitation can be concentrated into a rainy season when river discharge is high eg Mediterranean
What is transpiration?
The diffusion of water vapour to the atmosphere from the leaf pores (stomata) of plants and is responsible for 10% of the moisture in the atmosphere
What factors affect transpiration?
Temperature, wind speed, humidity, water availability to plants
What is condensation?
The phase change of vapour to liquid water that occurs when air is cooled to its dew point
How do clouds form?
When the air is saturated because it has cooled below the dew point OR condensation nuclei are present
What are the 3 main types of cloud?
- Cumuliform clouds
- Stratiform clouds
- Cirrus clouds
Describe cumuliform clouds:
Form when the air is heated through contact with the Earth’s surface and causes heated air parcels to rise by convection, and expand due to a fall in pressure
As cooling reaches thew dew point, condensation begins and clouds form
Describe how stratiform clouds form:
Develop when an air mass moves horizontally across a cooler surface ie ocean through the process of advection
Describe how cirrus clouds form:
Wispy clouds form at high-altitudes and produce tiny ice crystals – do not produce precipitation
What is adiabatic expansion?
The expansion of a parcel of air due to a decrease in pressure – expansion causes cooling
When does cooling occur?
- Air is warmed by contact with ground and rises freely – adiabatic expansion occurs
- Air mass moves horizontally across a cooler surface – advection
- Air masses rise as they cross a mountain
- Warm air mixes with cooler air
What is a lapse rate?
The vertical distribution of temperature in the lower atmosphere, and the temperature changes that occur as it rises vertically away from the ground
What are the three types of lapse rates?
- Environmental lapse rate = vertical temperature profile of the lower atmosphere at any given time
- Dry adiabatic lapse rate = the rate at which a parcel of dry air cools as it rises
- Saturated adiabatic lapse rate = the rate at which a saturated parcel of air cools as it rises (SALR is lower than the DALR as condensation releases heat
Why do clouds rise?
Atmospheric instability = air parcels are warmer inside the cloud than the external atmosphere
What are cryospheric processes?
- Accumulation
- Ablation
- Sublimation
What is a drainage basin?
An area of land drained by a river and its tributaries that forms a subsystem, in particular an open system, of the water cycle
What are the inputs of a drainage basin?
Precipitation
Condensation
What are the stores in a drainage basin x5?
- Vegetation store: vegetation cover intercepts precipitation eg 58% rainfall intercepted in rainforests
- Surface storage: mainly in built environments as puddles
- Soil storage: pores between soil particles fill with water eg clay has 40-60% volume
- Groundwater store: permeable rocks
- Channel store: volume of water in a river channel
What are the flows in a drainage basin x7?
- Stemflow
- Infiltration
- Run-off (overland flow + saturated overland flow)
- Throughfall
- Throughflow
- Percolation
- Groundwater flow
Describe stemflow:
Occurs when water flows down the stems of plants
Describe infiltration:
Occurs when water soaks into the soil
Infiltration rate is affected by texture, soil structure, and organic content
Describe run-off (overland flow) + the two theories:
Rainfall flowing over the ground surface due to
- Saturated overland flow: soil become saturated and the water table rises to the surface
- Overland flow infiltration rate being exceeded
Describe throughfall:
Water moving from vegetation to the ground
Describe throughflow:
Lateral movement of water down a slope to a river channel
Describe percolation:
Downward movement of water into groundwater stores
Describe groundwater flow:
Downward and lateral movement of water within saturated rock (aquifers)
What are the outputs of a drainage basin?
Evapotranspiration
Leakage: loss from groundwater stores
Run-off: movement of water across the land surface
