Water cycle units 1-3 practice Flashcards
State the main input to a drainage basin
Precipitation
State the three main outputs of a drainage basin
Evaporation
Transpiration
River flow (run-off) into Ocean
State the three main flows in a drainage basin
River flow
Percolation
Vapour Transport
State the two stores in a drainage basin
Groundwater
Soil
What’s the difference between an open and closed system?
Open system: a system in which the quantity of matter will vary over time
Closed system: a system in which the quantity of matter is fixed
Why is a drainage basin an open system?
the quantity of water will fluctuate over time due to variations in the quantity of inputs and outputs.
Why is the global water cycle a closed system?
the quantity of water is fixed as no water leaves the planet and no new water is created
On a global scale, what’s the fixed amount of water present?
1.4 billion km3
What percentage of the global water is stored in oceans?
97%
what percentage of global water is stored in the cryosphere?
2%
what percentage of global water is stored in groundwater?
1%
What’s the link between the cryosphere and ocean store?
As rates of accumulation and rates of ablation increase within the cryosphere, runoff causes the store of water in the oceans to increase
What two factors causes sea level fluctuations on a short timescale of years?
Seasonal changes in snow fall and ice formation
Variations in global temperature from year to year ( volcanic eruptions, El Nino events – this will be covered later in the course)
State the change in size of stores over space and time
Increase in Cryosphere store:
- ice sheet extended across Scandinavia, North Sea and northern Britain. Thickness of ice exceeded 2500m over Scandinavia. Smaller Ice Caps covered Iceland, the Alps and Pyrenees mountains.
- increase in sea ice which extended through large area of the North Atlantic as far south as Ireland.
Reduction in Ocean store:
- Due to quantities of water stored in the cryosphere, sea levels around Europe were over 100m lower than present day
Define a simple river regime
one in which there is a clear seasonal difference between a period of high water levels and a period of low water levels
Define a complex river regime
one in which the pattern of discharge has multiple peaks and more variable flow
State the climate factors influencing river regime characteristics
Annual variation of precipitation quantity: this will determine the amount of water entering the drainage basin
Annual variation of precipitation type: this will determine if the precipitation enters a river
Annual variation in levels of evapotranspiration: this will determine the level of an important output from the drainage basin
Annual variation in temperature: this will determine not only evaporation but also if and when water is in a frozen state
State the human factors influencing river regime characteristics
Dam construction: this will control the level of channel flow downstream of the dam
Land Use Change: Changes in the levels of interception, infiltration, surface run-off, base flow etc. could occur if land use change takes place in a drainage basin. This will determine the amount and rate at which precipitation can become channel flow.
Define lag time
The period between maximum precipitation and peak discharge
Define rising limb
The rising portion of the hydrograph showing increased levels of discharge
Define peak discharge
The point in time where the river reaches its highest level
Define bankful discharge
When the level of discharge is at the channel capacity and any further increase in discharge will result in flooding.
Define the falling limb
The period where discharge is decreasing and the level of the river is falling
Define baseflow
The portion of discharge fed from groundwater flow
State the climatic factors influencing a storm hydrograph
Precipitation type, amount, duration and intensity, temperature, evaporation, transpiration and antecedent conditions
Define antecedent conditions
wet conditions before a storm that cause the ground to become saturated
How does an elongated drainage basin affect hydrographs?
they have lower peak discharge as water at the head of the basin take longer to reach the river mouth than water close to it
How does a circular drainage basin affect hydrographs?
water takes less time to reach the river as all points in the drainage basin are roughly equidistant from the river so all precipitation reaches the river at the same time resulting in a high peak discharge
What do basins with lots of streams and rivers do to the lag time?
basins with lots of streams and rivers have a short lag time and fairly steep falling limb because water drains out of them quickly
How does the gradient of slopes affect hydrograph?
basins with steep slopes will have a high peak discharge and short lag time because the water can travel faster downhill
Define drainage basin
the catchment area drained by a single river and its tributaries
Define throughfall
Water dripping off vegetation to the ground surface
Define stemflow
water flowing over leaves, stems and branches
define infiltration
movement of water from the ground surface into the soil
define overland flow
the flow of water over the ground surface
define throughflow
horizontal movement of water downslope through soil
define percolation
vertical downward movement of water through the soil to the groundwater
define channel flow
water flowing within a river
Name the six types of stores
interception store, vegetation store, surface store, soil moisture store, channel store, groundwater store
Name the three main river outputs
evaporation, transpiration and channel discharge to oceans
How does precipitation form in one sentence (don’t state the conditions)?
Precipitation forms in the atmosphere when water vapour condenses.
Name the first condition required for precipitation to form (hint condensation nuclei)
A small particle (typically dust or sea salt) in the atmosphere around which condensation takes place. These particles are known as condensation nuclei.
Name the second condition after condensation nuclei required for precipitation to form
Cooling of the air below the dew point. The temperature at which condensation occurs is called the dew point and is dependant on the humidity of the air.
Define lapse rate
as altitude increases, temperature decreases. Temperature drops around 1 degree every 100m.
Explain orographic rainfall
Warm, moist air rises off the sea up and over mountainous regions where air cools, condensing and forming clouds. There’s no dew point because the air is unsaturated and therefore holds no moisture.
Where does orographic rainfall affect?
Occurs in areas of the West of England e.g. Breckon Beacons, Dartmoor, Exmoor. In these locations, annual precipitation exceeds 2000mm annually.
Explain convectional rainfall
occurs when the energy from the sun heats up the earts surface causing water to vaporise. The warm, moist air rises, cools and reached the dew point resulting in condensation and water vapour turning into a liquid. This leads to large cumulonimbi’s clouds.
Which areas are affected by convectional rainfall?
Equatorial regions including tropical rainforests. Also the UK on warm summer days.
Explain frontal rainfall
When two air masses of contrasting temperature and density meet, they create a front separating the contrasting air masses. Colder air is more dense, forcing the warm air up. t cools and reached the dew point, condensing turning water vapour into liquid leading to frontal rain.
Which areas are affected by frontal rain?
UK due to its latitude. Warm tropical air collides with colder polar air along the Polar Front.
State the two theories for precipitation formation
Bergeron-Findeisen theory of ice crystal growth and the collision mechanism
Explain the Bergeron-Findeisen process (3 steps)
Occurs in clouds where temperatures are just below 0 degrees - in higher latitudes and altitudes
Water vapour droplets are supercooled but stay as liquid below the normal freezing point. They only freeze on contact with a condensation nuclei.
Dust particles act as a condensation nuclei allowing a droplet to freeze. Upon contact with the supercooled droplets these will also freeze, thus enabling hexagonal ice crystals.
Explain Collision Theory (4 steps)
This theory explain the formation of rain in the warm tropics where cloud temperatures are too warm for ice crystals to form.
Super-sized condensation nuclei e.g. large sea salt particles provide seeds around which very large water droplets form
The larger super droplets fall and collide wit smaller droplets, absorbing them
This mechanism is associated with convectional rainfall resulting in heavy downpours and flash flooding from infiltration-excess overland flow or Hortonian Flow.
State the four physical factors which cause excess runoff
Prolonged rainfall (Feb 2020 UK)
Intense storms (Boscastle)
snowmelt (Red River of Fargo)
monsoon rain
State the two human factors which cause excess runoff
Changing land use e.g. urbanisation
Mismanagement of land e.g. deforestation
Define a water deficit
when an area lacks sufficient water to meet its needs
What are meteorological droughts caused by
Meteorological droughts are caused by variations in the normal atmospheric pressure systems
For meteorological droughts, state what atmospheric pressure is in two points
Where warm air rises this is Low Pressure. Where Cold is descends, this is high pressure.
How is a drought linked to meteorological causes of a water deficit?
a drought is linked extended periods of high pressure over a region
State the two meteorological causes of a water deficit
seasonal variations (1976 UK drought) and long term climate change (megadrought)
State the two human causes of a water deficit
depleting aquifers (potato farming Egypt) (California central valley for depletion and management) and surface water resources by extraction (Aral sea)
State the two ways of addressing an aquifer water deficit
Natural and artificial recharge of aquifers
Define artificial recharge
Involves capturing excess runoff during periods of heavy rain and diverting water into recharge basins or canals. These basis have porous bases that allow the captured water to percolate down into the aquifer.
What’s natural ground water recharge (London Basin)?
aquifers can be recharged naturally over time through rain, river bed seepage, flooding and other natural processes including snow melt.
When will a water table rise?
When the rate of percolation is greater than the rate of groundwater flow the water table will rise.
