3.1.1.2 The water cycle Flashcards
Description of the lithosphere
- surface water, including biological and groundwater
- Finland and Canada have the most lakes
Description of the hydrosphere
- oceans cover 70% of the earth’s surface
- contains 97% of water
- saline
Description of the cryosphere
- water held in ice
- if ice sheets melted, sea levels would rise by 60m
Description of atmosphere
- commonly water vapour
- warm air holds more vapour than cold air
- increase in water vapour leads to an increase in temperatures (positive feedback)
- absorbs and reflects solar radiation
Name the 5 factors driving the change in water stores
- evaporation
- condensation
- cloud formation
- precipitation
- cryospheric processes
What do the rates of evaporation depend upon
- amount of solar energy
- the availability of water
- humidity of the air (the more humid the air, the less evaporation)
- temperature of the air (warmer air can hold more water)
Define relative humidity
The amount of water vapour in the air compared to how much it could possibly hold at that temperature.
How could condensation occur
- air is cooled
- there is a fall in pressure
What does cloud formation require
A condensation nuclei
Define dew point
The point where the air is at maximum saturation
What are the two main causes of precipitation
- air temperature is reduced to dew point
- volume of air increases as it rises, without an increase in temperature (adiabatic cooling)
Define orographic rainfall
Air is forced to rise over hills/ mountains
Define convectional rainfall
Warm air rises away from surfaces and cools
Define frontal rainfall
Air masses of different temperatures meet and the warm air rises
Define accumulation
Inputs of a glacial system due to snowfall compressing into glacial ice
Define ablation
Outputs of a glacial system due to melting
Define sublimation
Ice changing directly into water vapour
What is a drainage basin
An area of land drained by a river and its tributaries
What is the name of the boundary of a drainage basin
Watershed
Define evapotranspiration
Combined loss of water through evaporation and transpiration
Define runoff
The output of water from the drainage basin system as it moves across the surface
Define interception as a store
A short term storm where vegetation can hold precipitation on leaves and branches
Define surface storage
Puddles
Generally more common in built environments where there is less infiltration
Define soil water storage
Pore spaces between soil particles fill with water
What percentage of sand is pore spaces
20-45%
What percentage of clay is pore spaces
40-60%
Define groundwater storage
Water stores underground in permeable and porous rocks
Define channel store
The volume of water in a river channel
Define stemflow
Water flowing down the stems of plants and trees
Define infiltration
Water which soaks into the soils
Define overland flow
Rainfall which flows over the ground because the soil is saturated or because rainfall exceeds infiltration capacity
Define channel flow
The flow of water in rivers
Define throughfall
Water moving from vegetation to the ground
Define throughflow
The lateral movement of water down a slope to a river channel
Define percolation
Downward movement of water to underground stores
Define groundwater flow
Slow movement of water within saturated rock
Factors affecting infiltration rate
- increased vegetation means an increased rate (roots)
- the gradient of hill slopes (topography)
- the flow supply
Main factor affecting soil storage
Type of soil (sand or clay)
Factors affecting interception rates
- type of vegetation (coniferous intercepts 35% precipitation whereas deciduous intercepts 25% annually)
- plant density
- precipitation intensity
Define the water balance
The long term balance between the inputs and outputs of a drainage basin system
Define positive water balance
Precipitation exceeds evapotranspiration
How do seasonal changes affect the water balance
- In winter, the increased precipitation may lead to a soil moisture surplus and increased runoff
- In summer, utilisation of water by humans and vegetation may be high and there could be a soil moisture defecit
What measures river flow
Discharge
How do drainage basin characteristics affect the flood hydrograph
Larger drainage basins catch more precipitation meaning a large peak discharge, however this discharge must travel further so there is a lower lag time.
Opposite for small drainage basins
How does the amount of water already present in the drainage basin (antecedent moisture) affect lag time.
If the soil is already saturated, there will be more surface runoff (the fastest flow) therefore there will be a shorter lag time.
How does rock type affect the flood hydrograph
Impermeable rock reduces infiltration, increases surface runoff, reducing lag time.
Peak discharge increases as more water reaches the river faster
Human factors on the storm hydrograph
- Impermeable surfaces increases runoff
- Man made drainage systems also reduce lag time
How do storm events change the water cycle over time
During a storm event there is less infiltration, more surface runoff and therefore more flooding
How do seasonal events change the water cycle over time
- wet seasons have a water surplus
- dry seasons have a water deficit (link to water balance)
How do farming practices change the water cycle over time
- huge quantities of water are used in food production which redistributes water away from natural pathways
- farmers dig ditches to avoid waterlogging plants which increases overland flow
- depleted groundwater stores to be used for irrigation
How does water abstraction change the water cycle over time
- the process of taking water from a ground source
- can cause rivers to dry up and damage to wetland environments
- salt water intrusion in coastal areas
How does Israel combat against abstraction
- 86% water reuse
- 600,000m^3 per day desalination plant
How does deforestation change the water cycle over time
- lowers evapotranspiration and interception
- increases overland flow and throughflow as vegetation usually slows down these processes
- increased discharge and increased risk of flooding
