1.3 The water cycle and water insecurity Flashcards
What % of the world’s water do oceans store?
97%
What % of the world’s water is freshwater?
2.5%
Of the freshwater, what % is stored in glaciers, ice caps, and ice sheets?
69%
Of the freshwater, what % is stored as ground water?
30%
Of the freshwater, what % is surface and other freshwater sources?
1%
What are other surface and freshwater stores made up of?
permafrost, lakes, swamps, marshes, rivers and living organisms.
Define blue water
water stored in lakes, rivers, streams, and ground water, in liquid form
Define green water
water stored in soil and vegetation
Define grey water
waste bath, sink, and washing water
Describe the hydrology in polar regions (6)
▪ 85% of solar radiation is reflected
▪ Permafrost creates impermeable surfaces
▪ Lakes and rivers freeze
▪ Rapid runoff in spring
▪ Seasonal release of biogenic gases into atmosphere
▪ Orographic and frontal precipitation
Describe the hydrology in tropical rainforests (6)
▪ Dense vegetation consuming 75% of precipitation
▪ There is limited infiltration
▪ Deforestation leads to less evapotranspiration and precipitation
▪ Very high temperatures
▪ Very humid
▪ Convectional rainfall
Describe the Inter-Tropical Continental Zone (ITCZ)
- The Earth consist of six cells of circulating air, which form the globe’s climate control
- There are 3 in the northern hemisphere, and 3 in the opposite direction in the southern hemisphere
Define drainage basin
- A drainage basin is an open subsystem operating within the closed global hydrological cycle.
- an area of land drained by a river and its tributaries with a boundary (known as the watershed), usually composing of hills and mountains. `
Define drainage basin
- A drainage basin is an open subsystem operating within the closed global hydrological cycle.
- It’s defined as an area of land drained by a river and its tributaries with a boundary (known as the watershed), usually composing of hills and mountains.
is the water cycle an open or closed system?
- On a local scale, the water cycle is an open system
- on a global scale, the water cycle a closed systems
What is the main input into a drainage basin?
precipitation
Cause of precipitation
Precipitation is caused by the cooling and condensation of water moisture in the atmosphere, forming clouds that release moisture in the form of rain, snow, hail, sleet, etc.
Factors affecting volume or condition of precipitation (3)
- seasonality
- climate variability
- latititude
How does seasonality affect precipitation?
- In some climates (such as monsoon and Mediterranean) there are strong seasonal patterns of rainfall.
- Therefore the time of year determines the precipitation input within the drainage basin
How does climate variability affect precipitation?
- sudden or long term changes to the climate can happen, which would affect precipitation levels and so the drainage basin as a whole.
→ Secular Variability – long term (for example as a result of climate change trends)
→ Periodic Variability – annual, seasonal or monthly context
→ Stochastic Variability – random factors like localisation of thunderstorm
How does latitude affect precipitation?
- The location of the drainage basin has a major impact on climate, and so the volume and type of precipitation falling.
- In most cases, the higher the latitude from the Equator, the colder the climate, and so snowfall occurs more often than rainfall.
- Also, at latitudes where air cells converge (ITCZ), the climate will be categorised by the rise or fall of air
Name the three types of rainfall
- convectional
- frontal/cyclonic
- relief/orographic
Describe convectional rainfall
- Often a daily occurance.
- The morning heat warms the ground, which in turn heats low-level moisture (from plant dew or surface stores).
- This moisture evaporates and rises.
- As the air rises, it cools and the moisture within will condense, to form rain and in turn (as more moisture accumulates) rainfall.
- In tropical climates, convectional rainfall is most common; within tropical rainforests, rainfall occurs mid-morning before the temperature rises too high for condensation to occur.
Describe frontal/cyclonic rainfall
- Where two air masses meet, a wedge can occur of hot air within cold air - this is called a depression.
- At the front (were the two air masses meet), warm moist air is forced to rise above the cold air mass, causing the water moisture within to cool and condense, to form cyclonic precipitation.
- Depressions are very common to the UK - approx 100 depressions hit the UK each year.
Describe relief/orographic rainfall
- When warm, moist air (often travelling onto land from sea) meets land of high relief (e.g. hills), the air mass is forced to rise above the hill to continue travelling.
- As it rises, the air mass cools and the moisture within condenses, to form clouds and rainfall.
- Orographic rainfall depends on the relief and location of the land immediate after the sea - many coastal landscapes are too cold, low lying or hills are set too far inland for relief rainfall to occur
- causes rain shadow on other side of high land
Define discharge
the volume of water passing a certain point in the channel over a certain amount of time
Name the flows within a drainage basin (6)
- interception
- infiltration
- surface runoff
- throughflow
- percolation
- groundwater
How does relief affect basin flows?
There are many flows within the drainage basin, many due to gravity and so depend on the relief of the land
Describe interception
- Interception is the direct intervention of plants’ leaves in changing the direction or temporarily stopping precipitation as it falls to the surface.
- Any moisture retained by the surface of the leaf (interception store) is generally greatest at the start of storms.
- A plant’s interception capacity varies depending on the type of vegetation.
Describe infliltration
The movement of water from the surface into the soil
Define infiltration capacity
The infiltration capacity is the maximum rate at which water can be absorbed by the soil
Factors affecting infiltration capacity (5)
▪ Soil Composition – Sandy soils have higher infiltration rates compared to clay.
▪ Previous precipitation - The saturation of soils will reduce infiltration rates, hence surface runoff increases after long, intense periods of rainfall.
▪ Type and amount of vegetation - dense root growth can inhibit the infiltration of water, and interception of plants’ leaves will delay infiltration
▪ Compaction of soils will reduce the infiltration rate.
▪ Relief of land – sloped land will encourage more runoff, therefore less infiltration as a direct result
Describe surface runoff
- Water flows overland, rather than permeating deeper levels of the ground.
- Overland flow occurs faster where the gradient of land is greater.
- Surface runoff if the primary transfer of water to river channels, hence heavily influencing their discharge
- Moderate/Fast rate of water transfer
Describe throughflow
- Water moves laterally through the soil and into streams or rivers.
- Speed of flow is dependent on the type of soil
- Clay soils with a high field capacity and smaller pore spaces have a slower flow rate
- Sandy soils drain quickly because they have a lower field capacity, larger pore spaces and natural channels from animals such as worms.
- Moderate/Fast rate of water transfer
Describe percolation
- Water moves from the ground or soil into porous rock or rock fractures (deeper bedrock and aquifers).
- The percolation rate is dependent on the fractures that may be present in the rock and the permeability of the rock
- Slow rate of water transfer
Describe groundwater flow
- The gradual transfer of water through porous rock, under the influence of gravity.
- Water can sometimes become trapped within these deeper layers of bedrock, creating aquifers and long water stores for the drainage basin
- Slow rate of water transfer
Outputs of the drainage basin (2)
- evaporation
- transpiration
Describe evaporation
This is the direct loss of water moisture from the surface of a body of water, the soil and interception storage (on top of leaves) to the atmosphere
Factors increasing evaporation rate (4)
- Evaporation rates increase when the weather is warmer, windier and dryer.
- Volume and surface area of the water body - the larger the surface area, the faster the rate of evaporation.
- Vegetation cover or built environment surrounding the water - anything that reduces direct sunlight to the water body will reduce evaporation.
- The colour of the surface beneath the water - black tarmac will absorb heat faster than white snow, and so evaporation will occur faster on the tarmac
Describe transpiration
This is a biological process where water is lost to the atmosphere through the pores of plants (stomata)
Factors affecting transpiration rates (4)
- seasonality
- type of vegetation
- moisture content of the air
- time of day
Stores of water (5)
- soil water (mid-term)
- groundwater (long-term)
- river channel (short-term)
- interception (short-term)
- surface water (variable)
Define cryosphere
areas of the earth where water is frozen into snow or ice
Define fluxes
the rate of flow between the stores
Define residence time
the average time a water molecule will spend in a store
Define water table
The water table is the upper level at which the pore spaces and fractures in the ground become saturated.
Physical factors affecting the drainage basin (6)
- climate
- soil composition
- geology
- relief
- vegetation
- size
How does climate affect a drainage basin?
influences amount of rainfall and vegetation growth.
How does soil composition affect a drainage basin?
influences rate of infiltration and throughflow.
How does geology affect a drainage basin?
- affects percolation and groundwater flow
- permeability of rock, angle of strata
How does relief affect a drainage basin?
steeper gradients of land will encourage faster rates of surface runoff
How does vegetation affect a drainage basin?
- affects interception, overland flow
- as vegetation becomes wetter, interception effectiveness decreases
- vegetation type and cover affect interception rate
How does size affect a drainage basin?
larger basins collect more precipitation generally
Human factors affecting drainage basins (8)
- cloud seeding
- deforestation
- afforestation
- dam construction
- change in land use
- ground water abstraction
- irrigation
- urbanisation
Describe cloud seeding
- silver iodide released by a plane or ground based generator
- silver iodide particles reach the targeted cloud
- silver iodide aids in the formation of ice crystals
- ice crystals become large enough to fall and create snow
How does deforestation affect a drainage basin?
Less vegetation means less interception, less infiltration, more overland flow, leading to more flooding, cycle speeds up
How does afforestation affect a drainage basin?
More vegetation means interception, less overland flow, more evapotranspiration
How does dam construction affect a drainage basin?
Dams reduce downstream river flow and discharge, increase surface stores so more evaporation