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What is mass balance in the global water system?
It’s the fixed amount of water globally – water can neither be gained nor lost
What is a store in the water cycle?
A place where water is held
What is a flow in the water cycle?
The movement of water between stores
Is the global water cycle open or closed?
Closed – no water is lost to or gained from outside the system
Name the Earth’s subsystems related to the water cycle
Hydrosphere
What is the cryosphere?
Parts of the Earth where water is solid
What are Milankovitch cycles?
Orbital changes influencing Earth’s climate over long timescales
Eccentricity
The change in the shape of Earth’s orbit from circular to elliptical over 100
Tilt
The variation of Earth’s axial tilt between 22° and 24.5° over 41
Precession
A wobble in Earth’s rotational axis over a 22
Is a drainage basin an open or closed system?
Open – water can enter and leave
What is throughfall?
Rain dripping from vegetation onto the ground
What is stemflow?
Rain running down stems and trunks to the ground
What is infiltration?
The process of water entering the soil
What is percolation?
Water moving from soil to bedrock
What is groundwater flow?
Water movement through rocks beneath the soil
What is overland flow?
Water moving across the ground surface
What is infiltration-excess overland flow?
Rainfall exceeds infiltration capacity of soil
What is saturation-excess overland flow?
Soil becomes saturated
What is channel flow?
Water moving in rivers and streams
What is interception?
Rainwater held on leaves and plant surfaces
What is soil moisture storage?
Water held in the pores of soil
What is channel discharge?
The amount of water leaving via a river over time
What is evaporation?
The change of water from liquid to gas
What is transpiration?
Water vapor released from plant stomata
What is a river regime?
The annual pattern of discharge in a river
What is a simple regime?
A river with one seasonal discharge peak
What is a complex regime?
A river with many tributaries and multiple peaks
What is discharge?
The volume of water (m³/s) passing a given point in a river
What is a storm hydrograph?
A graph showing a river's response to a rainfall event
What is peak discharge?
The maximum rate of river flow during a storm
What is peak rainfall?
The maximum rainfall recorded during a storm
What is the rising limb?
The section of a hydrograph where discharge increases
What is lag time?
The time between peak rainfall and peak discharge
What is the falling limb?
The section of a hydrograph where discharge decreases
What is preceding discharge?
The rate of river flow prior to the storm event
What is bankfull discharge?
The maximum discharge before flooding occurs
What is base flow?
The normal day-to-day flow of a river
How do antecedent conditions affect hydrographs?
Saturated soils cause faster runoff and flashier hydrographs
How does vegetation affect hydrographs?
More vegetation increases interception and evapotranspiration
How does rock type affect hydrographs?
Permeable rocks allow more infiltration and reduce runoff
How does soil depth and type affect hydrographs?
Deeper clay soils increase runoff
How does land use affect hydrographs?
Urban and agricultural land use can increase or decrease runoff and infiltration
How does basin shape affect hydrographs?
Circular basins cause faster drainage and flashier hydrographs
How does drainage density affect hydrographs?
Higher drainage density = faster flow and shorter lag times
How does slope angle affect hydrographs?
Steeper slopes = less infiltration and more surface runoff
What is convectional rainfall?
Rain caused by surface heating leading to rising and cooling air
What is frontal rainfall?
Rain caused when warm and cold air masses meet
What is orographic rainfall?
Rain caused when moist air is forced over mountains
What is the feeder-seeder mechanism?
Raindrops fall from high clouds and grow by collecting droplets from lower clouds
What is the Bergeron-Findeisen process?
Ice crystals in high clouds grow
What is the collision process?
Larger raindrops collide and merge with smaller droplets to grow in size
What is runoff?
Rainwater movement via overland flow
What is the effect of snowmelt and ice ablation?
Increases runoff into rivers
What is the effect of storm activity on runoff?
Intense or prolonged rainfall leads to excess runoff and possible flooding
How does urbanisation affect runoff?
Increases impermeable surfaces
What is the water balance equation?
P = Q + ET + ΔS
What causes a water deficit?
When precipitation is less than the sum of evapotranspiration and runoff
What causes soil moisture surplus?
High winter precipitation and low evaporation rates
What causes soil moisture deficit?
High summer temperatures and plant use of soil water
What is a meteorological drought?
A prolonged period of below-average rainfall
What is an agricultural drought?
Insufficient soil moisture for crop production
What is a hydrological drought?
Low water reserves in lakes
What is an aquifer?
A permeable rock layer that stores extractable groundwater
What is an artesian aquifer?
An aquifer confined between impermeable layers under pressure
What is the Aral Sea disaster?
A shrinking inland sea due to overuse for irrigation
What is the carbon cycle?
The movement of carbon through the Earth’s atmosphere
What percentage of Earth’s carbon is atmospheric?
Only 0.001%
What percentage of carbon is in living organisms?
0.004%
Where is most carbon stored?
In sedimentary rock and fossil fuels (99.9%)
What is a carbon sink?
A store that absorbs more carbon than it releases
What is a carbon source?
A store that releases more carbon than it absorbs
What is carbon sequestration?
The natural capture and storage of CO₂ from the atmosphere
What is photosynthesis?
Plants and phytoplankton fix atmospheric CO₂ into carbohydrates
What is respiration?
Organisms release CO₂ through breaking down glucose
What is decomposition?
The breakdown of organic matter releasing carbon through physical
What is combustion?
Burning organic material or fossil fuels
What is the physical (inorganic) carbon pump?
CO₂ dissolves in ocean surface and is transported to deeper layers
What is the biological carbon pump?
Phytoplankton absorb CO₂ and pass it through marine food chains
What is the carbonate pump?
Plankton use CO₂ to create shells
What is carbonation?
Chemical weathering where CO₂ dissolves in rainwater and reacts with rock
How is carbon released from rock?
Through volcanic activity
Where is carbon stored in biomes?
In biomass
What is a biome?
A major ecosystem type like a rainforest or tundra
How much carbon is in tropical rainforests?
550 GtC in biomass and soil
How much carbon is in temperate grasslands?
185 GtC in biomass and soil
How does deforestation affect carbon?
Reduces storage and increases atmospheric CO₂
What is afforestation?
Planting trees to increase carbon sequestration
How does agriculture affect carbon?
Soil erosion and vegetation loss reduce carbon storage
What is peat?
Partially decomposed vegetation in waterlogged anaerobic soil
Why is peat a carbon sink?
It accumulates plant material faster than it decomposes
Where are peatlands found?
In high rainfall upland areas like Scotland
How much land is peatland?
3% of Earth’s land surface stores 60 billion tonnes of carbon
What degrades peatlands?
Drainage
What is the effect of degraded peatlands?
They become carbon sources rather than sinks
What is peat restoration?
Rewetting and revegetation to restore carbon storage
What is desertification?
The degradation of land due to climate change or poor land use
How does desertification affect water and carbon cycles?
Reduces infiltration
What is NPP?
Net Primary Productivity – the rate of plant growth storing carbon
How does humus help?
It stores carbon and retains up to 90% of its weight in water