water cycle Flashcards
systems
systems- a set of interrelated components working together towards some kind of process
what are systems made up of?
inputs —> matter or energy is added to the system
outputs —> matter or energy leaves the system
stores —> a part of the system where something is held for a period of time
flows —> a link between 1 store and another, along which something moves
boundaries —> the edge of the system (the line between 1 system and another)
- open system —> energy and matter enter and leave the system
- closed system —> energy can enter and leave but matter cannot enter or leave (matter can be water) —> it can only cycle between stores
- dynamic equilibrium —> inputs and outputs are equal —> no overall change to the system
positive and negative feedback loop
global water stores
global water stores:
- hydrosphere —> all the water on earth —> it may be in liquid, solid and gas form (water vapour stored in the atmosphere)
- cryosphere —> all forms of frozen water
- biosphere —> all living things e.g. plants, animals, fungi, insects and bacteria
- lithosphere —> the outermost part of the earth, including the crust and upper parts of the mantle
- atmosphere —> layer of gas surrounding the planet —> e.g. clouds
(water is moved between the stores)
distribution of water on earth:
- 97% of water is found in oceans
- only 3% of water on earth is fresh water
out of the 3% fresh water:
- only 1% of fresh water is easily accessible fresh water
- 79% of fresh water is stored in ice caps and glaciers
- 20% of fresh water is stored in groundwater
out of the 1% of easily accessible fresh water:
- 52% comes from lakes
- 38% comes from soil moisture
- 8% comes from atmospheric water vapour
- 1% comes from rivers
- 1% comes from water within living organisms
- The size of the global water stores can change slightly. The largest store (hydrosphere) has a limited change in volume over the short-term. However, if we consider longer timescales (last ice age), the volume of ocean water will decrease as more of this water is contained in the cryosphere
evaporation, condensation, cloud formation, precipitation, cyrospheric processes
- global hydrological cycle —> water is continuously cycled between different stores in a closed system
- closed system —> fixed amount of water on the planet —> water is just moved around (water changes state as it moves between stores)
- gas to liquid/ liquid to gas —> condensation/ evaporation
- solid to liquid/ liquid to solid —> melting/ freezing
- solid to gas —> sublimation
- gas to solid —> deposition
Transfers that change the size (magnitude) of the stores:
- Whilst the overall volume of water contained in the stores does not change that significantly on the global scale, transfers and flows will affect the amount of water over time that remains in a store e.g. evaporation will increase in the summer which leads to higher atmospheric storage and a drop in ocean storage
Evaporation:
- liquid to gas
- approx 90% of the atmospheric water store is from evaporation from the oceans and seas
- the magnitude of evaporation depends on temperature and supply of water e.g. low temperatures and a small supply of water —> evaporation levels will be low// high temperatures and a large supply of water —> evaporation levels will be high —> likely to occur due to climate change
- Global: effect of evaporation on global scale ocean and sea level is minimal —> the water cycle maintains a balance (evaporation and precipitation are in balance) so the magnitude of evaporation doesn’t significantly alter ocean or sea levels over short time scales. Oceans have a high heat capacity meaning they don’t heat up or cool down quickly, limiting extreme evaporation variations
- Local: in a drainage basin, evaporation has a bigger impact because the water supply is smaller and localised. These areas respond faster to temperature changes, climate changes, or human activities. If evaporation is higher than precipitation, water levels can drop —> affecting the environment and water supply
Condensation:
- gas to liquid
- condensation occurs when temperature falls and humidity (increased water vapour) increases —> in the atmosphere, water vapour molecules form around tiny particles like dust and smoke (called aerosols) —> acts as condensation nuclei —> water molecules accumulate, forming droplets —> when these droplets grow large enough, they become visible as mist, fog, or clouds —> condensed water droplets may eventually fall to earth as precipitation
Cloud formation:
how do clouds form?
- condensation occurs when temperature falls and humidity (increased water vapour) increases —> in the atmosphere, water vapour molecules form around tiny particles like dust and smoke (called aerosols) —> acts as condensation nuclei —> water molecules accumulate, forming droplets —> when these droplets grow large enough, they become visible as mist, fog, or clouds —> condensed water droplets may eventually fall to earth as precipitation
Precipitation:
what causes rain?
- other air masses —> warm air is less dense than cool air —> when they meet, the warm air is forced to rise —> air cools and condenses to form clouds —> frontal precipitation
- topography —> when warm air meets mountains, it is forced to rise —> air cools and condenses to form clouds —> orographic precipitation e.g. the pennines
- convection —> sun heats up the ground —> moist air rises —> air cools and condenses to form clouds —> convective precipitation
Reasons for differing rainfall patterns:
The Equator (Hot and Rainy)
- Curvature of the earth —> affects patterns of evaporation, condensation, and precipitation —> more solar radiation is received and absorbed near the equator than at the poles —> the suns rays strike the earth most directly near the equator —> causing higher temperatures and increased evaporation —> as the hot air rises and cools, condensation occurs and forms clouds —> leading to heavy rainfall
Subtropics (Dry and Desert-Like)
- After the air rises at the equator, it moves away, cools down, and sinks around 30° north and south of the equator
- When air sinks, it prevents clouds and rain from forming, making these areas dry
Poles (Cold and Dry)
- Earth’s curvature causes the sun’s rays to strike at a steeper angle. Additionally, because the radiation must travel through a greater depth of the atmosphere, more energy is scattered and absorbed by gases and particles, further reducing the amount of solar energy that reaches the surface. This results in colder temperatures and less evaporation, contributing to the dry, cold climate near the poles
Cryospheric processes:
- inputs (accumulation) —> snow added to a glacier
- outputs (ablation) —> glacier melts
- positive balance —> accumulation > ablation (colder temps)
- negative balance —> accumulation < ablation (warmer temps)
Past events and their impact on cryospheric processes:
- During glacial periods, a significant amount of water moves from the hydrosphere to the cryosphere. For example, during the last glacial maximum, global sea levels dropped by about 120 meters due to the expansion of ice
- In warmer interglacial periods, ice sheets melt —> releasing water back into oceans and seas —> water moves from the cryosphere to the hydrosphere
Future events and their impact on cryospheric processes:
- Recent global warming has reduced accumulation and increased ablation levels. Water moves from the cryosphere to the hydrosphere. This leads to higher global sea levels —> meltwater flows into the oceans and shrinking ice increases the amount of water stored in the hydrosphere
drainage basins
- drainage basin (catchment area for water) —> the area surrounding the river where the rain falling on the land flows into that river (once rain caught within the area, it ends up in the river)
- water shed —> edge of drainage basin —> area of high land that separates the drainage basins —> water on 1 side of high land will end up in one drainage basin and water on the other side of the high land will end up in the other drainage basin
- confluence —> the point at which 2 rivers meet
- tributary —> a small river or stream that joins a larger river
- source —> the start of a river
- mouth —> where the river meets the sea
inputs:
- precipitation
outputs:
- evapotranspiration
- discharge
stores: (CIGSS)
- channel storage - water held in a river
- interception - water stored by trees
- groundwater - water stored in the ground
- soil storage - water stored in the soil
- surface storage - water in puddles, ponds and lakes
flows:
- stemflow - water running down a plant stem or tree trunk
- surface runoff/overland flow
- infiltration - water moving from the ground into the soil
- throughflow - flow of water through soil (downhill)
- percolation - water moves from soil into rocks
- groundwater flow - flow of water through rocks
- channel flow- movement of water within the river channel
water balance
hydrographs
- hydrographs —> shows river discharge over a period of time
- flood hydrographs—> shows river discharge around the time of a storm event
- river regime —> shows the variations in river discharge over a year
- discharge —> volume of water that flows into a river per second (volume of water - m^3) (discharge is measured in m^3/s —> cumecs)
- lag time —> the delay between peak rainfall and peak discharge —> this delay happens because it takes time for rainwater to flow into a river
- peak discharge —> when the river discharge is at its greatest
- rising limb —> where the river discharge increases as rainwater flows into the river
- falling limb —> where the river discharge decreases because less water is flowing into the river
- base flow —> normal flow of river if there weren’t any heavy rainfall events
- storm flow —> extra water added into river because of rain storm
flashy:
• short lag time
• steel rising and falling limb
• higher flood risk
• higher peak discharge
subdued:
• long lag time
• gentle rising and falling limb
• lower flood risk
• lower peak discharge
factors affecting river discharge (flashy and subdued):
- ground steepness: steep —> less time to infiltrate —> surface run-off increases —> river discharge increases// water flows more quickly downhill —> short lag time
- vegetation: more vegetation —> interception increases —> surface run off decreases —> river discharge decreases// vegetation binds the soil together and increases its capacity to store water —> infiltration increases —> surface run off decreases —> river discharge decreases// interception increases —> trees slow the movement of water into river channels —> longer lag time
- soil type: impermeable soils —> infiltration decreases —> surface run off increases —> river discharge increases// infiltration decreases —> results in rapid overland flow —> shorter lag time —> water reaches channel more quickly
- drainage basins —> larger drainage basins: collect more precipitation —> river discharge increases// water has to travel a long distance before it reaches the river channel —> longer lag time// drainage density (amount of rivers and streams over an area) —> lots of rivers and streams in a small space —> rain doesn’t have to travel very far before it reaches the river channel —> short lag time
- urban and rural areas —> urban: covered in impermeable surfaces —> infiltration decreases —> surface run off increases —> river discharge increases// infiltration decreases —> results in rapid overland flow —> shorter lag time —> water reaches channel more quickly
physical factors affecting the water cycle
extreme weather
storms:
- intense storms with heavy rainfall —> soil becomes saturated —> infiltration decreases —> surface run-off increases —> river discharge increases// wind can damage vegetation —> interception and evapotranspiration decreases —> surface run off increases
droughts:
- vegetation dies —> less evapotranspiration —> less precipitation —> drought (positive feedback loop) —> decrease in river discharge
seasonal changes
summer:
- higher temperature cause the ground to be harder and more impermeable —> infiltration decreases —> surface runoff increases
- in summer, runoff levels can be low due to a reduction in rainfall —> soil saturation levels will be low —> therefore rainfall can infiltrate into the ground —> discharge decreases
- more vegetation —> interception and evapotranspiration increases —> surface run off decreases
winter:
- vegetation dies and leaves are lost —> interception and evapotranspiration decreases —> surface run off increases
- in winter, runoff levels can be high due to increased rainfall —> soil saturation levels will be high —> therefore less rainfall can infiltrate into the ground —> discharge increases
human factors affecting the water cycle
deforestation:
short term:
- deforestation —> less evapotranspiration and interception —> surface run off increases —> river discharge increases —> risk of flooding increases (local)
long term:
- deforestation —> less evapotranspiration —> less water vapour in the atmosphere —> fewer clouds form —> less precipitation —> changes in global precipitation patterns —> risk of drought increases (global)
positive feedback loop:
- deforestation to create space for crops —> less evapotranspiration —> less rainfall —> ground becomes drier and less fertile —> new areas of land need to be cleared to grow crops
land use (urbanisation)
- construction creates impermeable surfaces —> infiltration decreases —> surface runoff increases —> river discharge increases
agriculture
- ploughing breaks up the surface of the soil —> infiltration increases —> surface run off decreases
- crops —> interception and evapotranspiration increases —> surface run off decreases (short term)// evapotranspiration increases —> more water vapour in the atmosphere —> clouds form and precipitation increases —> soil becomes saturated —> infiltration decreases and surface run off increases (long term)
- compaction —> livestock and machinery compact the soil —> infiltration decreases —> surface run off increases
- water abstraction —> growth of global population and in particular in countries where climates are drier has resulted in increased water demand —> where precipitation levels are low, an alternative supply is ground water —> soil becomes dry —> infiltration decreases —> surface run off increases —> river discharge increases
river eden case study
facts and location
- the river eden is 145km long and is located in north west of england in cumbria
- the eden drainage basin is in north west england, between the mountains of the lake district and the pennies —> topography —> clouds form —> rain etc
- it’s source is in the pennine hills in south cumbria
- it’s mouth is in the solway firth at the scottish border
physical causes of flooding in the river eden
geology
- upland areas of river eden are mainly covered in igneous rock —> impermeable surface —> infiltration decreases —> surface run off increases// low land areas of the river eden are mainly covered in sandstone and limestone —> permeable rocks —> become saturated so no more water can infiltrate —> surface run off increases —> flashier hydrograph
gradient
- steep gradient —> elevation drops from 690m to 180m —> water doesn’t have time to infiltrate and will run off —> flashier hydrograph
weather
- rainfall is higher than the national average in the eden basin due to topography —> creates orographic precipitation —> around 2800mm annual rainfall in the upland areas —> lead to surfaces exceeding field capacity —> no more water can infiltrate —> runoff increases —> flashier hydrograph
drainage basin shape
- carlisle sits at the confluence of the rivers eden, petteril and caldew—> lots of water coming together at 1 point
- drainage basin is long and thin —> less places for water to go to —> water concentrated towards carlisle —> flashier hydrograph
human causes of flooding in the river eden
deforestation
- deforestation to make space for housing —> 10,000 new homes were built in carlisle —> deforestation —> interception and evapotranspiration decreases—> surface run off increases —> flashier flood hydrograph (short term and long term)
construction
- surfaces tend to be impermeable —> infiltration decreases —> surface run off increases —> flashier hydrograph
farming
- soils become compacted by heavy machinery or trampling by livestock e.g. between 2000 and 2009, there was a 30% increase in the number of cattle in the eden valley —> compaction increases —> infiltration decreases —> surface run off increases —> flashier hydrograph
