water cycle Flashcards
systems
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 —> when energy or matter move from one store to another
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
- positive feedback - when a chain of events amplifies (increases) the impacts of the original event
- negative feedback - when a chain of events nullifies (reduces or stops) the impacts of the original event
positive feedback examples:
- temperatures increase —> ice melts —> less ice cover —> reduced albedo (less of the suns energy is reflected and more is absorbed) —> temperatures increase further
- temperatures increase —> ocean temperature increases —> warm water is less able to dissolve gases —> CO2 is released into the atmosphere —> CO2 is a greenhouse gas —> temperatures increase further
negative feedback examples:
- CO2 in atmosphere increases —> extra CO2 causes plants to grow —> plants remove CO2 from the atmosphere —> amount of CO2 in the atmosphere decreases
water stores/states
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
- water must be physically and economically accessible for humans to be able to use it e.g. groundwater is hard to access so it may not be cost effective to extract it
- as a result, only a small amount of water on the planet can be used by humans
- gas to liquid/ liquid to gas —> condensation/ evaporation
- solid to liquid/ liquid to solid —> melting/ freezing
- solid to gas —> sublimation
- gas to solid —> deposition
- for water to boil or melt, it has to gain energy
- for water to condense and freeze, it has to lose energy
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)
Magnitude of the stores varies overtime:
Evaporation:
- Evaporation occurs when liquid water changes state into a gas, becoming water vapour - it gains energy, normally from solar radiation. Evaporation increases the amount of water stored in the atmosphere
- Long-term changes in the climate can also affect the magnitude of evaporation
- The magnitude of the evaporation flow the supply of water and temperatures e.g. low temperatures and a small supply of water will lead to low evaporation levels// high temperatures and a large supply of water will lead to high evaporation levels
Condensation:
- Condensation occurs when water vapour changes state to become a liquid — it loses energy to the surroundings
- The magnitude of the condensation flow depends on the amount of water vapour in the atmosphere and the temperature e.g. if there is lots of water vapour in the air and there’s a large or rapid drop in temperature, condensation will be high
Cloud formation and precipitation:
- Clouds form when warm air cools down, causing the water vapour in it to condense into water droplets, which gather as clouds. When the droplets get big enough, they fall as precipitation
There are several things that can cause warm air to cool, leading to precipitation:
- Other air masses - Warm air is less dense than cool air. When they meet, the warm air is forced to rise. It cools down as it rises and condenses to form clouds. This results in frontal precipitation
- Topography - When warm air meets mountains, it is forced to rise. It cools down as it rises and condenses to form clouds. This results in orographic precipitation e.g. the pennines
- Convection - As the sun heats up the ground, the moist air rises. As it rises, it cools and condenses to form clouds. This results in convective precipitation
- Water droplets caused by condensation are too small to form clouds on their own. For clouds to form, there have to be tiny particles of other substances (e.g. dust or soot) to act as cloud condensation nuclei. They give water a surface to condense on. This encourages clouds to form
Cryospheric processes:
- Cryospheric processes such as accumulation and ablation change the amount of water stored as ice in the cryosphere
- During periods of global cold, inputs into the cryosphere are greater than outputs - water is transferred to it as snow, and less water is transferred away due to melting
- During periods of warmer global temperatures, the magnitude of the cryosphere store reduces as losses due to melting are larger than the inputs of snow
- The Earth is emerging from a glacial period that reached its maximum 21 000 years ago. There are still extensive stores of ice on land in Antarctica and Greenland, as well as numerous alpine glaciers. There is also a large volume of sea ice in the Arctic and Antarctic
- Inputs (accumulation) —> snow added to a glacier
- Outputs (ablation) —> glacier melts
- Positive balance —> accumulation > ablation (colder temperatures)
- Negative balance —> accumulation < ablation (warmer temperatures)
Past events and their impact on cryospheric processes:
- During glacial periods, a significant amount of water moved 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. This releases 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
drainage basins
- drainage basin (catchment area for water) —> around of land around the river
- water shed —> edge of drainage basin —> area of high land that separates the drainage basins —> water on right side of high land will end up in the right drainage basin and water on the left side of the high land will end up in the left 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:
- transpiration
- evaporation
- 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
- Water balance is worked out from inputs (precipitation) and outputs (channel discharge and evapotranspiration)
- The water balance affects how much water is stored in the basin
- In wet seasons, precipitation exceeds evapotranspiration. This creates a water surplus. The ground stores fill with water so there’s more surface runoff and higher discharge, so river levels rise
- In drier seasons, precipitation is lower than evapotranspiration. Ground stores are depleted as some water is used (e.g. by plants and humans) and some flows into the river channel
- At the end of a dry season, there’s a deficit of water in the ground. The ground stores are recharged in the next wet season (e.g. autumn)
hydrographs
- hydrographs —> shows river discharge over a period of time
- flood hydrographs (storm 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
flashy:
• short lag time
• steep 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
- 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
- drainage basins —> circular basins: water reaches the river at the same time (short travel distance) —> short lag time, high peak discharge —> flashy hydrograph// elongated basins —> water takes longer to reach the river (varied travel distances) —> longer lag time, lower peak discharge —> subdued hydrograph
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 —> even less evapotranspiration —> decrease in river discharge (positive feedback loop)
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 —> surface runoff decreases —> 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 —> 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
long term:
- deforestation —> less evapotranspiration —> less water vapour in the atmosphere —> fewer clouds form —> less precipitation —> changes in precipitation patterns —> risk of drought increases
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 —> 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
- its source is in the pennine hills in south cumbria
- its 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 —> mountainous terrain encourages orographic rainfall —> 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
- eden basin is long and relatively narrow —> increases lag time
- slopes within the basin are steep —> shorter lag time and increase in peak discharge
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
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
5 subsystems of the earth
global water stores:
- hydrosphere —> all the water on earth —> it may be in liquid, solid and gas form
- cryosphere —> 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
eden basin case study
flooding etc
