Water Cycle 💧 Flashcards
what is the systems approach?
group of interacting parts connected by flows of energy or matter
open - energy and matter can enter and leave
closed - only energy can enter and leave, matter cant
cascading systems - where output of one subsystem is an input to another
dynamic equilibrium in water cycle
tendency towards a natural state of balance between inputs and outputs
- change triggers + or - feedback
closed system - no water enters or leaves, recycled
drainage basin = open system, inputs and outputs can change
equilibrium upset by natural (storm events) and human changes
Positive feedback in the water cycle
- temperature rise
- evaporation increases
- amount of water vapour in atmosphere increases
- greenhouse effect increases
Negative feedback in water cycle
- temperatures rise
- evaporation increases
- increase water vapour, causes more clouds to form
- increased cloud coverage, reflect more sunlight back to space
- temperatures fall
how are systems affected by feedbacks?
if input and outputs are balanced = dynamic equilibrium
- positive - moves system further from equilibrium
- negative - moves system closer to equilibrium
What is an open system?
Both energy and matter can enter and leave
- drainage basin, water (energy from sun and water)
- rainforest, carbon
What is a closed system?
Matter can’t enter or leave but energy can
- carbon cycle (energy from sun enters and leaves, but carbon remains same)
Flows in the water cycle
Evaporation - liquid to gas, uses solar energy, can be affected by seasons or glacial periods
Condensation - gas to liquid, water vapour cools to dew point, loses energy
Cloud formation - warm air cools and condenses onto condensation nuclei, varies seasonally and location
Precipitation - main flow from atmosphere to ground
Cryospheric processes - accumulation and ablation
Natural changes that impact the water cycle
Seasonal changes
Storm events
Human changes that impact water cycle
Deforestation
Urbanisation
Farming
water abstraction
climate change
what are ‘processes driving change’?
factors affecting the size of stores in the water cycle
dictated by:
- flows (eg evaporation)
- global factors
- local factors
local processes driving change
flows and transfers
(in a drainage basin)
affecting by physical and natural factors
global processes driving change
cryospheric processes
clouds and precipitation
evaporation
condensation
climate change
effects of evaporation on the water cycle
increases the amount of water stored in atmosphere
from hydrosphere, biosphere etc
magnitude (rate) varies due to location and season:
- amount of solar energy
- availability of water (pond vs field)
- humidity (higher = less)
- temperature (warmer air holds more water)
effects of condensation on the water cycle
happens when air containing water vapour cools to dew point
(cool air holds less water)
decreases amount of water stored in atmosphere
condense on surfaces or particles below dew point temperature
magnitude depends on
- amount of water vapour in atmosphere
- temperature (large drop = more condensation)
- condensation nuclei
effects of cloud formation and precipitation on the water cycle
precipitation returns atmospheric water to terrestrial
- causes, water vapour cooled (see next)
magnitude depends on
- seasons (eg UK, more rain in winter than summer)
- location (higher at tropics than poles)
distribution affected by global atmospheric circulation model
- hot at equator = evaporation, low pressure
low pressure = clouds
causes of rainfall (3)
frontal - warm air is less dense, so when meets cool air, forced above
cools as it rises and condenses
orographic - warm air meets mountains, forced to rise
causes it to cool and condense
convectional - sun heats up ground, moisture evaporates and rises
cools as it gets higher, condenses
effects of cryospheric processes on the water cycle
changes to the amount of water stored in cryosphere
Major store of water
magnitude depends on
- season (more ice in winter)
- temperature
glacial periods - inputs in cryosphere greater than outputs, no melting
interglacial - outputs larger than inputs, melting
- causing sea level rise, more volume in hydrosphere
varies on different scales, annual or thousands of years (glacial periods)
effects of climate change on water cycle (global factors)
last ice age = increased size of store in cyrosphere
less storage in the hydrosphere
outline drainage basins
- area of land drained by a river and its tributaries
- boundary is called the watershed
- open systems with inputs and outputs
inputs in a drainage basin
precipitation
- rain, snow etc
stores in a drainage basin
interception storage
(especially in woodland)
temporary, evaporates or throughfall
vegetation storage - water taken up by plants
surface storage - puddles, ponds and lakes
soil storage - moisture in soil
groundwater storage - water stored in ground, soil or rocks (aquifers)
channel storage - water in river channel
what is the water table?
top surface of the zone of saturation (area of soil or rock where all pores are full of water)
level where water has saturated the ground
flows in a drainage basin
infiltration - water soaking into soil
influenced by: saturation, soil type
surface runoff - happens as water falls faster than infiltrated
throughfall - water dripping through leaves
stemflow - in stem or tree trunk
percolation - water moving downwards through bedrock and soil below water table
throughflow - lateral flow through soils above the water table
interflow - through rocks above water table
groundwater flow - water flowing below water table through permeable rock, very slow
base flow - groundwater flow that feeds into rivers
channel flow - water flowing in river
outputs in a drainage basin
evaporation - water vapour in atmosphere
transpiration - evaporates from leaves into atmosphere
evapotranspiration
river discharge - into ocean
what is the water balance?
balance between inputs (precipitation) and outputs (discharge and evapotranspiration)
water surplus - inputs exceed outputs
saturation, more runoff, river levels ruse
water deficit - outputs higher than inputs
groundwater stores depleted, used but not replaced
recharged in wet seasons
outline a hydrograph (flood/storm)
shows river discharge over a period of time, a storm event
peak discharge - river discharge at its highest
lag time - delay between peak rainfall and peak discharge
takes time for water to flow into river
short lag time increased peak discharge
rising limb - river discharge is increasing
falling limb - river discharge is deceasing, less water flowing into river
throughflow - water passing throigh gaps in soil into river
groundwater (base) flow - main supply in normal conditions, from groundwater
Purpose of hydrograph
Predict flooding
after storm or annually
Natural factors effecting hydrograph
size of basin
- larger basins catch more water, high peak
- smaller basins have less distance, shorter lag time
shape of basin
- circular basins are flashier, all point in watershed similar distance, water reaches river at same time
- long narrow basins, less flashy
steepness - topography
- flows quicker downhill, short lag time
less time to infiltrate, runoff higher
rock and soil type
- impermeable rocks reduce infiltration, more runoff, increase peak discharge, decreased lag time
Human factors effecting hydrograph
Farming
- ploughing increases infiltration = less discharge, increased lag time
- livestock compact soil - more runoff, decreased lag time
Deforestation
- less interception = higher discharge
- more runoff - shorter lag time, more discharge
Urbanisation
- impermeable surfaces - increase runoff, higher discharge and decreased lag time
Water abstraction
- water stores in aquifers depleated, less water in channel so lower peak discharge
what is a river regime?
annual hydrograph
show river discharge over a year
- show patterns and seasonal variations
show peaks and lows
influenced by temperature, vegetation etc
physical factors that affect water cycle
- storms and precipitation
- seasonal changes
- vegetation
human activities that affect water cycle
- farming practises
- deforestation
- urbanisation/ land use change
- water abstraction
- climate change
how do storm events affect the water cycle
intense storms mean more precipitation - greater peak discharges
more surface runoff, infiltration to slow/ soil saturated
arger input of water into system
drought also has impacts
- reduced water storage in rivers and lakes
- less vegetation so less interception
- groundwater stores important
how do seasonal changes affect the water cycle
affects size of inputs flows and stores
in winter
- reduce size of flows
- increased storage in cryosphere
- larger flows and stores as ice melts
most plants vary by season
- more plants in summer, more interception
- increased lag time (less runoff)
- decreased peak (more outputs)
- more evapotranspiration
summer - dry soils, less rainfall = runoff
winter - more rain, saturation = runoff
how do farming practises affect the water cycle
affect infiltration
increase infiltration/ reduce runoff:
- ploughing, break up soil
- crops, increase infiltration and interception
decrease infiltration/ increase runoff:
- livestock, compact soils
- irrigation, not all water can infiltrate fast enough
ground water/ river levels fall if water abstracted from them
how does deforestation affect the water cycle
reduces interception
- increase runoff
- exposed to soil erosion
less evapotranspiration
- less moisture returned to atmosphere
= decine in regional rainfall
how does urbanisation affect the water cycle?
impermeable surfaces
- reduced infiltration and increased runoff
deforestation
- less evapotranspiration
how does water abstraction affect the water cycle
more water taken from stores, reduces volume = depleated
(to meet demands for people)
eg lakes, rivers, and groundwater
rate of recharge slower than rate of use
dry seasons increase abstraction
- needed for consumption and irrigation, depleted more
how does climate change affect the water cycle?
reduces storage in cyrosphere
- melts and enters hydrosphere
= sea level rise
wetter areas wetter and drier drier
- impacts farming and yeilds
more freuqent/ intense storms
- more precipitation inputs
increased temperatures = more evaporation
- more water vapor in atmosphere
Outline dynamic equilibrium in the water cycle
Tendency for a natural state of balance within the water cycle
Global cycle is a closed system, no input or outputs, just recycled
Drainage basin has inputs (precipitation) and outputs (discharge and evaporation)
Storm events and human activity can disrupt equilibrium
Relationship between water and carbon in atmosphere
Carbon dissolved in water = acid rain, leads to ocean acidification
Water vapour and carbon dioxide released in volcanic eruptions
Increased carbon in atmosphere leads to global warming which increases evaporation
And therefore precipitation
Why is the water cycle important for life
- Provides habitats in solid forms eg Antarctic animals
- And liquid forms eg oceans
- Liquid water to drink, can be used as fuel
- water vapour in atmosphere used in photosynthesis, needed for plant growth on land and in sea and releases oxygen
Percentage of water in spheres
69% freshwater in cryosphere
0.3% liquid in hydrosphere
0.04% water vapour in atmosphere
what causes change to water balance?
farming
deforestation
mining
physical factors affecting flood risk
heavy/antecedent rainfall
(rainfall before)
soil saturated = more runoff
geology - impermeable rock increases surface runoff
shape/size of drainage basin
human factors affecting flood risk
deforestation
- reduced interception
- more runoff
farming
- compact soil = more runoff
- leads to deforestation
land use change
- urbanisation = impermeable surfaces
- more runoff
what is an aquifer?
water infiltrates ground and collects in spaces in porous rocks
eventually becomes saturated
flows slowly through spaces
stores in global water cycle
water vapour in atmosphere
surface storage
interception storage
ice/snow
oceans
groundwater stores - water stored in porous rocks
how do magnitude of stores vary?
over time
- seasonal
- glacial/ interglacial
over scale
- local (drainage basin)
- global
factors affecting infiltration rates
level of saturation
compacted or frozen = less
relief, steeper = flows before it can infiltrate
vegetation cover = less, interception and evapotranspiration
