Water Cycle 2 Flashcards
Explain the importance of the inter-tropical convergence zone
zone of convergence at the thermal equator where trade winds meet
- low pressure belt and migrates with the changing position of the thermal equator.
How does the ITCZ cause heavy rainfall
-steep angle of sun over tropical oceans -> intense solar radiation -> high evaporation
-trade winds transfer water vapour -> ITCZ -> strong convectional currents lift air -> cools, condenses -> clouds -> heavy rain
What is the ITCZ
narrow zone iof low pressure near equator
-where northern & southern air masses converge
How does the thermohaline circulation work
-ocean water in polar region is colder, more salty & denser in tropics so it sinks
-cold sinking water draws in warmer water from ocean surface above, which in turn draws water across surface from Tropics
-movement of water from Tropics draws cold water up from oicean bottom to be warmed again
How does the thermohaline circulation work
-ocean water in polar region is colder, more salty & denser in tropics so it sinks
-cold sinking water draws in warmer water from ocean surface above, which in turn draws water across surface from Tropics
-movement of water from Tropics draws cold water up from ocean bottom to be warmed again
Why are polar regions importanat
2/3 of Earth’s freshwater locked up in cryosphere -> as temp remains below freezing (ice sheets)
global climate warms -> frozen cryosphere water melts -> adding to hydrological cycle
Why are drainage basins referred to as catchment areas
as they catch all precipitation falling within watershed
How do drainage basins lose water
-evaporation, evapotrabspiration
-surface runoff to sea
-percolation into groundwater stores
What prevents the oceans from drying out
-global water budget
-oceans lose water through evaporation -> regain water from precipitation
-surface runoff makes up the difference known as the balance -> if balance was disturbed -> oceans would receive more water
Why does the warming of the global climate lead to an increase in water in the global hydrological cycle
2/3 water locked up in cryosphere
-as global climate ^ frozen cryosphere water melts -> sea -> adding to closed hydrological cycle
Name the 3 pathways water takes when precipitation occurs
-name 2 reasons why these pathways may be delayed
-reach land surface then infiltrate
-run off surface as overland flow (surface runoff)
-be evaporated- taken back into atmosphere
delayed:
-water intercepted -> plants/ buildings before evaporating/ inflitrating into surface
-some water infiltrates & percolates through rocks underneath groundwater -> may be stored as aquifers
explain the physical factors that affect the flow of interception in the drainage basin
- rate of interception dependant on two physical factors: precipitation and vegetation
- interception greatest when rain is lightest and of short duration as the dry leaves and stems have the greatest water storage capacity, if intensity increases then interception is less effective as more will drop off
- denser types of vegetation such as coniferous forests intercept more water than sparser deciduous trees, especially in winter when deciduous lose their leaves
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explain the physical factors affecting infiltration
1) precipitation intensity - infiltration-exces
explain the physical factors affecting infiltration
1) precipitation intensity - infiltration-excess overland flow will occur when rainfall intensity exceeds infiltration capacity, meaning that the water flows over the surface and infiltration is reduced
2) vegetation cover- roots help to break up the soil, increasing the infiltration rate
3) soil and rock type- infiltration rates will increase as porosity and permeability increase
4) water table depth- as the water table rises during prolonged rainfall the soil will become saturated, reducing infiltration
5) slope gradient- as gradient increases, more water will flow over the surface, reducing infiltration
explain the physical factors that affect the rate of percolation and groundwater flow
the permeability of the rock and the angle of the rock strata as a steeper gradient will allow gravity to operate more effectively
- the rate of P and GWF increases with porosity, impermeable rocks like granite prevent any percolation
- areas with permeable rock will absorb the water and create groundwater storage and an aquifer (a permeable rock which shotes water)
- porosity relates to the total volume of pore spaces and is greatest in coarse-grained rocks such as sandstone, while pervious rocks such as limestone have joints and bedding planes along which water can flow
how do you calculate a water budget?
precipitation = discharge + evapotranspiration + - change in storage
P = Q + E + - S
what are water budgets?
show the annual balance between inputs (precipitation) and outputs (evapotranspiration) in any given area
what are the different parts of a water budget?
monthly temperature
potential evapotranspiration
precipitation
water surplus
soil moisture utilisation
soil moisture deficiency
soil moisture recharge
what is soil moisture surplus?
precipitation exceeds than potential evapotranspiration
- soil water store is full -> soil moisture surplus for plant use, runoff and ground water recharge.
what is soil moisture utilisation?
potential evapotranspiration exceeds precipitation
-more water evaporating from ground surface & transpired by plants than is falling as rain
-soil moisture -> used up by plants/ lost by evaporation
what is soil moisture deficiency?
deficiency of soil water -> store is used up
potential evapotranspiration exceeds precipitation.
plants must adapt to survive- irrigation is needed
what is soil moisture recharge?
precipitation higher than potential evapotranspiration, soil water starts to fill again
what is field capacity?
when soil is full of water & cannot hold any more.
what is potential evapotranspiration?
amount of water lose through evaporatiojn & transpiration in any given period
what is infiltration capacity?
max rate at which the water can be infiltrated
What is effective rainfall
amount of precipitation remaining after evaporation
What is a river regime
annual pattern of flow
Name the 2 types of river regime
-simple regimes -> where river experiences period of seasonally high discharge followed by low discharge
-complex regimes -> where larger rivers cross several different relief and climatic zones, therefore experience the effects of different seasonal climatic events
Provide an example of complex river regimes
-amazon, brazil
-high flow: wetter season
-low/ no flow: drier season
-seasonable variability: moderate variability- fed by Andean rivers
-human influences: increasing
What are the major influences in the river regimes in the amazon, Brazil
-rainforest climate
-seasonal precipitation- rainfall in every month but divided into higher and lower rainfall seasons
-evapotranspiration levels very high
What is a hydrograph
a graph showing the discharge of a river at a given point over a period of time
What is a storm hydrograph
shows how river responds to a particular storm & displays both rainfall and discharge
What is the rising limb on a storm hydrograph
line on a storm hydrograph which shows the discharge rise up to its peak discharge
What is the lag time on a storm hydrograph
gap between peak (maximum) rainfall and peak discharge (highest river level)
Name the 6 influencing factors in the hydrological cycle
-amount of precipitation; directly imacts drainage discharge
-type of preicpitation (rain, snow; can act as temp store & large fluxes can be released into system
-seasonality; seasonal patterns of rain will impact physical processes operating drainage basin
-intenisty of precipitation; impacts flow
-variability
-distribution of precipitation within a basin;
Name the 2 flows in the drainage basin
-interception; process where water is stored in vegetation
-infiltration; process where water soaks into soil
What are the 3 components of interception
-interception loss; water that is retained by plant surfaces & later evaporated
-thrpughfall;when rainfall is intense & water drops from leaves
-stem flow; when water trickles along branches, twigs
What is the infiltration capacity
maximum rate at which rain can be absorbed by soil
The rate of infiltration depends on what 6 factors
-amount of water in soil
-soil texture
Name the 2 drainage basin system outputs
-evaporation; when moistures lost into atmopshere from water surfaces
-transpiration; when waters lost from plants through pores & transferred to atmosphere
Name the 5 physical factors that influence the drain basin cycle
-climate; influences type & amount of precipitation, evaporation
-soils; dtermine amount of infiltration & throughflow
-geology; impacts percolation, groundwtaer flows
-relief; impact precipitation totals
-vegetation; impacts interception, infiltration, overland flows, transpiration rates
Name the 5 human factors that influnece the drainage basin system
- overabstraction
- river management (creation of dams and reservoirs)
- deforestation
- cloud seeding; impacts precipitation -> silver iodide pellets attract water droplets -> ^ rainfall
- urbanisation
- changing of agricultural land use
Describe deforwstation issues in Amazonia
-over 20% of forest has been destroyed
-amazon forests contain 60% of worlds rainforests
-trees remove CO2
-destroying these trees -> greenhouse gas emissions
What is peak discharge
time when river reaches its highest flow
What is the falling limb
part fo storm hydrograph where discharge starts to decrease
What is base flow
normal day-to-day discharge of river
explain a flashy river on a hydrograph
- short lag time
- peak discharge high
- rising limb steep
- more likely to cause flooding
- rainfall reaches river quickly
explain a flat river on a hydrograph
- long lag time
- peak discharge low
- gentle rising limb
- rainfall reaches river slowly
- less likely to cause flooding
Explain 5 ways urbanisation impacts the hydrological processes
-building activity -> clearing of water of vegetation which exposes soil, overland flow
-high density of buildings -> rain falls on roofs -> drains
-drains and sewers -> reduce distance storm water travels before entering channel
-bridges -> restrain free discharge of floodwaters
what are the four types of drought in order of when they occur
meteorological drought
hydrological drought
agricultural drought
socio-economic/famine drought
What is meteorological drought
occurs when long-term precipitation is lower than normal
-strong winds, high temp
-> loss of soil moisture
what is agricultural drought
decrease in precipitation -> decline in soil moisture, soil water avaliability -> reduced plant growth, biomass
-> crop yields decline, livestock declines
->rural industries affected
what is hydrological drought
reduced precipitation & high rates of evapotranspiration -> reduced stream flows, falling groundwater levels
what is socio-economic/famine drought
widespread failure of crops and natural vegetation, demand is greater than supply
-loss of antural vegtation
->food shortages on seasonal scale
Name the 3 measurements of drought
Explain the El Nino-Southern Oscillation (ENSO)
refers to the coupled ocean-atmospheric cycle where a large mass of warm water in the equatorial Pacific alters its position during the cycle. (normally happens at Christmas)
what are the normal conditions conditions in the Pacific basin compared to those during an el Nino?
normal conditions:
- trade winds blow from east to west along the equator
- air pushes warm moist air westwards to Indonesia & cold dry air to South America
- the warmer air in the west -> low pressure & in east air cools &sinks -> high pressure
- warm, moist air rises, cools & condenses forming rain clouds
- thermocline, upwelling
el nino:
- the air circulation loop is reversed, air moves west to east and so Peru gets wetter due to warm air and Indonesia gets dryer due to colder air leading to forest fires and droughts.
- the trade winds get weaker and warm surface water drifts across the Pacific towards S America leading to a drought in the west
- less upwelling of cold on east, cancels out normal temp difference
- it impacts the tropics the most
la nina:
-trade winds strengthen
-trade winds push warm water west -> sea level up in Indonseia, Phillipines
-low pressure develops with strong convectional uplift as warm water heats atmosphere
-^ in equatorial undercurrent
sahel region case study
the norther Sahel is seeing a 30-40% annual departure from normal rainfall
- according to the CSIRO, the drought of the late 20th century were caused by air pollution (sulphur-based aerosols) generated in europe and north america. this led to atmospheric cooling changing the global heat budget and atmospheric circulation so that tropical rains associated with the ITCZ did not arrive therefore causing drought
- over abstraction here as illegal wells were dug as costs were too high for the majority of the population
- in 2005 a study by NOAA said that the drought may have been caused by higher sea surface temperatures caused by anthropogenic climate warming. the rain bearing winds appear to fail when the sea temps are higher than average
POP PRESSURE
- population growth rates form 2.5-4% has led to increased demand for food and water, natural drylands ecosystems converted into farmland, over cultivated, over cultivation, over grazing and deforestation has led to desertification
- led to less transpiration from vegetation
- poor soil quality and erosion
What is desertification
degradation of land in arid & semi-arid areas
-result from: climatic variations, human activities
BRAZIL DROUGHT
AUSTRALIA DROUGHT
have suffered from: agriculutral, hydrological droughts
-more than half of farmland negatively affected
-reservoir levels have fallen -> water supplies to australian cities threatened
What is a wetland
an area of marsh with water that is static, or flowing
what are 5 impacts of drought on wetlands
- less river and groundwater flow into the wetland -> areas of open water shrinking and drying up.-> habitat loss
- soil moisture reduces & soil dries out -> vulnerable to erosion-> less able to store water in times of flood.
- can lead to overbaked soils leading to increased difficulty for growing crops, increased risk of forest fires
- concentrations of pollutants increase, further reducing populations of different species
- organic soils oxidise and break down releasing carbon into the atmosphere
Name 3 key functions of wetlands
-act as water filters -> trapping & recycling nutrients
-act as temporary water stores ->
Name 3 environments at risk of flooding
-low-lying parts of flood plains & river estuaries
-where low-lyinjg areas are partially urbanised with impermeable surfaces
-small basins -> subject to flash flooding ->
Name 3 meterological causes of flooding
-intense storms -> flash flooding
-prologed heavy rainfall
-rapid snowmelt
Why is Bangladesh a flood-prone country
land of floodplains and deltas
-80% of bangladeshi ppl are exposed to flood risk
-rivers; ganges, padma -> swollen twice a year by meltwater from Himalayas & summer monsoon
explain the cumbria floods of 2015 and storm Desmond
- cumbria is vulnerable to orthographic rainfall due to the upland area
- the combination of warm wet westerly winds plus uplands makes them one of the wettest places in England
- they saw severe flooding in 2005,2009 and 2015
storm Desmond
- december 2015 due to deep Atlantic low-pressure system (depressions)
- fronts stretched across northern Britain bringing prolonged and heavy rainfall through a warm conveyor (jetstream)
- 5200 homes destroyed
- on 5th December, honester pass recorded 341.4mm of rain in just 24 hours
- 61,000 homes lost power when an electrical substation was flooded
what caused the flooding of storm Desmond
1) a conveyor of warm and wet air tracked towards the UK from the carribean
2) the cumbrian feds created orographic (relief) rainfall
3) the moist air mass stayed over cumbria for up to 48 hours, delivering record amounts of rain
4) there was too much rain for the already saturated ground to absorb as November 2015 has been the wettest November since 1910. overland flow carried the excess water to the rivers and steep cumbrian slopes accelerated this.
5) significant flooding cured at river confluences at cocker mouth and Carlisle
6) impermeable surfaces and drains blocked by debris meant that the surface water followed rapidly and directly into the already over-filled river channels
Name 3 flood-producing conditions
-intense precipitation over short period of time
-sudden snow me;t
-unusually heavy, prolonged rainfall
Name the economic impacts of flooding
- structural damage to buildings and infrastructure (e.g. bridges)
-destruction of crops and loss of supplies
- higher insurance premiums/refusal of insurance
- lower property values
- loss of livelihoods (factories, farming)
- drop in tourism
what are the social impacts of flooding
- stress and grief
- spread of water-borne diseases
-death & injury
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what are environmental impacts of flooding
- natural moderate floods can be beneficial to wetland ecosystem by encouraging nutrient disposal, breeding and migration
- recharge of groundwater supplies
– environments already degraded by human activities, flooding becomes more negative - excessive overland flow brings too much sediment and washes too many nutrients into ecosystems leading to eutrophication or pollution from chemicals which degrade ecosystems
recharged groundwater stores
increased connectivity between aquatic habitats
soil replenishment
for many species, flood events trigger breeding, migration and dispersal
Give an example of flooding experineced by the UK in summer of 2007, 2015 & 2016
-flooding caused from prolonged heavy rainfall
There were recriminations after the apparent inadequacy of flood protection measures. The following were singled out for blame:
budget cuts in the amount of money being spent on flood defences
an EU Directive that puts environmental conservation ahead of the regular dredging of rivers
poor land management, resulting in blocked ditches
global warming
How does climate change impact hydrological cycle
precipitation
A warmer atmosphere has a greater water-holding capacity
It is argued that the mode of precipitation may be more important than the amount in determining the impacts
Widespread increases in rainfall intensity are expected more than large increases in total amounts
Areas of precipitation increase include the tropics and high latitudes
Areas of precipitation decrease lie between 10° and 30° north and south of the Equator
The length and frequency of heatwaves is increasing in some locations and is resulting in the increased occurrence of drought
With climate warming, more precipitation in northern regions is falling as rain rather than snow
Evaporation and Evapotranspiration
Evaporation over large areas of Asia and North America appears to be increasing
Transpiration is linked to vegetation changes, which in turn are linked to changes in soil moisture and precipitation
what stores and flows will be impacted by climate change
runoff (flow) leading to flooding
soil moisture stores leading to drought
snow -> warmer temps mean more snow is falling as rain
ice
permafrost
reservoir, lake and wetland storage
Summary of short-term climaste change impacts on water supply
-depleted aquifers -> problems with groundwater
-
What is ecosystem stress
constraints on the development/ survival of ecosystems
-constraints can be physical, chemical, biological
What is ecosystem resilience
capacity of an ecosystem to recover from disturbance/ withstand ongoing pressure
Name 4 physical factors in which contribute to flooding
soil depth -> deeper soil absorbs more water -> less runoff
slope -> steeper-angled slope -> less water absorbed -> more runs off
rock type -> permeable rock -> greater infiltration -> less runoff
vegetation -> more vegetation -> higher levels of interception -> reduces rainfall, increases lag time
Name 3 ways people can exacerbate flood risk
-changing land use -> deforestatio, urban development -> ^ runoff
-mismanagement of rivers -> e.g. straightening river channels can improve flow of water at 1 location but ^ flood risk downstream
-poor maintenance of rivers
