Year 13 Physical Geography

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What does the systems theory enable us to understand?
It enables us to conceptualise the main water stores and pathways at a global scale, aswell as understand the role of the local hydrological processes within the wider geological system
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What is a system?
Any set of interrelated components that are connected together to form a working whole, characterised by inputs, stores, processes and outputs
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What is a closed system?
Occurs where there is a transfer of energy not matter between the system and its surrounding (the inputs come from within the system)
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What is an open system?
Recieves inputs from other systems and transfers outputs energy and matter to other systems aswell
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Why is the hydrological system closed?
All the water is continually circulated through the stores and there is a constant amount of water in the sytstem. The system does not change as there are no gains from or losses from other systems
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What is the hydrological cycle driven by?
Solar energy, gravitational potential energy that is converted to kinetic energy as the water moves...
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What is the global water budget?
Annual balance of water fluxes and the size of the water stores (oceans, atmo, bio, cryospheres and ground and surface water
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How is water replenishable?
The water stores have different residence times but are in constant circulation, albeit at various speeds
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Why is fossil water not replenishable?
It is water that has been enclosed in an undisturbed space, usually groundwater in an aquifer for a millenia or longer - in dry areas such as the Sahara fossil water may be extracted for human purposes but there is little to no recharge
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What is a drainage basin?
An area of land that is drained by a river and its tributaries and is separated from neighbouring basins by a high area of land called a watershed, it is an open system as it is linked to other systems
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What is the ITCZ?
Inertropical Covergence Zone
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How does the ITCZ work and how does it influence precipitation?
Intense solar radiation which fuels the convection of warm, humid air, resulting in condensation and precipitation (convectional precipitation)
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Where is the highest rainfall levels in the world?
Mawsynram, India- June -September monsoon season
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Where is the lowest precipitation level found in the world?
Quillagua, Atacama Desert where there are high levels of atmospheric pressure
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What determines the distribution of precipitation?
Continentally (distance from the sea), continental interiors such as the Gobi Desert in Asia or Alice Springs in Australia are far from the moisture of the maritime air masses
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What complicates the distribution of precipitation?
Relief, such as mountains, prevailing winds whicha are forced to rise over the higher altitudes. This is called orographic precipitation
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What is interception?
Raindrops prevented from falling directly onto the ground surface by vegetation- water reaches ground by stem flow or throughfall where the undergrowth may intercept again
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What is the rate of interception affected by?
Precipitation and vegetation. Interception greatest when precipitation is light and of short duration, as dry stems and leaves have the greatest water storage capacity, as vegetation becomes wetter, the storage potential decreases
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How does the vegetation type affect interception?
Denser vegetation intercepts more than vegetation with high levels of spaciality, also affected by seasons
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What is infiltration?
Movement of water vertically downwards through the pores in the soil and the infiltration rate is the maximum rate at which the soil can absorb precipitation
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What factors affect the rate of infiltration?
Pre-saturisation of the soil, gravity (relief?)
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Once in the soil, how does the water move?
Through throughfall, water moves vertically and laterally- it is a downslope movement under the influence of gravity
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What is direct runoff (overland flow)?
Water flowing over the surface of the land
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What are the two types of direct runoff?
Saturated overland flow and infiltation-excess overland flow
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What is saturated overland flow?
When water accumulates in the soil until the water table reaches or ponds on the surface, forcing further rainfall to run off the surface- particularly common where the soils are thin and are of moderate permeability
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How do concavities near a stream or riverbank cause saturated direct run off?
They often have high moisture levels and may produce saturated overland flow in a rainstorm cycle
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When does infiltation-excess overland flow occur?
When the rainfall intensity exceeds the infiltration capacity, so the excess water flows over the ground surface- increases the risk of flooding downstream
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What is percolation?
Water moving downwards into the groundrock - water fills spaces within permeable or porous rock creating groundwater storage called an aquifer . This will happen when the permeable layer lies above an impermeable rock layer so the water can percolate
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no further and creates a saturated zone
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What is the water table?
The upper layer level of groundwater storage- the saturated zone
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How does water move as groundwater?
Water may move laterally as groundwater if the geological structure allows it
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What is the rate of percolation and groundwater flow dependent on?
The porosity of the rock and its permeability, -porosity relates to the total volume of pore spaces, greatest in rocks such as sandstone.
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Do permeable or impermeable rocks create faster conditions for groundwater flow?
Permeable whereas in impermeable rocks e.g. granite it is prevented
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How does the angle of the rock strata increase groundwater flow?
Steeper gradient allows gravity to work more effectively
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What are physical factors affecting drainage basin outputs?
Evaporation and transpiration; evapotranspiration= total amount of moisture removed from a drainage basin by processes of evaporation and transpiration
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What is transpiration?
Biological process by which water is drawn upwards from the soil by plants and evaporated through the stomata
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What factors affect the rate of evapotranspiration?
Temperature, vegetation cover, wind, soil moisture content
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What is channel flow?
Water that has collected to flow in a rivulet, stream or river and is another output of the drainage basin. The discharge of a river is the volume of water passing a specific guaging station per unit of time in cubic metres per second
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What is channel flow dependent on?
Precipitation levels, contributions from drainage basin e.g. surface runoff, throughflow or groundwater flow
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Name a case study for the human disruptions to the drainage basin
Amazonia - changing the speed of processes, creating new stores, extracting water, hard engineering e.g. overflow areas
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What is cloud seeding?
Attempt to change the amount or type of precipitation by dispersing substances into the air that serve as cloud condensation nuclei (hygroscopic nuclei). Produced reliable results that make it a dependable and affordable scheme - still debated
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Exmaple of somewhere where cloud seeding has been used
Bejing, China before the Olympic Games to clear the air of pollution + Alpine Meadows ski area in California + Texas to reduce impact of drought
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How does urbanisation affect the drainage basin?
Impermeable surfaces that reduce infiltration and increase surface run off + throughflow through artificial drains, stream and river discharge increase as a result
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Where has urbanisation increased the impacts of a flood?
Winchester and Maindenhead (2014), Carslile, Manchester and York (2015)
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How does dam construction disrupt the drainage basin?
Increase surface water stores and evaporation and reduce downstream river discharge
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Case study?
Aswan Dam in Egypt, estimated evaporation losses of 10-16 billion cubic metres every year- 20-30% water loss of the Egyptian volume of Nile River water
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How has groundwater abstraction distrupted the drainage basin?
In some locations, groundwater is extracted from aquifers faster than it is replaced causing reduced groundwater flow and a lower water table. In other areas it has reduced industrial activity or deforestation has increased groundwater stores
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which increases the risk or groundwater flooding if the water table reaches the land surface
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What is a water budget?
Shows annual balance between inputs (precipitation) and outputs (evapotranspiration + channel flow)
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What is the equation for water budget?
Precipitation=channel discharge + evapotranspiration +/- change in storage
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What does this equation show?
Direct comparison of natural water supply and demand, making it possible to identify the time periods when precipitation exceeds evapotranspiration (positive water balace) or where there is a negative water balance -evapotranspiration exceeds
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precipitation
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What does a soil moisture budget graph show?
Annual changes in precipitation and potential evapotranspiration which allows assessment of impact on soil moisture availability in different climatic locations- helps understand the vulnrability of terrestrial ecosystems + agricultural challenges
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What is soil moisture surplus?
Precipitation greater than potential evapotranspiration and the soil water store is full,so there is a surplus of soil moisture for plant use, runoff + recharging groundwater supplies - soil field capacity
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What is soil moisture utilisation?
Potential evapotranspiration increases and exceeds precipitation so there is more water evaporating from the ground surface and being transpired from plants that falling rain so the water is gradually used up
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How may high temperatures affect the local water budget?
Cause maximum evapotrapiration, precipitation at a minimum so plants use up the soil moisture faster - river levels will fall and crops will need irrigation
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What is soil moisture deficiency?
Soil water has been used up by high rates of evapotranspiration and minimum precipitation- plants can only survive if they are adpated or are irrigated
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What is soil moisture recharge?
When potential evapotranspiration decreases so it is lower than precipitation, and the soil store starts to fill up again
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What is field capacity?
Soil full of water and cannot hold anymore
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What is a river regime?
Describes the annual variation in the discharge of a river
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Why may the river regime of the Nile river have changed due to the Aswan Dam?
Flow of Nile was reduced by about 65% and became regulated between the seasons so that the flood peaks in September were severely reduced
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What are some factors that may affect a river regime?
Drainage basin area, maximum altitude, altitude variations, geology, mean annual precipitation, mean discharge, main land use, human influence
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What is a storm hydrograph?
Shows variations in a river's discharge at a specific point over a short period of time - the shape of the storm hydrograph changes as a result of physical and human factors and can be described as flashy or subdued
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What is a flashy hydrograph?
Indicates rapid increase in discharge and perhaps a high risk of a sudden flood
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What is a subdued hydrograph?
The changes of water discharge change far more gradually
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What is the rising limb of a hydrograph?
Increase in discharge in response to surfce runoff and throughflow from a rainfall event, until peak flow is reached
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What is bankfull discharge?
When a river's water level reaches the top of the channel- any further increase will result in flooding of surrounding land
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What is the falling limb?
Decline in discharge that occurs after a peak flow- usually less steep than the rising limb because throughfall is being released relatively slowly into the channel
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What is the lag time?
Difference in hours and minutes between the time of maximum precipitation and peak discharge - varies on drainage basin and conditions
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What is the storm runoff?
Part of the river flow derived from the immediate rainfall event - the msot rapid transfer of water occurs overland and via throughfall
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What is the approach segment?
Shows the discharge of the river before the storm
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What are some factors that would affect the river discharge?
Drainage basin size, shape (circular=fastest) + relief (steep slopes=faster), soil type (low porosity=slower e.g. sandy), rock type (impermeable/permeable), drainage density (lots of surface streams will increase discharge), natural vegetation,
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land use (urban), precipitation intensity, precipitation duration, snowfall, evapotranspiration rates
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How does this link synoptically?
Regeneration and planning, sovereignity over water..
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What are defecits within the hydrological cycle?
Droughts, National Drought Mitigation Centre in USA describes drought as an 'insidious hazard of nature'
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What percentage of the global population does the most severe dought conditions affect?
18%
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What is the main hysical cause of drought?
The global atmospheric circulation system
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What is a meterological drought?
Occurs when long term precipitation is lower than normal but there is no set concensus of minimum precipitation that causes a drought - they are region specific as the deficiency of rainfall is caused by the climate
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What is an agricultural drought?
Occurs when there is insufficient soil moisture to meet the needs of a particular cro at a particular time - caused by a number of factors e.g. precipitation shortages, differences between actual and potential evapotranspiration, soil water defecit
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and reduced groundwater supplies/ reservior levels. Can lead to crop failures/ depletion- typically present aftermeterological drought but before a hydrological drought
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What is a hydrological drought?
Occurs when there are deficiencies in surface and subsurface water supplies e.g. rivers, reserviors, lakes and groundwater, originates with a deficiency of precipitation but usually occurs after an agricultural and meterological drought as it takes
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longer for the deficiencies to reach the components of the water cycle such as soil moiture, stream flow and groundwater/reservoir levels
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What is a socio/economic drought?
Occurs when the water demand for social and economic purposes e.g. irrigation or HEP exceeds water availability, could be related to a lack of precipitation or overuse of supplies - differs from other droughts as it depends on the suply and demand
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What are the general processes taking place in the water cycle?
Intense solar radiation at the equator wams the air which rises and starts convection, the air cools and rises and water vapour condenses to form clouds and rain
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What is the sub-tropical high pressure zone created by?
Where air that had risen at the equator has cooled and sinks to form a belt of high air pressure and hot, dry conditions. The air returns to ground level a the equator and creates trade winds
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What happens when trade winds meet?
Trade winds meet at the Intertropical Covergence Zone (ITCZ) where the warm air rises - the position of the ITCZ moves with the seasons
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When is the ITCZ in the northern hemisphere?
In the summer June -August and then it moves to the Southern Hemisphere during its summer
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What does the movement of the ITCZ cause?
Causes alternating wet and dry seasons in the tropics - the warm air moving from the subtropics and the mid-latitudes meets the polar air from the polar front which causes condensation and rainfall
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What causes the movement of air?
Warmer air rises into the polar front jet stream and is transfered at high altitude towards the poles which create movement of air at ground level back towards the equator
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Other cards in this set

Card 2

Front

What is a system?

Back

Any set of interrelated components that are connected together to form a working whole, characterised by inputs, stores, processes and outputs

Card 3

Front

What is a closed system?

Back

Preview of the front of card 3

Card 4

Front

What is an open system?

Back

Preview of the front of card 4

Card 5

Front

Why is the hydrological system closed?

Back

Preview of the front of card 5
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