Edexcel A-Level Geography Water

Define a flow

transfers of water between stores

Define a flux

the rate of flow between stores

What percentage of water is found in the ocean store?

96.5%

What percentage of water is found in the cryosphere store?

1.7%

What percentage of water is found in the groundwater store?

1.7%

What percentage of water is found in the surface water store?

0.01%

What percentage of water is found in the atmosphere store?

0.001%

What percentage of water is found in the biosphere store?

0.0001%

What is the global hydrological system driven by?

solar energy and gravitational potential energy

Describe the flow of evaporation

water turns from a liquid to a gas as a result of gaining solar energy. surface water to atmosphere

Describe the flow of condensation

water turns from a gas back into a liquid due to a loss of solar energy as a result of a decrease in temperature. atmosphere to surface water

Describe the flow of precipitation

when water falls from the sky due to gravitational potential energy. atmosphere to surface water

Describe the flow of ablation

melting of the cryosphere due to an increase in solar energy. cryosphere to surface water

Describe the flow of accumulation

the build up of the cryosphere store as water turns from a liquid to a solid. surface water to cryosphere

Describe the flow of transpiration

biological process by which water vapour is released through the stomata of plants. biosphere to atmosphere

What are the spatial factors that affect fluxes

latitude, air pressure, air saturation

How does the spatial factor of latitude affect the flux of evaporation?

locations closer to the equator receive more concentration sun’s rays, more solar energy, liquid turns to a gas. Most: sub-tropics 15-30 degrees N/S, lowest: poles

How does the spatial factor of air pressure affect the flux of precipitation?

locations that receive low pressure as a result of GAC receive more precipitation - Amazon rainforest is low pressure with high precipitation

How does the spatial factor of air saturation affect the flux of evaporation and precipitation?

air can only hold a certain amount of water at a given temperature, this is its saturation point. warm air can hold more moisture than cold air so warmer air masses lead to more evaporation and more water moving from the surface water to the atmosphere. when that air cools and condenses, more intense precipitation occurs

For every 1 degree increase in temperature, the air’s moisture holding capacity increases by what percentage?

7%

What temporal factors affect fluxes?

short term seasonal changes and long term seasonal changes

How does the temporal factor of short term seasonal changes affect the flux of ablation and accumulation?

in winter, temperatures are cooler so accumulation will exceed ablation and water moves from ocean to cryospheree. e.g. accumulation exeeds ablation in Canadian winters whereas in summer ablation exceeds accumulation

How does the temporal factor of long term glacial periods affect the flux of accumulation, ablation, evaporation and precipitation?

during glacial periods, average global temps are much lower so accumulation exceeds ablation leading to a larger cryosphere store and a smaller surface water store and there is less evaporation and precipitation due to more cold air

define ‘residence time’

the average time a water molecule will spend in a resevoir or store

how much water is there on Earth?

1.386 billion cubic kilometres

what is the residence time of oceans?

about 3600 years

what is the residence time of the atmosphere?

about 10 days

define a drainage basin

an area of land drained by a river and its tributaries. an open system within the closed system of the global hydrological cycle

define inputs

processes by which water enters the drainage basin

define flows

processes by which water moves within the drainage basin

define outputs

processes by which water leaves the drainage basin

what is a watershed

the boundary of a drainage basin which is usually a ridge of high land and divides and separates water flowing to different rivers

what are the inputs

precipitation

what are the flows

interception (throughfall and stem flow), infiltration, throughflow, percolation, groundwater flow, direct runoff, saturated overland flow

what are the outputs

evaporation, transpiration, interception loss, channel flow

what are the 3 types of rainfall

convectional, orographic, cyclonic

what is the key idea for the creation of precipitation

as air rises, it cools, reducing its ability to hold water vapour. the air reaches its saturation and dew points, leading to condensation around a condensation nuclei, forming clouds. when the water droplets on the condensation nuclei become too heavy, they fall to the ground due to gravitational potential energy

what causes convectional rainfall

solar radiation heats the ground, the ground heats the overlaying hair, the overlaying air expands, becomes less dense and rises (e.g. UK summer)

what causes orographic rainfall

air is forced to rise over a barrier such as a mountain (e.g. Scottish Highlands)

what causes cyclonic rainfall

a warm air mass meets a cold air mass. the warm air mass is lighter and less dense so is forced to rise over the cold air mass (e.g. most common type of rainfall in the UK)

Define interception

precipitation intercepted by vegetation via throughfall (leaves catch and drop precipitation) and stemflow (water trickles down plant stems)

define infiltration

water flows vertically into soils

define throughflow

water flows laterally through soils

define percolation

water flows vertically through rock

define groundwater flow

water flows laterally through rock

define direct runoff

waters flows overground

define saturated overland flow

water flows overground because soil saturation prevents further infiltration

define transpiration

loss of water vapour from plants stomata, movement from biosphere into atmosphere

define interception loss

loss of water from interception which evaporates into atmosphere

define channel flow

movement of water in a river

How does climate affect inputs, flows and outputs?

i: determines the amount, type and intensity of precipitation, higher temps lead to more evaporation which can cause convectional rainfall f: all fluxes depend on inputs, climate determines vegetation density and therefore the amount of interception, o: influences the amount and timing of water leaving the basin via river discharge, climate determines vegetation density therefore transpiration

How do soils affect inputs, flows and outputs?

i: antecedent conditions affect how much rainfall can be input into the soil via infiltration, soil type influences how much soil in input - sandy soils are permeable, infiltration capacity of 19-25mm/hour, clay soil is less permeable, infiltration rate of 3-8mm/hour, f: if soil is saturated, less infiltration so more saturated overland flow o: soils that store more water may delay outputs as water travels more slowly to the channel

How does vegetation affect inputs, flows and outputs?

i: dense vegetation intercepts more rainfall via throughfall and stemflow, vegetation can increase inputs into the drainage basin via biotic pumping, f: high vegetation density increases interception and infiltration, o: more vegetation, higher flux of transpiration

How does geology affect inputs, flows and outputs?

i: permeable rock e.g. limestone allows more input into the groundwater store via percolation, f: highly permeable rocks cause faster groundwater flow whereas opposite causes direct runoff, o: permeable geology delays outputs by storing water in groundwater aquifers

How does relief affect inputs, flows and outputs?

i: steep relief can cause orographic rainfall, f: steep terrain increases direct runoff and throughflow speed o: steep relief means more water reaches the channel more quickly increasing channel flow

What human activities disrupt drainage basin processes?

deforestation, land use change, creation of resevoirs, abstraction of water

how does deforestation impact drainage basin processes?

reduces amount of water that is intercepted. soil is more exposed in heavy rainfall, so soil compaction can occur, decreaseing the soil capacity so it becomes saturated more quickly leading to saturated overland flow, reducing biotic pumping due to less inputs of precipitation

how does land use change impact drainage basin processes?

urbanisation increases impermeable surfaces so there is more direct runoff, urban heat island effect can increase convectional rainfall by 10%, drains provide a direct and low friction route to the river increasing channel flow - Northwich urban sprawl within River Weaver drainage basin. agriculture compacts soil via cattle trampling and heavy machinery which reduces pore spaces and lowers the soil’s capacity, causing the soil to become saturated more quickly, leading to saturated overland flow

how does the creation of resevoirs impact drainage basin processes?

stores water that would naturally flow downstream, increased evaporation losses from standing water e.g. GERD dam in Ethiopia - concerns in Egypt about the amount of water held back

how does abstraction of water impact drainage basin processes?

reduces water in stores, during dry seasons even more water is abstracted, reduces channel flow, groundwater abstraction can lead to aquifer collapse, reducing water storage capacity. agriculture uses 70% of all freshwater globally

What is occurring in Amazonia (human disruption on drainage basin processes)?

17% of forest has been deforested, mostly due to cattle ranching and soy farming. Dry season in the Amazon is lasting 4 weeks longer in areas experiencing the most deforestation

What is the equation for calculating water budgets?

P=E+Q±S p= inputs, e+q=outputs, s=stores

What does a water budget show

how much water enters and leaves a drainage basin and how the stores change over time

When is a water budget positive?

when there is more water entering the drainage basin than leaving it during a specific time

When is a water budget negative?

when there is more water leaving the drainage basin than entering it during a specific time

What are the 4 different stages that the soil moisture budget can be in?

soil moisture surplus, soil moisture utilisation, soil moisture deficit, soil moisture recharge

what is soil moisture surplus?

when precipitation exceeds evapotranspiration and the soil moisture store is full and there is a surplus for plants to use

what is soil moisture utilisation

water is in the process of being used by plants or lost by evaporation

what is soil moisture deficit?

evapotranspiration exceeds precipitation. the soil starts to dry out

what is soil moisture recharge?

rain starts to fill the soil back up again

What happens to water budges in hot temperatures with high precipitation?

inputs are high, outputs are high, ideal conditions for vegetation growth so biosphere store increases, groundwater is protected from evaporation, water budget may be negative or positive

What happens to water budges in cold temperatures with high precipitation?

high inputs, low outputs, water budget will be positive as inputs exceed outputs so stores increase e.g. Canada

What happens to water budges in hot temperatures with low precipitation?

inputs are very low, outputs are very high, water budget is negative, surface water decreases, vegetation struggles to grow

What happens to water budges in cold temperatures with low precipitation?

inputs low, outputs low, water may be locked in the cryosphere, water budget may be positive or negative

define a river regime

the annual pattern of a river’s discharge

What are the two types of river regime?

steady (gradual fluctuations in discharge) and volatile (rapid fluctatuations in discharge)

Does the Amazon river have steady or volatile river regime?

steady

Does the Yukon river have steady or volatile river regime?

volatile

Does the Indus river have steady or volatile river regime?

volatile

How does climate impact a river regime?

Amazon: high levels of rainfall but high interception and infiltration due to thin soils and sedimentary rocks. Yukon: low discharge in winter but rapid in summer due to snowmelt. soils prone to permafrost which is impermeable. Indus: monsoon climate with summer rainfall so high discharge in the summer. glacial melt in spring. very seasonal flow

How do soils impact a river regime?

Amazon: mostly thin soils which saturate quickly but forest canopy increases interception. Yukon: permafrost soils so direct runoff due to impermeability. Indus: dry, compact soils so low infiltration, high saturated overland flow.

how does geology impact a river regime?

Amazon: mostly permeable sedimentary rock which allows percolation and increases groundwater flow. Yukon: bedrock mostly impermeable igneous so direct runoff. Indus: impermeable bedrock and steep relief promotes direct runoff/saturated overland flow

Describe a flashy storm hydrograph

short lag time, steep rising limb, high peak discharge, bankfull discharge exceeded

Describe a delayed storm hydrograph

long lag time, gentle rising limb, low peak discharge, bankfull discharge not exceeded

What effect does basin size have on a storm hydrograph?

smaller basin, precipitation has less distance to travel to reach the river, water reaches the channel more quickly reducing lag time, steeper rising limb, water reaches the river at a similar time increasing peak discharge. flashy hydrograph

What effect does basin shape have on a storm hydrograph?

at round basins all points are roughly equidistant from the centre of the river. creates a short lag time with a violent flash flood. when it rains all water reaches the river at the same time, increasing peak discharge. flashy hydrograph

What effect does drainage density have on a storm hydrograph?

high drainage density means there is a large surface area of the drainage basin covered by tributaries. input of rainfall reaches the main river channel more quickly as channel flow is faster. more water arrives at the same time increasing peak discharge. flashy hydrograph

What effect does rock type have on a storm hydrograph?

impermeable rocks don’t allow percolation. if there is overlying permeable soil it will saturate more quickly so more water reaches the river channel quickly via saturated overland flow. if no overlying soil, direct runoff. water reaches the main channel at the same time increasing peak discharge - flashy hydrograph

What effect does soil type have on a storm hydrograph?

less permeable soils (e.g. clay 3-8mm/hr) less water can infiltrate, saturates more quickly, saturated overland flow reduces lag time. more water reaches the river at the same time increasing peak discharge. flashy hydrograph

What effect does relief have on a storm hydrograph?

steep slopes - fast direct runoff so less time for infiltration and percolation. water reaches the river more quickly and at the same time increasing peak discharge. flashy hydrograph

What effect does vegetation have on a storm hydrograph?

less vegetation, less interception, intense rainfall can cause soil compaction, decreases infiltration capacity of the soil, more likely to reach saturation more quickly, saturated overland flow moves water quickly to the river. high discharge, flashy hydrograph

What human factors affect the shape of a storm hydrograph?

urbanisation, deforestation, agriculture

How does urbanisation affect a storm hydrograph?

impermeable surfaces don’t allow infiltration so water travels quickly via direct runoff, reaches the river at the same time, high peak discharge, flashy hydrograph

How does deforestation affect a storm hydrograph?

less vegetation, less interception, soil compaction decreases the infiltration capacity of the soil, saturated more easily, saturated overland flow increases peak discharge, flashy hydrograph

How does agriculture affect a storm hydrograph?

heavy machinery, cattle and ploughing causes soil compaction, decreases infiltration capacity of the soil, more likely to reach saturation faster - saturated overland flow increases peak discharge, flashy hydrograph

Explain the Northwich case study

Gowy-Weaver basin. 2021 Storm Christoph brought heavy rain but didn’t overtop the town’s £7 million flood defences. low laying, heavy clay soils, antecedent conditions were exceptionally wet, River Weaver straighted and widened for navigation purposes, flood defences present

How can planners manage flood risk and storm hydrographs?

limit building on floodplains, encourage green infrastructure, use permeable materials in urban design (Jodrell Bank car park), implement sustainable drainage systems, protect and restore natural vegetation, light surfaces tor reduce the albedo effect

define meteorological drought

a lack of precipitation compared to multi-year averages

Define drought

drought is a long-term shortage of water compared to the multi-year average for a reason

define hydrological drought

when rivers, lakes, resevoirs or groundwater storage levels fall below normal. this is often caused by a meteorological drought