Chapter 1- Water

What are open systems?

Systems that have external inputs and outputs of energy and matter exchange at its boundaries

What are closed systems?

Only have energy as its input and output, matter is contained within the system boundary

Is the global hydrological system open or closed?

Closed system- no external inputs or outputs, water is not lost or gained from space. 

What are the three main features of the hydrological cycle?

Evaporation
Condensation
Flows

How is the hydrological cycle powered?

Powered by the sun
Sun heats the water and evaporation occurs
Water vapour then rises into atmosphere and condenses to form clouds, drives atmospheric circulation
Cloud droplets fall back to earth as precipitation

How can the hydrological cycle influence local temperature fluctuations?

As water evaporates- uses energy from surroundings, cools the environment
Water condenses- heat is released, warming surroundings

What percentage of the world's freshwater is accessible to humans?

0.9%

Define store (of water)

A body of water that acts as a holding point

What are the main water stores?

• Oceans

• Rivers and lakes

• Dams and reservoirs

• Frozen water in the cryosphere (ice caps and glaciers)

• Groundwater in the lithosphere

• Water vapour in the atmosphere

Define and summarise annual flux

Annual flux- the variations in flows due to temperature, season and location
Flows e.g. evaporation- highest in warmer areas due to increased heating from sun, leads to high rates of precipitation at equator too. 

Define global water budget

The difference between inputs and outputs from different water stores

Define residence time

The time water is held in a store

What is the impact of climate on the global water budget

During last Ice Age- roughly 1/3rd of Earth's surface was covered in ice sheets and glaciers
Increased magnitude of cryosphere's stores
Lowered hydrosphere's stores and sea levels were over 100m lower than today

Summarise cryospheric processes?

Second largst store of water- ice (95% of this stores as ice sheets of Antarctica and Greenland)
Total melting of ice sheets could result in 60m sea level rise
Melting of ice sheets adds water to hydrosphere store of oceans
Ice shelves further destabilised causing further melting
Positive feedback loop

Define drainage basin/ catchment area

An area drained by a river and its tributaries

Define watershed

The boundary of a drainage basin

Are drainage basins open or closed systems?

Open systems- meaning they have inputs and outputs

What are the key features of a drainage basin?

Watershed
Source
Confluence
Tributary
Mouth

What are the different types of flows above and below ground?

Above:

• Throughfall
• Drip flow
• Trunk and stem
• Overland surface flow (channel flow or sheet flow)
• Interception (eg. by vegetation)

Below:

• Infiltration
• Throughflow
• Percolation
• Baseflow/ gorundwater flow

What are the key physical factors which influence drainage basins?

• Climate- type and amount of precipitation, extent of evaporation

• Soils- structure and type impacts infiltration and through flow, soil is permeable, saturates or frozen- low infiltration rates

• Vegetation- amount and type affects interception, infiltration and drip flow, more vegetation- greater amounts of flow, less vegetation- surface runoff increases

• Geology- impermeable or permeable rock- determines rates of percolation, also affects type of soil which impacts flows

• Relief- gradient of slope impacts on surface runoff, upland areas also experience more precipitation

What are the key human impacts on the drainage basin?

• Deforestation

• Changing land use

• Abstraction

• Reservoirs

• Urbanisation

How does deforestation impact the drainage basin?

Felling and clearance of trees reduces interception and infiltration rates, increasing surface runoff and reduces evapotranspiration which reduces precipitaiton

How does changing land use impact the drainage basin?

Link to urbanisation, agriculture- reduces amount of large vegetation, decreasing interception and increasing surface runoff, livestock farming can lead to compaction of soil reducing infiltration

How does abstraction impact the drainage basin?

Leads to reduces flow in rivers and reduces amount of groundwater

How do reservoirs impact the drainage basin?

Reduces water flow downstream, increases evaporation due to greater surface area of water

How does urbanisation impact the drainage basin?

Increase in area of impermeable surfaces, urban surfaces of tarmac and concrete are impermeable so reduce infiltration and increase surface runoff. Drainage systems move water to rivers more rapidly, increasing risk of flooding

Define water balance

The balance between the inputs and outputs of a drainage basin

How can water balance be shown in a formula?

P=O+E+S
P= precipitaiton
O= total runoff/ streamflow
E= evapotranspiration
S= changes in storage

How does the water balance change in the UK?

In general- water balance shows seasonal patterns
Wet seasons- precipitation is higher resulting in increased surface runoff, higher discharge and higher river levels, positive water balance
Dry seasons- evapotranspiration exceeds precipitation as plants absorb water, ground stores are depleted, produces water deficit, negative water balance

When/ how does soil moisture utilisation occur?

In summer- potential evapotranspiration exceeds precipitation so plants and animals utilise water in soil

Summarise soil moisture recharge

Water has been taken from the soil due to drought or being used by plants
In Autumn, water must be recharged resulting in little overland flow

Define field capacity

The amount of moisture held in the soil after excess water has drained away and infiltration has descreased. 

How is river discharge calculated?

Q=A*V
Q= Discharge in cumecs
A= Cross sectional area im m^2
V= Velocity in m/s

What are the two main types of hydrograph?

Annual (also known as river regime)
Storm

Define river regime

An annual hydrograph that shows the patter of seasonal variations that take place through a drainage basin to river discharge over a year

What are the key features of a flashy hydrograph?

Short lag time
High peak discharge
Steep rising limb

What are the key features of a flat hydrograph?

Long lag time
Low peak discharge
Gentle rising limb

What factors can lead to a flashy hydrograph?

Rock type- impermeable rock decreases percolation and increases surface runoff 
Soils- clay soils have low infiltration rate increasing surface runoff
Weather/ climate- heavy or prolonged rainfall and rapid snowmelt can exceed capacity of soil leading to surface runoff, low evaporation rates increases surface runoff

What factors can lead to a flat hydrograph?

Rock type- permeable rock allows percolation leading to lower surface runoff
Soils- sandy soils have high infiltration rate, decreasing surface runoff and increasing throughflow
Weather/ climate- Steady rainfall and slow thaw of snow that don't exceed the infiltration capacity of the soil, high evaporation rates lead to lower surface runoff. 
Vegetation- deciduous plants/ trees mean there are high rates of interception
Drainage basin size- large basins have longer lag times and gentler rising limbs as water takes longer to flow through basin
Human activity- link to urbanisation, afforestation or deforestation

What are the key factors impacting a drainage basin?

Relief
Climate
Vegetation
Geology
Soils

Define stores, fluxes and processes

Stores- stocks of water and places where the water is held e.g. oceans
Fluxes- the measurement of the rate of flow water between these stores
Processes- the physical factors which drive the fluxes of water between stores

What is the difference between blue water and green water?

Blue water- stored in riveres and lakes in liquid form
Green water- water which is stored in vegetation and plants

Define cryosphere

Areas of the Earth where water is frozen into snow or ice

Define fossil water

Ancient, deep groundwater from former pluvial (wetter) periods

Define groundwater flow

The slow transfer of percolated water underground through pervious or porous rocks

What is saturated overland flow?

Water runs over land and into rivers when ground already full of water during rainfall event

Define percolation

The movement of water under the influence of gravity from the soil into permeable rock below

Define throughflow

The movement of water through the soil and into a river

Define interception storage

Water held on surface of vegetation after interception (vegetation catching precipitation) water taken into structure of plants becomes vegetation storage

What are the main physical factors affecting the drainage basin?

Climate- amount of ppt determines input, warmer climate, more evaporation, less water reaching river
Soils- loose, permeable soils encourage infiltration
Relief- higher land, more rainfall, steeper slopes, faster overland flow
Vegetation- greater amounts, intercept more and encourage evapotranspiration, roots increase infiltration rates
Geology- permeability affects percolation + groundwater storage

How does abstraction affect the drainage basin?

Abstraction- pumping water from ground, reduces groundwater storage in aquifer and lowers water table

Summarise deforestation in the Amazon

20% of rainforest deforested due to logging and to make space for cattle ranches and farming
Local climates have been altered
Interception reduced, decreasing evapotranspiration, reducing precipitation long term
Overland flow increased, soil and silt carried into rivers, nutrients washed away

Explain how river regimes vary for different rivers

Key factors- climate, geology, land use 
Amazon- high precipitation through year, slight variation in drier winter season, small human impact from HEP
Yukon- high seasonal variability, low discharge in winter as water stored as snow and ice, summer snowmelt greatly increases discharge
Murray Darling- high variability due to seasonal variations and significant extraction for irrigation