EQ1 Flashcards
what is the hydrological cycle
The global hydrological cycle is a closed system driven by solar energy and gravitational potential energy
what makes the hydrological cycle a closed system
It does not have external inputs and outputs so there is a fixed amount of water in the Earth
where is the water stored in the hydrological cycle
This water can exist in stores and move between these stores in a series of transfers
TRUE or FALSE when water is transferred between stores in the hydrological cycle it doesnt change matter ever
false
Some of these transfers involve a change in state, while others just a movement of water from one store to another
what are fluxes
Fluxes are the rates of flow between stores. The greatest fluxes occur over the oceans.
what are fluxes driven by
Fluxes are driven by precipitation, evaporation, cryospheric exchange and run off generation (both surface + ground water)
what are the 4 water stores
- ocean
- terrestrial
- cryosphere water
- atmosphere
what are the 2 types of terrestrial water stores
greenwater and bluewater
examples of greenwater
underground (soil)
vegetation
examples of bluewater
lakes
rivers
underground (aquifers)
what water stores have the longest residence times
groundwater and ice caps
what is residence time
Residence time = the average times a water molecule will spend in a reservoir or store
what is fossil water
ancient, deep groundwater from former wetter times, it’s not renewable or reachable for human use
why do some stores have shorter residence times
Some very accessible stores, such as soil moisture and small lakes and rivers have a much shorter residence time because it’s easily lost to other stores
what water store has the shortest residence time
Atmospheric water has the shortest residence times as it evaporates, condenses and falls to the Earth as precipitation within about 10 days
TRUE OR FALSE there is no link between pollution levels and residence times
FALSE
there is a link
Longer the residence times the more easily they are polluted as the water is in situ for a longer length of time
what is the water budget
It is the balance between precipitation, evaporation and run off
It can be useful at global, regional and local scales
what does the global water budget take into account
The global water budget takes into account all the water that is held in stores and flows of the global hydrological cycle
why are regional/local water budget useful
Water budgets at this scale provide a more useful indication of available water supplies
at a local water budget scale does it show:
A. convergence
B. annual balance between inputs and outputs
C. temperature
B
At a more local scale , water budgets show the annual balance between inputs (ppt) and outputs (EVT) and how this can impact soil water availability.
why are local water budgets so important
Soil moisture budget is a subsystem of the catchment water balance and is vital to agriculturalist
what is a catchment water balance
a record of the water volume that enters and leaves a catchment area over a period of time, as well as the change in water storage during that time
what is the water drainage basin budget formula
P = Q+E±S
P = ppt Q = discharge E = evt S = changes in storage
finish the sentence:
Soil moisture can either be in…
surplus, deficiency or recharge
what creates a soil moisture surplus
If precipitation exceeds evapotranspiration and the excess has not been used by plants
what creates a soil moisture deficit
when evapotranspiration exceeds precipitation there is a deficiency
what creates a soil moisture recharge
occurs when water is replaced after a dried period
TRUE or FALSE is the drainage basin a closed system
FALSE
its an open system
is the drainage basin a…
A. subsystem within the global hydrological cycle
B. a system within the soil moisture cycle
C. a subsystem within the global water budget
A. A subsystem within the global hydrological cycle
The drainage basin is a subsystem within the global hydrological cycle
External inputs and outputs cause what within the drainage basin
It is an open system as it has external inputs and outputs that cause the amount of water in the basin to vary overtime
on what sort of scale do variations of the drainage basin variations occur on
These variations can occur at different temporal scales:
→ hourly
→ daily
→ seasonally
→ annually
What is the drainage basin systems input
precipitation
what are the certain conditions that precipitation need to occur
- Air cooled to saturation point with a relative humidity of 100%
- Condensation nuclei, such as dust particles, to facilitate the growth of droplets in clouds
- A temperature below dew point ( point where there is no longer gas and must condense) - the temperature at which dew form, its a measure of atmospheric moisture
what are the three types of rain
convectional
cyclonic
orographic
where is convectional rainfall most common
tropical areas and in the UK summer
what creates convectional rainfall
when the land becomes HOT heating the air above expanding and rising, as it RISES it COOLS and its ability to hold onto water vapour DECREASES . Condensation occurs creating clouds and if the air continues to RISE rain will fall
when does cyclonic rainfall occur
when WARM air is forced to rise over dense COOL air.
as it rises the air cools and its ability to hold water vapour DECREASES
COndensation occurs and clouds and rain form
when does orographic rainfall occur
when air is forced to rise over a barrier e.g mountain
it cools and condensation takes place forming rain.
when orographic rainfall occurs the leeward (downwind) slope receives
LOTS of rainfall
OR
LITTLE rainfall
bonus points: this is known as the ___ ___ effect
little rainfall
this is known as the rain shadow effect
what are the factors influence precipitation on the drainage basin within the hydrological cycle
- Amount of precipitation
- Type of precipitation
- Seasonality
- Intensity of precipitation
- Variability
-The distribution of precipitation within a basin
how does the amount of precipitation influence precipitation on the drainage basin
the amount of precipitation, has a direct impact on drainage basins discharge
how does the type of precipitation (rain, snow, hail) influence precipitation on the drainage basin
snow acts as a temporary store, large fluxes of water released into the system after a period of rapid melting
how does the seasonality influence precipitation on the drainage basin
strong seasonal patterns of rainfall or snowfall will have a major impact on the physical processes operating in the drainage basin
how does the intensity of precipitation influence the drainage basin
intensity impacts flows on or below the surface. It is difficult for rainfall to infiltrate for example if it’s very intense as soil capacity has exceeded
how does the variability of precipitation influence the drainage basin
variability can be seen in 3 ways
- secular variability happens long term, e.g climate change trends
- Periodic variability happens in annual, seasonal, monthly or diurnal (day+night) context
- Stochastic variability, results from random factors e.g localization of thunderstorm
how does the distribution of precipitation within a basin influence the drainage basin
Large drainage basins catch more precipitation so have a higher peak discharge compared to smaller basins.
what are the flows and transfers of the drainage basin
Interception
Infiltration
through flow
overland flow
percolation
saturated overland flow
groundwater flow
channel flow
what is interception
its the process where water is stored in vegetation
what are the 3 main components of interception
interception loss
through fall
stem flow
what is interception loss
This is water that’s retained by plant surfaces and later evaporated or absorbed by the vegetation and transpired.
when does interception loss occur
When the rain is light, for example drizzle, or if short duration, much of the water will never reach the ground and will be recycled by this process.
when does through fall occur
This is when the rainfall persists or is relatively intense, and the water drops from the leaves, twigs, needles etc
what is stem flow
This is when water trickles along twigs and branches and then down the trunk
factors affecting interception capacity
type of tree
seasons in deciduous
wind speeds
intensity and duration of rainfall
how does the type of tree affect interception capacity
dense needle coniferous trees allow greater accumulation of water
how does the seasons in deciduous forests affect interception capacity
summer months will have greater interception
how does the intensity and duration of precipitation affect interception capacity
when lots of rain falls the trees become saturated with water so less will be intercepted
how does the wind speeds affect interception capacity
water can be lost from trees leaves in the wind and more water can be evaporated off the leaves
what is infiltration
The movement of water from the ground surface into the soil
what is infiltration capacity
the maximum rate at which rain can absorbed by the soil
what 6 factors influence infilitration
duration of rainfall
antecedent of soil moisture
soil porosity
vegetation cover
soil surface and structure
slope angle
how does duration of rainfall affect infiltration
Infiltration capacity decreases with time through a period of rainfall until a more or less constant low value is reached
how does antecedent of soil moisture affect infiltration
The rate of infiltration also depends on the amount of water already in the soil (antecedent of soil moisture) as surface or overland flow will take place when the soil is saturated
what does antecedent of soil moisture even mean
the amount of water already in the soil
how does soil porosity affect infiltration
Whether the soil is mainly sand, silt, loam or clay - also influences porosity
E.g sandy soils capacity = 3-12mm/hr
E.g less permeable clays 0-4 mm/hr
how does vegetation cover affect infiltration
bonus points: explain why this has led to recent changes in areas liable to flooding
The type, amount and seasonal changes in vegetation cover are a key factor with infiltration being far more significant in land covered by forests (50mm/hr) or moorland (42mm/hr)
hence the recent drive to vegetate upland catchments that flow into areas liable to flooding
how does slope angle affect infiltration
e.g very steep slopes tend to encourage overland run-off with shallower slopes promoting infiltration
what is overland flow
This type of flow occurs when precipitation intensity exceeds
the infiltration rate.
Examples of when does overland flow occur
- there is an intense torrential storm
high levels of precipitation over a longer period of time - there is a release of very large quantities of melt water from snow
- the ground in hot arid climates become baked and unvegetated.
what is through flow
Refers to the lateral transfer of water down slope through the soil via percolines (lines of concentrated water flow between soil horizons and the river channel).
what are percolines
lines of concentrated water flow between soil horizons and the river channel
TRUE or FALSE through flow is faster than overland flow
FALSE
through flow is slower than overland flow, this transfer can occur quite rapidly in porous, sandy soil.
what is percolation
The transfer of water from the surface or from the soil into the bedrock beneath
what does the rock have to be for percolation to occur
The rock needs to be permeable either:
with joints e.g limestone
or
pores e.g chalk and sandstone.
where is percolation most likely to occur
This is much more likely to occur in humid climates with vegetated slopes.
what is saturated overland flow
The upward movement of the water table into the evaporation zone
when does saturated overland flow occur
After lots of heavy rain the ground becomes saturated and so any further rain that falls will have to flow OVERLAND.
what is groundwater flow
It is a very slow transfer of percolated water through permeable or porous rocks
why is groundwater flow important
It is important in maintaining a steady level of channel flow in varying weather conditions.
what is channel flow
This takes place in the river once water from the three transfers reaches it and directly from precipitation.
what are the drainage basin system output
evaporation
transpiration
evapotranspiration
channel flow
what is evaporation
The process by which moisture is lost directly into the atmosphere from water surfaces and soil.
In what situation increases evaporation rates
Evaporation increases in warm, windy and dry conditions.
what are the 8 climatic factors that influence the rate of evapouration
Temperature – most important
Hours of sunshine
Humidity
Wind speed
Size of the body of water
Depth of water
Type of vegetation cover
Colour of the surface (albedo)
what is transpiration
Is the biological process by which water is lost from plants through minute pores (stomata) and transferred to the atmosphere.
transpiration rates depend on?
- time of year
- type and amount of vegetation cover
- how much moisture there is in the atmosphere
- length of growing season
what is evapourtransipration
The combined effect of evaporation and transpiration. It represents the most important aspect of water loss to the atmosphere.
what is channel flow
The flow of water in streams and rivers to the sea /ocean
How does temperature influence the rate of evaporation
Higher temperatures increase the rate of evaporation
How does hours of sunshine influence the rate of evaporation
More hours of sunshine generally increase evaporation rates because of the sun’s heat
how does humidity influence the rate of evapouration
Higher humidity levels slow down the rate of evaporation.
how does wind speed influence the rate of evaporation
Wind speed helps evaporation by blowing suspended water molecules away from the liquid’s surface, allowing more room for water vapour.
how does size of body of water influence rate of evapouration
Increased surface area allows water molecules to absorb more heat energy from the environment, which helps them evaporate
how does the depth of water influence rate of evapouration
Shallow water body results in more evaporation as solar radiations can be effective throughout the depth of in case of shallow water body
how does color of the surface influence rate of evapouration
Darker coloured surfaces absorb more light and heat, which causes them to evaporate faster than lighter coloured surfaces
what are the inputs, flows and outputs that are influenced by human activity
Precipitation
Evaporation
Interception
Infiltration and soil water
Ground water
how has human activity influenced precipitation
cloud seeding
what is cloud seeding
the introduction of silver iodine pellets or ammonium nitrate, to act as condensation nuclei to attract water droplets
what is the aim of cloud seeding
The aim is to increase rainfall in dry areas
How has evapotranspiration been influenced by human activity
deforestation
artificial reservoirs behind dams
channelisation
how has deforestation influenced rate of evapotranspiration
reduces transpiration
how has artificial reservoirs behind dams influenced the rate of evapotranspiration
increases evaporation
how has channelisation influenced the rate of evapotranspiration
cuts down surface storage - decreases evaporation
how has interception been influenced by human activity
Its largely determined by vegetation type and density so deforestation and afforestation both have significant impacts
what is deforestation
the intentional removal of forests or trees from land to make it suitable for other uses
what are the impacts of deforestation on the drainage basin
-Reduction in evapotranspiration and an increase in surface runoff
-Increases flooding potential
-Decline in surface storage
-Decreases in lag time - speeds up the cycle
-Increase in sediment downstream
what is afforestation
new trees are planted or seeds are sown in an area where there were no trees before, creating a new forest
what are the impacts of afforestation on the drainage basin
-Reverse impact - trapping sediment and slowing the hydrological cycle by lengthening lag times
-However only true about 30 years after planting – due to compacted ground due to planting equipment and little cover by younger trees
why is infiltration and soil within the drainage basin influenced by human activity
Largely resulted in a change in land use
TRUE or FALSE
Infiltration is 5x greater under forests when compared with grassland
TRUE
how is the rate of infiltration influenced by farmland and its uses
Reduced interception
Increased soil compaction
More overland flow
Land use practises are also important
Grazing cows - leads to soil compaction so reduces infiltration
Ploughing - loosens and aerates soil so increases infiltration
how has human activity influenced groundwater within the drainage basin
Irrigation has lead to the decline in the water table
how does urbanisation effects hydrological cycle
Building activity leads to clearing of vegetation, which exposes soil and increases overland flow. Piles of disturbed and dumped soil increase erodibility. Eventually the bare soil is replaced by a covering of concentrate and tarmac, both of which are impermeable
The high density of buildings means that rain falls onto roofs and is then swiftly dispatched into drains by gutters and pipes
Drains and skewers are built, which reduce the distance that storm water must travel before reaching a channel. The increase in the velocity occurs because sewers generate less friction than natural pathways: sewers are designed to drain water quickly.
Urban rivers tend to be channelised with embankments to guard against flooding. When floods occur they can be more devastating as the river overtops defences in a very confined space
Bridges can restrain the free discharge of floodwaters and act as local dams for upstream floods
In extreme weather events urban areas are highly vulnerable. They manage flood control problems with a higher, quicker peak discharge, well as pollution problems from the storm water which washes off the roads, containing toxic substances
how can humans manage their influence on the drainage basin
Developing appropriate land use – forestry and moorlands in the upper areas
Managing development in the lower part of the catchment by land use zoning
Limiting building on the floodplains – making space to flood
Defend high value properties and installations against flooding
Low cost strategies that can be used in lower flood risk areas;
– Semi permeable surfaces for car parks
– High level wiring systems in houses
– Government develop affordable insurances
– Building regulations can be tightened to ensure flood proof property designs
