Water Flashcards
closed system
inputs and outputs are cycled and there are no loses or gains in the system
the water system is dynamic because it is continually changing through transitions
biosphere
the living system (plants and animals)
cry sphere
the ice system (ice sheets and glaciers)
residence times
how long water stays in a particular store
fossil water
water that is no longer being naturally replenished and it may have been stored for a long time
water stores and transfers
- nearly 2/3 of this water is stored in polar ice caps, snowpack and glaciers making it inaccessible for long periods of time. Has to melt
- low lying regions can form atmospheric rivers to transport water horizontally (high moisture and winds)
- clouds shield earth from the sun when there is heavy enough rain
- availability of water affects the type and abundance of vegetation
- when the air temperature is warmer it can hold more water
- only small amount available for human use
stores
- cryosphere
- ocean (most abundant 97%), residence time of 3600 years
- rivers and lakes
- groundwater
- atmosphere
- vegetation (least abundant, 0.0001%), residence time of one week)
- soil moisture
fluxes
- evapotranspiration
- ocean precipitation
- land precipitation
- surface flow (40(103km3)
- ocean evaporation (413(103km3)
what forces drive the system?
- solar energy- heats water causing it to evaporate and then condense and precipitate
- gravitational potential- earths gravitational pull is converted into kinetic energy, accelerating water through the cycle
future implications of water security
- water is generally considered a renewable resource but humans extract fossil water which isn’t recharged (e.g. the Sahara)
- climate change is altering the budget, the cryosphere is melting and increasing the proportion stored in oceans. many populations rely on glaciers to feed rivers
- global population is rising. currently around 7 billion but this is projected to ties to 10 billion by 2055
consequences of water scarcity
- conflicts (transboundary)
- drought and famine
- environmental refugees
- price of water increases
- more use of technology (e.g. desalination causing further carbon emissions)
orographic precipitation
relief rainfall
- caused when air is forced to rise and then 3Cs when it meets the land (esp mountains and hills)
- this is typical in the Lake District
frontal precipitation
- caused when warm air meets cold air and forces warm air to rise (3Cs)
- typical in the UK
convectional precipitation
-caused when moisture evaporates and rises when heated by the sun
saturated overland flow
-surface run off caused when soil is saturated
what are basin wide factors?
factors that affect the whole basin
- inputs
- flows
- outputs
basin inputs
- highest inputs found at the topics due to the ITCZ, maximum heating at the equator causes rain and sinking air at 30 degrees north and south. it migrates N and S as the earth tilts creating monsoons and tropical rain belts
- this results in convectional precipitation (average rainfall at its highest is Mawsynram, India with 11,873mm of rain per year)
- lowest precipitation inputs are found in stable areas of high atmospheric pressure (e.g. Atacarna desert receives less than 0.2mm of rain per year)
how do the continents affect basin inputs?
- the distribution of precipitation is influenced by continentality (distance from the sea), as continental interiors such as the Gobi desert in Asia of the Alice spring region in Australia are far from moisture of maritime air masses
- relief, such as mountains and prevailing winds complicate air patterns with more precipitation occurring where prevailing winds are forced to rise over higher altitudes, forming orographic precipitation
what is interception dependent on?
- vegetation and precipitation
- interception is greater when precipitation is light and of short duration as dry leaves have greater water storage capacity
- coniferous intercept more than deciduous as it is denser and does not lose leaves during winter
what factors affect infiltration capacity?
- slope gradient
- precipitation intensity
- vegetation cover
- soil and rock type
- water table depth
- how saturated the soil is (infiltration capacity, maximum rate that soil can absorb precipitation)
- once in the soil water moves both vertically and laterally by the process of through flow. This is a downslope movement aided by gravity.
what are the two types of overland flow?
saturated overland flow and infiltration excess overland flow
- saturated overland flow occurs when water accumulates in the soil until the water table reaches or ponds onto the surface (common when there are thin soils of moderate permeability)
- concavities near a stream or riverbank often have high moisture levels and can produce saturated overland flow early in rain storm cycle
- infiltration excess overland flow occurs when the rainfall intensity exceeds the infiltration capacity, so the excess water flows over the ground surface, delivering water to down stream river channels
percolation and drainage basin flows
- water fills spaces in permeable and porous rocks creating ground water storage and an aquifer
- this happens where the permeable layer lies above an impermeable layer so water can’t permeate any further and creating a saturated zone
- porosity = total volume of pore space (greatest in corse grain rocks like sandstone)
- perviousness= rocks like limestone have joints and bedding planes along which water can flow
- rate will also increase according to the angle of the rock strata as a steeper gradient will allow gravity to operate more effectively.
outputs of a drainage basin
- factors affecting evapotranspiration
- wind will increase the rate of evaporation by reducing the relative humidity and preventing saturation of the air
- soil moisture content will determine the amount available for transpiration
- vegetation cover will increase transpiration. vegetation with low albedo (reflectivity) such as dark forests will absorb more solar radiation, increasing evaporation
- higher temperature, more evaporation
- channel flow is the water collected to flow in a rivulet, stream or river. The discharge is dependent on the amount of precipitation falling directly into the channel
what is actual and potential evaporation?
- actual evaporation is the amount of evapotranspiration that takes place given the actual water availability
- potential evaporation is the amount of evapotranspiration that could take place given unlimited supplies of water in an environment
main factors affecting drainage basins
- precipitation
- relief
- temperature
- lithology
- wind
- continentality
- vegetation
how does over abstraction impact drainage basins?
- In some locations, ground water is abstracted from aquifers faster than it is replaced, causing reduced groundwater flow and a lower water table. For example, ground water is used to irrigate 40% of China’s farmland and provides 70% of the drinking water available for northern regions, leading to a loss of 2.5 billion cubic metres of water each year.
- In other areas, reduced industrial activity has increased groundwater storage amplifying the risk of groundwater flooding if the water table reaches land surface. This can increase the system’s output through processes like evaporation.
- Aral Sea dried up draining bodies of water and leading to breathing difficulties due to salt in the air
- groundwater conurbation in major UK conurbations as a result of reduced abstraction for industries
how can the creation of impoundments impact drainage basins?
- dams restrict the flow of a river, holding water in reservoirs behind built impoundments. This causes water to pool outwards, dispersing over a larger surface area than in a river and meaning that more water comes into direct contact with sunlight. Subsequently, more energy is transferred to water particles, increasing the rate of evaporation and leading to greater outputs from the drainage basin system.
- Lake Nassar behind the Aswan Dam in Egypt has lost approximately 10-16 billion cubic metres of water per year through the process of evaporation.
- can also have a direct impact on the drainage basin inputs as it means more moisture is retained in rainclouds, increasing precipitation levels.
- cause a river’s velocity to decrease. This is because, sediment carried in the river’s load is deposited in still water as there is a loss of energy. This means that the velocity is slower and so the rate of flows through the drainage basin will also decrease.
- e.g. Grand Canyon led to beach erosion as starved of sediment
how can deforestation impact drainage basins?
- rainforests add water to the atmosphere via interception and evapotranspiration. Here, this moisture then contributes to the formation of rainclouds increasing precipitation and therefore the system’s inputs. When forests are cut down less water goes into the atmosphere and rainfall declines sometimes leading to drought.
- less interception, decreasing processes like through flow and ground flow whilst increasing surface run off as there is less time for water to be absorbed by the ground. -Rainfall has a global affect, travelling around the world and therefore unlike more sever than other local factors. For example, rainforests in the Congo are shown to have affected rainfall in Midwest America.
how can urbanisation impact drainage basins?
creation of impermeable surfaces reduced infiltration snd surface run off increasing river discharge
-this increases flood risk in areas like Winchester and Mindhead in the UK
how can cloud seeding impact drainage basins
- attempts to change the amount of precipitation by dispersing substances into the air that serve as cloud condensation nuclei (hydroscopic nuclei)
- new technology and research claims to have produces results that makes it a dependable and affordable solution to water deficits in certain regions
- for many regions, effectiveness is being debated
- China used cloud Seeding before 2008 olympics in Beijing to clear the air of pollution
- used in Alpine Meadows Ski Resort, California to improve snow cover
- 2015 in Texas to combat drought
water budget equation
p= Q+E(+/-)S precipitation = discharge + evaporation (+/-) change to strores
soil moisture surplus
precipitation is greater than potential evapotranspiration and the soil water stores is full so there us a surplus of soil moisture for plant use, runoff and recharging groundwater.
-soil is at field capacity
soil moisture utilisation
potential evapotranspiration increases and exceeds precipitation, so there is more water evaporating from the ground surface and being transpired by plants than is falling as rain
-water is also drawn up from the soil by capillary action and the water is gradually used up
soil moisture deficit
- the soil water store has been used up by high rates of evapotranspiration and low precipitation
- plants can only survive if they are adapted to periods pf drought or are irrigated
soil moisture recharge
-this occurs when potential evapotranspiration decreases so that it is lower than precipitation and the soil starts to fill up again
field capacity
- the soil is now full of water and cannot hold any more
- further rain could lead to surface run off
potential evapotranspiration
-the amount of evapotranspiration that occurs as a result of temperature and vegetation (time of years) as long as there is water available
river regime
described the annual variations in discharge of a river at a particular point
-cumecs