1.B - the water cycle as a system Flashcards
what are the main stores of water?
- oceans
- polar ice and glaciers
- groundwater/aquifers
- lakes
- soils
- atmosphere
- rivers
- biosphere
how much water do the oceans store?
- 137,000 thousand cubic kilometers
- 97% globally
how much water does the land store?
- 39,000 thousand cubic kilometers
- 0.7% globally
what is worrying about the amount of water stored in polar ice and glaciers?
- as they melt due to global warming this will greatly increase the volume of water in oceans = SL rise = flooding
what challenges are there with most of the water being stored in oceans?
- 97% of water stored in our oceans
- salt water = toxic to most crops and also can’t be drunk by humans
- desalinisation is very expensive and quite inefficient
what are aquifers?
water bearing bands of porous/permeable rock
what are ice sheets?
floating sheets of ice permanently attached to a land mass
what are the flows in the water cycle system?
- evapotranspiration
- precipitation
- ablation
- infiltration
- run off
- groundwater flow
define evapotranspiration
combined loss of water at the surface through evaporation and transpiration by plants
define precipitation
moisture (rain, snow, hail) falling from clouds towards the ground
define ablation
the loss of ice and snow, especially from a glacier, though melting, evaporation and sublimation
define infiltration
the vertical movement of rainwater through the soil
define run-off
the movement of water across the land surface
define ground-water flow
the horizontal movement of water w/in aquifers
what does condensation refer to?
- condensation refers to the change of state from water vapour into liquid water.
- clouds form as a result of condensation in the atmosphere.
- this will happen when air is cooled so that it reaches its dew point.
in what ways does air reach the dew point?
- it can occur when air rises upwards due to being warmer than surrounding air (convection). As the air rises, its pressure drops and it expands and cools until its dew point (adiabatic expansion)
- air can be forced to rise over mountain barriers and so again it cools by aidiabatic expansion as it rises
- air may also be forced to rise as it meets colder air at a front
- finally if a mass of air will cool if it moves across a relatively cooler surface (advection). this may happen as air moves from sea to land in the winter
what is a cumuliform cloud?
- flat bases and considerable vertical development
- form when air is heated locally through contact w/ the Earth surface
- this causes heated air parcels to rise freely through the atmosphere (convection), expand (due to the fall in pressure w/ altitude) and cool
- as cooling reaches the dew point, condensation begins and clouds form
how do cumuliform clouds form?
- form when air is heated locally through contact w/ the Earth surface
- this causes heated air parcels to rise freely through the atmosphere (convection), expand (due to the fall in pressure w/ altitude) and cool
- as cooling reaches the dew point, condensation begins and clouds form
what is a stratiform cloud?
- develop where an air mass moves horizontally across a cooler surface (often the ocean)
- this process, together with some mixing and turbulence is known as advection
what is a cirrus cloud?
- wispy, cirrus clouds which form at high altitude, consist of tiny ice crystals
- unlike stratiform cloud and cumuliform clouds, they don’t produce precipitation and therefore have little influence on water cycle
what is precipitation?
- precipitation is the water and ice that falls from clouds towards the ground (e.g rain, snow, hail, sleet and drizzle)
- it forms when the atmosphere can no longer hold water as vapour and additional water vapour reaches its dew point to form clouds.
- eventually these droplets of water/ice coalesce to form precipitation
- generally, warmer climates allows more vapour to be condensed, form clouds and precipitate.
- when it is cold, there is not as much energy for evapotranspiration, thus less clouds/precipitation
how does temperature affect precipitation?
- generally, warmer climates allows more vapour to be condensed and form clouds and precipitate.
- when it is cold, there is not as much energy for evapotranspiration, thus less clouds/precipitation
how does precipitation affect rivers?
- the type of precipitation and when it falls can also influence the nature of a river regime, which shows how much water is flowing in a river throughout a year.
- for example in some parts of the world such as East Africa or the Mediterranean, rain may only fall in the rainy season and so this may be the only time you see rivers flowing.
- summer = more glacial melt
what influences the flow of a river?
- interception storage capacity, wind speed, vegetation type, tree species (coniferous all yr round, decidous cant intercept rainfall in winter)
- vegetation = interception. mitigate against flooding. also bind the soil together = its not eroded into the river and won’t build up river capacity = less flooding
- rock type (permeable or not). impermeable rock = flashy rivers.
- steepness of valley/relief = high levels of surface run off if sides are steep. will impact speed of runoff and throughflow
- climate/time of year
- people = tarmac/urban areas increases river flow = erosion of banks end up in river channel = decreased capacity
- the amount and type of precipitation = heavy rain will saturate the ground quickly = icnreased SRO and river flow
mountain climate
snow melt in april to june causes high rates of discharge. during winter precipitation falls as snow, causing a low rate of discharge
humid tropical climate
- wet and dry seasons with high temperatures and heavy rainfall
- soils become saturated in the rainy season and cause rapid overland flow
- in the dry season the clay dries out quickly due to high evaporation
temperate climate
- rain falls throughout the year.
- vegetation and deep soils promotes through flow and groundwater flow
- lower precipitation and higher evapotranspiration in summer reduce discharge
mediterranean climate
- dry and hot summers often cause rivers to dry up or flow at very low levels.
- storms in winter can cause rapid increases in discharge
equitorial climate
two wet seasons, one in April/May and the other in October/November
what is the drainage basin?
- the river, its tributaries and the land that surrounds
- the drainage basin can be thought of as an open system when isolated from the atmosphere and sea.
what is the hydrological cycle?
- part of the global water cycle
- it describes the continuous movement of water on, above and below the surface of the Earth, usually within a drainage basin
drainage basin flows
- throughfall stemflow
- infiltration
- percolation
- surface runoff
- throughflow
- groundwater flow
drainage basin outputs
- transpiration
- evaporation
- river runoff
drainage basin inputs
- precipitation
drainage basin stores
- vegetation
- interception
- surface storage
- soil water storage
- groundwater
- channel storage
example of a negative feedback loop
- increase in surface run-off = trees and vegetation intercept more water to increase soil capacity and prevent flooding
what is evaporation?
- phase change of liquid water to vapour
- main pathway by which water enters the atmosphere
how does evaporation transfer heat around the planet?
- heat is needed to bring about evaporation and break the molecular bonds of water.
- but this energy input doesn’t produce a rise of temp in the water
- instead the energy is absorbed as latent heat and released later in condensation.
- this process allows huge quantities of heat to be transferred around the planet (explains how tropical storms can be so powerful)
in which 2 ways can rain falling to the ground reach rivers?
1.INFILTRATION - by gravity into the soil and lateral movement or THROUGHFLOW to stream and river channels
2.OVERLAND FLOW - across the ground surface as a sheet or as trickles/rivulets to stream and river channels
what is saturated overland flow and why is it important for flood risk?
- overland flow only occurs when soil becomes saturated and the water table rises to the surface = saturated overland flow
how does the permeability of rocks affect the catchment hydrology?
- where soils are underlain by permeable rocks, water seeps or percolates deep underground
- this water then migrates slowly through the rock pores and joints as groundwater flow and eventually emerges at the surface as springs
where and when is meltwater a significant contributor?
- meltwater is an important component of river flow in high latitudes and mountain catchments in spring and summer.
- rapid thawing of snow in upland Britain in winter is a common cause of flooding in adjacent lowlands.
what type of system is the global water cycle?
- CLOSED
- there’s no water entering/leaving the planet
why is it important for us to measure water cycle changes?
- flooding/natural disasters
- ↑ in wave energy = ↑ erosion in places
- positive feedback loop - reduction in ice cover = ↓ albedo effect = temp ↑ = more ice melts, loop continues
what is the hydrological cycle?
- part of the global water cycle
- it describes the continuous movement of water on, above and below the surface of the earth, usually within a drainage basin.
- the water moves from the atmospheric store into a drainage basin and exits the drainage basin when it enters the sea.
