geography - water and carbon cycles: the water cycle

what are systems?

a group of interrelated parts that work together by a driving process.

• a series of stores or components that have flows or connections between them.

what are systems composed of?

• inputs

• outputs

• stores

• flows

• boundaries

what are inputs?

where matter/energy is added to the system

what are outputs?

where matter/energy leaves the system

what are stores?

where matter or energy builds up in the system

what are flows?

where matter or energy moves in the system

what are boundaries?

limits to the system

what are open systems?

these are any system which has external inputs and external outputs of both energy AND matter.

what are closed systems?

these have transfers of energy both into and beyond the system boundary but NOT transfer of matter.

Planet Earth is generally considered a closed system, with energy coming from the sun, balanced by radiant energy lost from the Earth.

what is a cascading system?

the transfer of mass and energy along a chain of component subsystems, such that the output from one subsystem becomes the input for the adjacent subsystem.

River sediment cascades into the coastal zone for example.

 

what is a dynamic equilibrium?

when inputs equal outputs despite changing conditions

what is positive feedback?

enhances or amplifies an effect by it having an influence on the process which gave rise to it.

• often, this means that the consequences of the change are more severe.

what is negative feedback?

dampens or reduces an effect by it having an influence on the process that gave rise to it. 

• often means that the consequences of a change are less severe.

• often leads to dynamic equilibrium

what is the water cycle on a local scale?

an open system

what is the water cycle on a global scale?

a closed system

what are the 4 major stores of water?

lithosphere, hydrosphere, cryosphere and atmosphere

what is the lithosphere?

the inputs, flows and outputs all associated with the the crust and the uppermost mantle, which constitute the hard and rigid outer layer of the Earth.

• lithosphere is subdivided into tectonic plates.

what is the hydrosphere?

the inputs, flows and outputs all associated with the combined mass of water found on, under, and above the surface of a planet,

a discontinuous layer of water at or near the earth’s surface

what is the cryosphere?

the inputs, flows and outputs all associated with all of the frozen water in the Earth's system.

what is the atmosphere?

the inputs, flows and outputs all associated with the layer of gasses surrounding our planet

what is the global distribution of water?

• 97.5% of water is oceans and 2.5% if freshwater

• 2.5% - 79% is ice caps or glaciers, 20% is groundwater and 1% is easily accessible surface water

• 1% - readily accessible freshwater in lakes

what are the three main factors global freshwater supply is effected by?

Geology – This affects where water is stored and the location of aquifers and groundwater
Climate – influences the availability of rainfall, snowfall and rates of evaporation.  Climate can vary over time, with wetter and drier periods, hotter and colder periods.  This can affect water availability.
Rivers – which move or transfer water across river basins

what is atmospheric water?

consists of groundwater, soil, moisture, lakes, wetlands and rivers.

what is cryospheric water?

the water locked up on the Earth’s surface as ice

what is oceanic water?

water found in the atmosphere; mainly water vapour with some liquid water (cloud and rain droplets) and ice crystals.

what is terrestrial water?

the water contained in the Earth’s oceans and seas but not including such inland seas as the Caspian Sea.

how many categories of terrestrial water are there?

4

what are the 4 categories of terrestrial water?

• Surface water

• Ground water

• Soil water

• Biological water

what is surface water?

the free-flowing water of rivers, as well as the surface water stores of ponds and lakes.

what is ground water?

is water that collects underground in the pore spaces of rock up to a depth of 4km.

why is the amount of groundwater rapidly reducing?

extensive extraction for use in irrigating agricultural land in dry areas

how are the world’s water sources mainly distributed?

majority of stores are in:

• Northern & eastern Europe

• Throughout Indonesia and eastern Australia.

• Northern & central Africa

• Throughout South America

what is melting?

water going from a solid to a liquid

• extra energy needed

what is freezing?

water going from a liquid → solid

• loss of energy

what is evaporation?

water going from liquid → gas

occurs when energy from the sun hits the surface of the water/land and causes liquid to change from liquid to gas.

what is condensation?

water going from a gas → liquid

• loss of energy to atmosphere

what is sublimation?

water going from solid → gas

• extra energy needed

• substance has a 2-phase change

what is deposition?

water going from gas → solid

• loses energy

• 2-phase change

what are all the cryosphere stores of water?

• sea ice

• ice sheets

• ice shelves

• permafrost

• ice caps

what is sea ice?

ice that floats at the surface of our seas and oceans. 

• extent of ice varies between summer and winter,

• sea ice reflects a lot of solar energy back to space as it has a high albedo (a measure of surface reflectivity).  Without this ice, more solar energy is ABSORBED in these regions rather than reflected.

• Sea ice tends to freeze at temperatures slightly below 0°C because of the salinity of sea water.

what are ice shelves?

another type of sea ice – they are platforms of ice where ice sheets and glaciers extend out over the oceans from the land. 

• are common in Antarctica and when the separate from the main ice sheet they become ice bergs.

what are ice sheets?

these are a mass of glacial land ice extending more than 50,000km².

• the Antarctic ice sheet is one of the two polar ice caps of the Earth.

what is permafrost?

this is soil, rock or sediment that is frozen for more than two consecutive years → thickness of this layer varies

permafrost generally was created during previous ice ages and is now under threat of melting due to global warming - has the potential for a positive feedback loop as melting permafrost releases methane, a highly potent greenhouse gas.

what are ice caps?

these are smaller than ice sheets and are a mass of ice that covers less than 50,000 km³ of land area (usually covering a highland area). 

• found in mountainous areas and are the source areas for many of the worlds valley glaciers. 

• glaciers occupy many of the world’s valleys and their meltwater is significant as a water source for millions of people.

what can terrestrial water be sorted into?

• surface water

• ground water

• soil water

• biological water

what is soil water?

water which is held, together with air, in the unsaturated upper layers of soil.

what does soil water effect?

•Weather & climate

•Surface runoff potential (leading to flooding)

•Soil erosion

•Slope failure

•Reservoir levels

Water quality

what is biological water?

makes up the water stored in plants (biomass).

how is water transferred and stored in plants?

Plants/trees take in water through their roots.  This is transported to and stored in the trunk/branches

Water is then lost by transpiration through the stomata on the underside of leaves.

how does water transfer and storage effect environments?

plants helps to regulate the climate in specific environments.

what is groundwater?

the water held in saturated strata below

what is soil water?

the free-flowing water of streams and rivers, and the water of ponds and lakes

what states does atmospheric water exist in?

all 3

why is atmospheric water vapour important?

it absorbs, reflects and scatters incoming  solar radiation, keeping the atmosphere at a temperature that can maintain life

what does the amount of water vapour air can hold depend on?

depends upon its temperature. 

what temperature of water vapour can hold the most air?

Cold air can’t hold as much water vapour as warm air, which results in air over the poles being quite dry, whereas air over the tropics is very humid

what does an increase in water vapour lead to?

an increase in atmospheric temperatures

• becomes positive

  feedback as a small increase in global temperature would lead to a rise in global water vapour levels thus further

  enhancing the atmospheric warming.

why can oceanic water stay liquid at temps below 0c?

it has dissolved salts

why are oceans becoming more acidic?

due to the increased absorption of carbon from the atmosphere.  This forms carbonic acid.

what aspect of earth water stays the same but what changes?

amount or mass of water on Earth remains fairly constant over time but the location of that water into the major reservoirs of saline water, ice, fresh water, and atmospheric water is variable and depends on a wide range of climatic variables.

what is surface runoff?

the unconfined flow of water over the ground surface

what is subsurface flow?

is the flow of water beneath Earth's surface as part of the water cycle

how can the water cycle influence temperature changes?

• when water evaporates → takes up energy from its surroundings = cools the environment.

• when it condenses → releases energy = warms the environment.

  → heat exchanges influence climate.

what does the water cycle start with?

water evaporating from the ocean

what happens after water evaporates from oceans in the water cycle?

warm moist air rises in thermals where it cools as it rises through the troposphere

what happens while the air rises in the water cycle?

air cools and loses its capacity to hold water vapour as its relative humidity rises, and condensation occurs releasing latent heat.

what happens after condensation occurs in the water cycle?

forms clouds at the dew point, and these clouds are blown inland. 

what happens after clouds form in the water cycle?

Relief features can force the clouds higher, water droplets collide with one another and get bigger, and eventually the droplets are big enough to fall to earth as precipitation. 

what happens in the water cycle after precipitation is formed?

can be stored on the surface as snow or ice, or can be intercepted by trees and vegetation.

what happens after precipitation has been intercepted in the water cycle?

• on the trees or vegetation the water can be dripped off leaves, flow down the vegetation as stem flow or be taken up and lost as transpiration. 

• could fall straight into the ground where it can percolate into the soil then infiltrate into the rock underneath if the soil and rock are permeable → if the rock is not permeable or the soil stores are full then surface runoff will occur. - water will then work its way through the soil (soil flow) or rock (through flow) or over the land and into streams and rivers.  These small tributary streams join together at confluences and the river will grow in size and strength.

what is residence time?

defined as the amount of water in a store divided by either the rate of addition of water to the store or the rate of loss from it.

what stores have a long residence time?

• ice caps and sheets have incredibly long residence times - water gets “locked up” in these stores and has to travel through the cryospheric system or wait for changing climatic conditions before it is released again. 

• oceans also store water for long periods of time, water can be transferred to incredible depths and remains in the oceanic store for long periods of time. 

which stores have shorter residence times?

• Surface sea and ocean water is recycled between stores more rapidly. 

• In the atmosphere the residence time of water vapour relative to total evaporation is only about 10 days - Water is rapidly moved in and out of this store via various processes in the water cycle.

what do the rates of evaporation depend on?

• Amount of solar energy
• Availability of water
• Humidity of the air - The more humid the air the closer to saturation point the air is so less evaporation will occur
• Temperature of the air – Warmer air can hold more water than cold air.

what does humidity measure?

how much water vapor is in a parcel of air at any given time.

what air holds more water vapour?

can hold more water vapour than cooler air, and this is a vital concept to understand when discussing the weather. 

where along the globe holds the most water vapour?

tropics - can hold much more water vapour than higher latitudes because the air is warmer throughout the year.

what is relative humidity?

this is the amount of water vapour in the air at a given temperature compared to how much the air could possibly hold at that temperature.

what does cloud formation require?

require “dirty” air, as it is the pollen and dust particles around which water droplets form. 

how does condensation nuclei create condensation/hail?

• these water droplets are tiny, and coalesce or collide to form larger droplets. 

• in the case of sub zero temperatures, it is ice crystals that form and join together in the ice crystal mechanism. when the water droplets or ice crystals in clouds grow to a certain size, gravity causes them to fall because of their own weight

what is precipitation?

any product of the condensation of atmospheric water vapor that falls under gravity

what is the importance of precipitation in the drainage basin?

the main input into the drainage basin system.

when does frontal rainfall occur?

where warmer air meets colder and the former is forced to rise

why does frontal rainfall occur?

warm air is rising → cools initially at the Dry Adiabatic Lapse Rate and then at the Saturated Adiabatic Lapse Rate as latent heat is released during condensation.

results in cloud formation and eventually rain (once the droplets have collided enough to be big enough to fall).

what is relief rainfall?

a major method of precipitation formation in the UK and relates to the precipitation that is created as air masses are pushed up and over mountainous or upland areas

where does relief rainfall fall?

where moist air is forced to rise over a physical barrier such as a mountain range.

what is convectional rainfall?

where the Sun's energy hots the surface of the planet which heats the air above → air then has extra energy and rises upwards in thermals. → heat energy also causes rapid evaporation and evapotranspiration = air rising is humid.

air cools as it rises + water vapour will condense once dew point is reached → large quantities of water vapour and fast condensation causes storm clouds. 

• results in towering cumulonimbus clouds

what is cryospheric processes?

are those processes that affect the total mass of ice at any scale from local patches of frozen ground to global ice amounts.

• have a direct impact on the major stores of water, they lock up water as ice from the hydrosphere lowering sea levels, or release water during melting in warm periods rising sea levels. 

how does ice form?

ice forms from the compression of falling snow.

layer upon layer of snow is added → exert a pressure on the snow at the base = compressing that snow and forcing air out of it. will slowly form a denser substance called Névé and eventually ice. 

• Melting and refreezing of previously fallen snow can also assist in this process.

what two variables effect ice mass?

1. Accumulation is the build-up of ice mass
2. Ablation is the loss of ice mass

what happens when the glacier is said to be in a steady state?

Where accumulation and ablation are equal

what happens when accumulation is greater than ablation in a glacier?

leading to growth in ice mass and potential glacial advance down the valley

what happens when ablation is greater than accumulation?

leading to a loss of ice mass and the potential retreat of the glacier up valley.

what months do accumulation and ablation occur in?

accumulation tends to be within the colder months and ablation within the warmer months.

how does ice move?

Ice can move in many ways → this is determined by the glacial mass balance + the temperature and precipitation regime of the area the glacier is found within.

•  It shifts ice into more temperate zones where it can melt and become part of the atmosphere or hydrosphere via meltwater. 

• It also moves ice to the edges of ice sheets by the sea where the ice can calve off to become ice bergs and melt into the oceans.

what is the drainage basin?

is the area of land drained by a river system (a river and its tributaries).

• it includes the surface run-off in the water cycle, as well as the water found in the ground.

what separates drainage basins?

watersheds

This is the area that separates on drainage basin from another, indeed, the water shed is the upper limit around the drainage basin.

why is a drainage basin an open system?

• it is open to inputs from outside, such as precipitation, and is responsible for outputs out of the system, such as output of water into the sea and evaporation of water into the atmosphere.

why is a drainage basin a cascading system?

as the outputs from drainage basins become the inputs to other systems such as the coastal system.

what does the drainage system start with?

starts with an input from the water cycle – precipitation, after the processes of condensation and cloud formation.