Water Flashcards
closed system
the amount of water is kept the same and just circulated continuously
inputs
the movement of matter or energy into a system for example precipitation from the atmosphere into the ground or the sea
outputs
the movement of matter or energy out of a system so for example evaporation from the land or sea into the atmosphere
stores
where water is stored
water is stored for long periods of time in oceans (3600 years) and as groundwater (up to 10000 years)
flows
the amount of matter or energy transferred from one place to another
what does solar energy cause?
heat energy from the sun causes changed in the state of water and drives some of the processes such as evaporation
gravitational potential energy
the mass of the earth exerts a pull ok water causing water to fall as precipitation and refuses to flow downhill back to the ocean (the main store)
diagram of the hydrological cycle
what are some examples of water stores and what are their residence times?
why are some stores considered to be non-renewable?
because they are not replaced in a short period of time
for example:
– Fossil water was stored underground in rocks are very long time ago when the climb of an area was much wetter
describe the annual global fluxes diagram
what is the global water budget?
the annual balance between the fluxes sand size of water stores is known as the global water budget
why is water generally considered to be a renewable resource?
Because there is a constant circulation and replenishment of stores without any losses from the planet
how can the availability of water change throughout a year?
if there is a dry season or the climate in summer is hotter than normal then transpiration and evaporation rates may be higher
what is transpiration
the evaporation or loss of water from a plant mainly through its stomata
why do people need water
it is essential to lose and also used for farming, industry and cooling machinery
what is orographic rainfall
– Relief rainfall
– cause when humid air is forced to rise over mountains
– when the air calls higher altitude, moisture condenses forming clouds and droplets of water which then fall due to gravity
– most rain falls on the slopes facing the direction direction and top of the mountains with dry air on the other side (Lee) so less rainfalls (rain shadow)
what is frontal rainfall
– Course when humid air is forced to rise at a warm front or cold front line
– usually as part of a depression (low pressure system)
– again, the air calls, condensation takes place, clouds of water droplets form which has followed by rain
what is conventional rainfall?
– Cause when the ground and lower atmosphere are heated by the Sun causing rising air.
– humidity in the air condenses when it cools at high altitudes, forms towering culo nimbus clouds, often followed by intense heavy rainfall (thunderstorms)
what is interception?
when a layer of vegetation covers the ground and do intercepts rainfall before it can reach the ground
what is infiltration?
the movement of water downwards through spaces in the soil; this continues until capacity is reached and the soil becomes saturated
what is throughflow?
the movement of water downslope through the soil towards base level (river, lake or sea)
what is surface run off?
rain falling onto the ground may flow over the surface when it is so intense that there is no time for it to infiltrate
what is saturated overland flow?
if all soil spaces are full of water, then any further rain infiltrate and so will run off the surfacr
what is percolation?
the movement of water downwards through porous or permeable rocks?
what is groundwater flow?
the downwards and sideways movement of water in rock layers under the influence of gravity and rock structure
what are the 3 outputs?
evaporation
transpiration
channel flow
what is channel flow
run-off moves to the lowest points in a landscape where it collects to form a linear body of water flowing over the ground. The larger the amount of water, the larger the discharge.
what are the influences of physical factors on the hydrological cycle?
what human factors can disrupt the hydrological cycle?
deforestation
land use change
reservoir creation
abstracting water
how does deforestation effect the hydrological cycle?
removal of tree cover reduces interception and evapotranspiration, increasing surface run-off, soil erosion, and flooding during intense rainfall.
how does land use change effect the hydrological cycle?
natural vegetation absorbs more water than urbanised permeable surfaces which increased run-off and flow creating higher discharges and more flooding
how does reservoir creation change the effects of the hydrological cycle?
damming a river prevents channel flow, reducing discharge, downstream, and creating an evaporation source.
how does abstracting water change the hydrological cycle?
people use water for several purposes and sometimes this is taken from the surface all the ground faster than it is replaced meaning natural ways for water to leave an underground aquifer for example like rivers or springs will be affected
what is a water budget?
an account of the water stored in a system, such as a watershed, and the movement of water in and out of that system, annually
what is the water budget equation?
precipitation = channel discharge + evaporation +/- storage
P = Q + E +/- S
what does the water budget equation do?
– Allows a calculation of water supply during a year and identification of time periods when there may not be enough to meet natural and human needs
– When precipitation is greater than channel discharge and vapo transpiration there is a positive water balance when precipitation is less than channel discharge and evapotranspiration, there is a negative one.
what is soil moisture and why is it important?
– soil moisture is the amount of water in the soil and it is important for successful plant growth.
– in an ecosystem it is important to have enough soil moisture so that plants support other trophic levels (feeding groups.
– it is most important that soil moisture is high during growth season (spring and summer)
how does land use affect patterns within river catchment areas?
– Land use affects the movement of water after precipitation, such as interception and absorption by forests or the impermeable surfaces of urbanisation.
– land use zoning can reduce risk by controlling building on flood planes.
Planners are also involved in decision-making about flood prevention and protection
what are the factors effecting river regimes?
what are the factors effecting storm hydrographs?
what is drought?
drought is classified by a number of factors:
- weather conditions may remain dry for a longer period than normal
- farmers may experience a decline in soil moisture levels
- water levels in rivers and reservoirs fall
- human demand for water is greater than supply
drought is a slow onset hazard affecting 10% of earths land area and 18% of the population
what are some short term causes of drought?
blocking anticyclones: the polar front jet stream may move up (north) meaning subtropical high pressure air can move into the space it has vacated. In the summer of 2018 this caused widespread drought across the UK.
reduced soil moisture levels: there may not be enough precipitation to soak into soils because plants use it quickly or there is higher evaporation
what are some medium term causes of drought?
El Niño Southern Oscillation (ENSO): ENSO cycles occur in the pacific ocean every 7 year roughly. During El Niño warm water moves closer to the Americas reducing rainfall in the western pacific. During La Niña warm water moves to the extreme west of the tropical pacific, reducing rainfall in western parts of the americas. These cycles are known to have global effects such as La Niña events causing drought in East Africa.
Hydrological: Reduced amounts of water in rivers or the ground may occur if precipitation is reduced in mountainous areas over several years, especially reducing the amount of snow melt.
What are some long term causes of drought?
Global atmospheric circulation: descending air between the hadley and ferrel cells and between the polar cells creates hot and cold deserts respectively, also affecting the areas around them where droughts are common
Climate change: evidence suggests that higher temperatures are changing atmosphere systems. Subtropical high pressure areas are getting stronger, which stops the seasonal movement of ICTZ (which causes droughts). Rainfall events have become more intense rather than spread out over time. Higher sea temps have changed evaporation and wind patterns which may cause rain bearing winds to fail and have changed ocean currents; where cold currents become stronger evaporation is reduced causing drier conditions
how do you interpret synoptic charts?
- dark lines with triangles of half circles are fronts, pointing in the direction of movement
- triangle = cold
- semi circle = warm
- fainter lines are isobars with a number indicating the pressure in MB
- H = high pressure centres (anticyclones)
- L = low pressure (depressions/extra-tropical cyclones)
how does human activity lead to drought risk? (what things do humans do that cause droughts?)
over-abstraction of surface water: taking too much water from rivers and lakes and not replenishing it with precipitation
over-abstraction of groundwater: taking too much water out of aquifer stores lowering the water table and making wells dry up
deforestation: reduces interception, absorption and evapotranspiration so that water is lost from local areas, making them drier and more susceptible to drought
climate change: emissions of greenhouse gases are accelerating global warming which is changing precipitation patterns
what are wetlands and how are they vulnerable to drought?
wetlands are a type of ecosystem that is largely flooded. they have adapted to this so conditions changing will make the ecosystem vulnerable. their capacity to act as a natural filter and above floodwaters will be reduced after repeated droughts.
other processes like the oxidation of soils will release carbon into the atmosphere and nutrients or pollutants may become dangerously concentrated. some species like birds will leave the area and plants may be lost.
what are forests and how are they vulnerable to droughts?
forests have an important role in the hydrological cycle as well as other natural cycles such as carbon
trees in forests are often large and so require a large amount of water, especially fast growing species like pine
drought slows growth and causes stress, potentially causing the trees to lose leaves and be unable to photosynthesis, this can take as many as 4 years to recover from
droughts also weaken trees so they are more vulnerable to insects such as pine beetles and diseases
trees dying off can also harm food chains
what’s a textbook definition of flooding?
In areas experiencing a lot of precipitation, flooding may be a possibility. It may be fast onset (flash floods) or slower onset. The most common form of flooding occurs when a river reaches and then exceeds bank full discharge; additional water cannot be contained within the channel and so spills over onto the surrounding land (flood plain).
what are some meteorological causes of flooding?
- intense storms
- heavy rainfall
- snowmelt
- prolonged rainfall
- monsoon rains
why do intense storms cause flooding?
they bring a lot of rainfall in a short period, which moves quickly meaning it’s unable to soak into the ground causing it to flow more quickly into channels leading to them overflowing their banks. If the water runs over baked grounds it can lead to flash floods.
why does snowmelt cause floods?
snow can accumulate to a considerable depth and the climate quickly warming up in the spring can cause it to start melting quite rapidly.
frozen ground underneath the snow and steep slopes can cause the water to flow quickly.
why does heavy rainfall cause flooding?
too much rainfall can prevent throughflow or groundwater flow from taking place so the excess water runs off the surface and into rivers
why does prolonged rainfall cause flooding?
persistent rainfall is often the result of several low pressure systems passing over an area causing a sequence of frontal rainfall. first the soil is saturated so that later rainfall cannot infiltrated. this causes run off to increase and quickly enter river channels causing floods.
why do monsoons cause flooding?
subtropical areas often have wet or monsoon seasons, especially areas where there’s land between a mountain and a warm ocean. Monsoon seasons are characterised by torrential rainfall which falls onto hard dry ground. This causes increased surface run off and then saturated ground meaning water flows faster into rivers, increasing levels until they flood.
what are the human influences on flooding?
land use change
floodplain use
hard engineering
why is land use change a human cause of flooding?
removal of natural vegetation and its replacement with impermeable surfaces causes changes in hydrological processes.
run off is increased from roofs or farmed land (impermeable surfaces).
soil erosion increases adding sediment to rivers channels, changing their shape and reducing capacity so that they flood with a lower discharge.
why does hard engineering increase flood risk?
bridges narrow river channels, reducing capacity and causing higher water levels upstream or suddenly downstream if a bridge collapses
artificial levees increase channel capacity but transfer more water downstream increasing flood risk, also, if they break they cause flash floods over a wide area
channelisation (straight concrete channels) transfer water more quickly downstream, increasing risk.
why does floodplain use cause increased flood risk?
floodplains are often drained for construction causing the land to shrink as it dries out, taking it below normal river levels and causing it to flood more easily
what are the environmental impacts of flooding?
- ecosystems: small floods can be beneficial as they help to replenish ecosystems but intense floods increase soil and river erosion and cause pollutants to get into water ways
- soils: become waterlogged on level ground or scoured away on slopes by increased surface flow. flood events reduce the microbial biomass in soil but in the long term more nutrient rich soils are provided.
What is a closed system?
The transfer of energy but not matter between the system and its surroundings
The same amount of water is kept in the system and just continuously circulated
What are inputs?
The movement of energy or matter into a system: in the hydrological cycle closed system, this is an internal movement into a store only
> precipitation from the atmosphere into the ground or sea
What are outputs?
The movement of matter or energy out of a system; in the hydrological cycle closed system, this is an internal movement only out of a store
> evaporation from the sea or land into the atmosphere
What are stores?
Where matter or energy is kept for a relatively long period of time; water is stored for long periods of time in oceans and as groundwater
What are flows?
The amount of water transferred from one place to another
> through flow and run off
What is solar energy and what does it cause?
Heat energy from the sun causes changes in the state of water and drives some of the processes in the hydrological cycle like evaporation and wind direction
What is gravitational potential energy and what does it cause?
The mass of the earth exerts a pull on water, causing water to fall as precipitation and rivers to flow back downhill to the ocean (the main store)
Why are some stores considered non renewable?
Because they are not replaced during a short time
> fossil water was stored underground in rocks a very long time ago when the climate of an area was much wetter
> melting of glaciers due to climate change reduces water stored in ice and likely won’t be replaced in the near future
What’s residence time?
The amount of time water spends in one store
What percentage of the total amount of water on earth does the oceans hold? What is its residency time?
96.9%
3600 years
What percentage of the total amount of water on earth does the cryosphere hold? What is its residency time?
1.9%
15000 years
What percentage of the total amount of water on earth does the groundwater hold? What is its residency time?
1.1%
More than 10,000 years
What percentage of the total amount of water on earth does the surface water hold? What is its residency time?
0.01%
2 weeks - 10 years
What percentage of the total amount of water on earth does the atmosphere hold? What is its residency time?
0.001%
10 days
What percentage of the total amount of water on earth does the biosphere hold? What is its residency time?
0.0001%
7 days
What is the global water budget?
The annual balance between the fluxes (flows) and size of water stores is known as the global water budget
Why is water generally considered to be renewable?
Becasue there is a constant circulation and replenishment of stores without any losses
Why may there be less water availible during certain times of year?
Dry seasons or in the summer when plant absorption and transportation and evaporation rates are higher
The amount of soil moisture may vary, which is important to plant growth and runoff and throughflow fluxes
Why do people need water?
For life as well as farming, industry, cooking machinery and HEP
What does the water budget determine?
What is availible because some regions or areas have more precipitation than others
Some have more rivers and lakes, some have more groundwater
Why can water budgets change in some regions?
Some stores are constantly replenished but others, like fossil water aren’t and the water may be experiencing change in a region due to global warming
What’s orographic rainfall?
When humid air is forced over mountains and cools at a higher altitude it condenses and form clouds. This causes rainfall on the slopes facing the wind direction and the top of the mountain with drier air on the other side so less rain falls.
What’s frontal rainfall?
Caused when humid air is forced to rise at a warm front or cold front, usually as part of a low pressure system. Again, the air cools, condenses and forms clouds of water droplets which is followed by rain.
What is conventional rainfall?
Caused when the ground and lower atmosphere are heated by the suns energy causing rising thermals of air; humidity in the air condenses when it cools at a higher altitude, forming towering cumulo nimbus clouds which is often followed by intense rainfall
What are the 7 flows (fluxes)
Interception
Infiltration
Throughflow
Run off (surface flow)
Saturated overland flow
Percolation
Groundwater flow
What is interception?
A layer of vegetation that intercepts precipitation before it reaches the ground. Trees are particularly effective during the full leaf period, with stem and drip flow to the ground. Plants also absorb water through their roots.
What is infiltration?
The movement of water downwards through spaces in the soil which continues until the soil becomes saturated.
What is throughflow?
The movement of water downslope through the soil towards a base level (river, lake or sea)
What’s surface runoff?
When rain falls onto the ground it may flow over the surface whne it is so intense that there is no time for it to infiltrate.
What’s saturated overland flow?
If soil spaces are full of water then any further rain cannot infiltrate and so will run off the surface.
What is percolation?
The movement of water downwards through porous or permeable rocks
What is groundwater flow?
The downwards and sideways movement of water in rock layers under the influence of gravity and rock structure
What are the 3 outputs in the hydrological cycle?
Evaporations
Transpiration
Channel flow
What is evaporation?
The change in state of water form liquid to gas when heated by the sun; this happens from oceans, lakes, rivers, top soil and plant surfaces. It increases with temperature, wind and dark surfaces.
What is transpiration and evapotranspiration?
Plants absorb water from the soil through their roots, to use within the process of photosynthesis; they then transpire (move) moisture to the surface of their leaves where it is evaporated from. This increases with tree cover, leaf growth and soil moisture.
What is channel flow?
Run off moves to the lowest points in a landscape where it collects to form a linear body of water flowing over the ground (eg a river). The larger the amount of water, the larger the discharge. It increases with amounts of water or snowmelt.
How does climate influence the hydrological cycle?
Amount of precipitation and seasonal patterns
More runoff when precipitation is more intense
Evaporation or transpiration is greater when hotter
How does vegetation influence the hydrological cycle?
Type, amount of land cover
High transpiration rates increase local rainfall
Large forests intercept a lot of rain, slowing infiltration, runoff and throughflow
Extensive tree cover will increase evapotranspiration and reduce channel flow
How does soil influence the hydrological cycle?
Depth and structure
Soils with more spaces allow more water to infiltrate, reducing overland flow but increasing throughflow
Clay soils reduce infiltration and so increase evaporation from the ground and run off
How does geology influence the hydrological cycle?
Permeability, porosity
Permeable or porous rocks allow more percolation and so increase groundwater flow
Impermeable rocks prevent percolation, perhaps causing soils to become more saturated and leading to more overland flow
How does relief influence the hydrological cycle?
Slope angle, altitude, shape
Orographic rainfall created by high ground
Steeper slopes cause reduced infiltration, more run off and faster throughflow
Slopes direct water into channels
What Human disruptions can disrupt the hydrological cycle?
Deforestation
Land use change
Reservoir creation
Abstracting water
Why does deforestation affect the hydrological cycle?
Removal of tree cover reduces interception and evapotranspiration, increasing run off, soil erosion and flooding during intense rainfall events. Reduced evapotranspiration may cause local droughts as rainfall reduces
Why does land use change affect the hydrological cycle?
Changing catchment areas from natural vegetation to urbanised impermeable surfaces increase run off and channel flow creating higher discharges and more flooding
Why does reservoir creation affect the hydrological cycle?
Damming a faucet prevents channel flow, reducing discharge downstream and creating an evaporation source
Why does abstracting water affect the hydrological cycle?
People use water for several reasons and sometimes this is taken from sources faster than it can be replaced
What is a water budget?
The balance between inputs and outputs, which are influenced by climate. This determines the among of moisture in soils.
What is the water budget equation and how does it work?
Allows a calculation of water supply during a year and identification of time periods when there may not be enough to meet natural and human needs
Precipitation = channel discharge + evapotranspiration +/- change in storage
Why are water budgets becoming a concern?
Climate change may be altering them around the world with different annual precipitation patterns, higher evt rates and more droughts and severe flooding
Why is soil moisture important?
For successful plant growth
- in an ecosystem it is important to have enough soil moisture so that plants support other trophic levels (feeding groups)
- for farmers it is important to have enough soil moisture to produce high yields of crops
> high soil moisture is necessary during spring and summer as this is growth season
Why do humans need water?
Farming, industry, life, cooling machinery and HEP
What does the water budget determine?
How much water is availible because some regions or areas have more precipitation than others
Why might some regions or areas have more precipitation than others?
Mountains or inter tropical convergence zones
Rivers, lakes and groundwater
Why might an area experience water stress despite having sources of water?
Some of the sources like rivers and lakes are constantly replenished but others, like fossil water are not
Why might the water budget experience changes in an area?
Due to global warming
What is orographic rainfall?
Relief rainfall
Cause when humid air is forced to rise over mountains. When the air cools at a higher altitude, moisture condenses and falls due to gravity. Most rain falls on the slopes facing the wind direction and tops of the mountains, with drier air on the other side so less rain falls (rain shadow)
What’s frontal rainfall?
Caused when warm humid air is forced to rise at a warm or cold front, usually as part of a low pressure system (depression). Again, the air cools, condenses and clouds of water droplets form which is followed by rain
What is conventional rainfall?
Caused when I he ground and lower atmosphere are heated by the suns energy causing warm air to rise
Humidity in the air condenses as it cools at a higher altitude and forms cumulo nimbus clouds which are often followed by heavy rainfall or thunderstorms
What are the 7 flows or fluxes?
Interception
Infiltration
Throughflow
Direct run off
Saturated overland flow
Percolation
Groundwater flow
What’s interception?
Precipitation being intercepted by vegetation before it reaches the ground. Trees are particularly effective at this when they have all their leaves, with stem and drip flow to the ground. Plants also absorb water through their roots
What is infiltration?
The movement of water downwards through spaces in the soil which continues until capacity is reached and the soil becomes saturated
What’s through flow?
The movement of water downslope through the soil towards a base level (river, lake or sea)
What’s surface run off?
Rain falling onto the ground that flows over the surface when it’s so intense there’s no time for it to infiltrate
What’s saturated overland flow?
If all soil spaces are full of water then any further rain cannot infiltrate so will run off the surface
What’s percolation?
The movement of water through porous or permeable rocks
What’s groundwater flow?
The downwards and sideways movement of water in rocks layers under the influence of gravity and rock structure
What are the 3 outputs?
Evaporation, transpiration and channel flow
What’s evaporation?
The change in state of water from liquid to gas when heated by the suns energy causing
This happens from lakes, rivers, top soil and plant surface.
It increases with temperature wind and dark surfaces
What’s channel flow?
Run off moving to the lowest point in the ground where it collects to form a linear body of water flowing over the ground (like a river or stream). The larger the amount of water, the larger the discharge
It increases with the amount of rainfall or snow melt.
What’s transportation?
Plants absorb water from the soil through their roots, to use within the process of photosynthesis; they then transpire moisture to the surface of their leaves from where it is evaporated (evapotranspiration). It increases with tree cover, leaf growth and soil moisture.
What’s evapotranspiration?
Plants absorbing water from the soil through their roots to use in photosynthesis, then transpiring it to the surface of their leaves from which it is evaporated.
What does land use change affect?
The movement of water after precipitation, such as interception and absorption by forests or the impermeable surfaces of urbanisation.
How can land use zoning reduce flood risk?
By controlling building on floodplains
What are the factors that affect river regimes?
Seasonal precipitation patterns
Seasonal temperature patterns
Main geology and soil type
Human alterations to profile
Discharge
What are seasonal precipitation patterns and why do they affect river regimes?
Some areas are wet or dry all year and there is little variation.
However other climates have wet and dry seasons and there is a big difference in discharge.
What are seasonal temperature patterns and why do they affect river regimes?
Tropical areas have a similar temperature all year so EVT rates are similar
Some areas have warm and cold seasons so there is a much larger difference
Frozen ground can also affect run off
What is geology and soil type and why do they affect river regimes?
Some areas are dominated by impermeable rocks and or soils which increase run off creating variations in the regime. Those with porous soils and rock have a more constant flow.
What are human alterations and why do they affect river regimes?
Building of dams etc as they create a more regular discharge downstream
What is discharge and why does it affect river regimes?
The amount of water passing through in cubic metres per second
What factors affect storm hydro graphs?
Drainage basin size and shape
Drainage density
Soil and rock types
Local relief of land
Vegetation cover
Precipitation intensity and duration
Human land uses and channel alterations
Why does drainage basin size and shape affect storm hydro graphs?
Smaller and more rounded catchment areas create a fast response and flashy hydrograph
Why does drainage density affect storm hydro graphs?
More tributaries collect rain quickly and creating a fast response in the main river
Why does soil and rock types affect storm hydrographs?
Impermeable types cause more run off and a rapid increase in discharge
Why does local relief of land affect storm hydro graphs?
Steep valley slopes increase fun off and speed through flow, shortening lag time
Why does vegetation cover affect storm hydro graphs?
Lack of natural vegetation cover, especially forests, decreases interception and absorption and shortens lag time
Why does precipitation intensity and duration affect storm hydro graphs?
High intensity or prolonged rainfall causes more water to get to the main river more quickly
Why does human land uses and channel alterations affect storm hydro graphs?
Urban developments increase impermeable surfaces, which increase run off; concreting and channel straightening also increase discharge
Draw a hydrograph
What is drought and how much of earths land area and population does it affect?
A slow onset hazard affecting 10% of earths land area and 18% of the population
Why is drought a matter of perspective?
In the middle of a desert you would not expect much precipitation so even though it’s dry you wouldn’t be concerned
Why may some areas have less water availible?
Weather conditions may remain dry for a longer period than normal
Farmers may experience a fall in soil moisture levels
Water levels in rivers and reservoirs fall
Human demand for water is greater than supply
What are short term causes of drought?
Blocking anti cyclones
Reduced soil mositure
Why are blocking anticyclones a short term cause of drought?
In mid latitude areas the polar front jet stream may move northwards allowing subtropical high pressure areas to also move northward. This brings stable, calm and hot weather to an area with little rainfall like the uk in summer 2018
Why is reduced soil moisture a short term cause of drought?
There may not be enough precipitation to soak into soils because plants use it quickly during the growing season or there is high evaporation because of drier air
What are some medium term causes of drought?
El Niño southern oscillation
Hydrological reasons
Why is the El Niño southern oscillation a medium term cause of drought?
ENSO cycles occur in the Pacific Ocean on average every 7 years. During El Niño warm water moves closer to the americas which reduces rainfall in the western pacific. During La Niña warm water moves to the extreme west of the tropical pacific reducing rainfall in western parts of the americas. These cycles are now known to have global effects, such as La Niña events causing drought in east Africa
Why can the hydrological cycle be a medium term cause of drought?
Reduced amounts of water in rivers or the ground may occur if precipitation is reduced in mountainous areas over several years which reduces the amount of snowmelt
What are some long term causes of drought?
Global atmospheric circulation
Climate change
Why is global atmospheric circulation a long term cause of drought?
Descending air between the Hadley and Ferrel cells and between polar cells creates hot and cold deserts respectively. Areas adjacent to these are influenced creating semi arid climates where droughts are common.
Why is climate change a long term cause of drought?
Higher temperatures are changing atmospheric systems. Subtropical high pressure areas are getting stronger which stops the seasonal movement of intertropical convergence zones. Rainfall events have become more intensive rather than being spread out over time. High sea temperatures have also changed evaporation and wind patterns which may cause rain bearing winds to fail and have changed ocean currents where cold currents become stronger evaporation is reduced and drier conditions result
What human activities contribute to drought risk?
Over abstraction of surface and ground water
Deforestation
Climate change
Why does over abstraction of surface water affect drought risk?
Taking too much water out of streams, lakes and rivers reduces the amount of water stored or transferred to areas downstream. If precipitation inputs are not enough to replenish these stores and flows then drought can be made worse
Why does over abstraction of ground water affect drought risk?
Taking too much water out of aquifer stores lowers the water table and makes wells dry up, reducing availability. If precipitation inputs are lower than the water taken out, then drought conditions get worse.
Why does deforestation affect drought risk?
Reduces interception, absorption and evapotranspiration so that water is lost from local areas making them drier and more susceptible to drought
Why does climate change affect drought risk?
Emissions of greenhouse gases are accelerating global warming which is changing precipitation patterns, making some areas more likely to experience drought
Why are wetlands particularly vulnerable to drought?
Wetland eco systems have adapted to the presence of water so if conditions become drier the entire ecosystem is very vulnerable
If inputs of water are reduced then areas of open water shrink or dry up then soil moisture is lower and dry soils can be eroded and the capacity to absorb floodwaters or provide water sources during a drought is reduced
What processes occur in wetlands that can be altered by drought?
The oxidation of soil which releases carbon into the atmosphere and nutrients or pollutants may become dangerously concentrated
Why can biodiversity be reduced by droughts in wetlands?
Some species will leave the area like aquatic birds. Others that have lost their habitat may die and plants that are unable to adapt may be lost
Why are forests particularly vulnerable to drought?
They have an important role in the water and carbon cycle
They require a lot of water due to their large size, especially fast growing species like pine
Drought causes growth to slow and creates stress which may cause them to lose leaves meaning they can’t photosynthesis as much so they die
It can take between 2 and 4 years for a tree to recover
What does drought weakening trees make them more vulnerable to?
Being attacked by pests like pine bark beetles and diseases as they can survive warmer and dryer winters that result from global warming
What can trees dying off affect?
Habitats and food chains
When is flooding a possibility?
Anywhere that experiences meteorological conditions that cause a lot of precipitation. It can be fast onset in the form of flash floods or slower onset
What is the most common cause of flooding?
When a river reaches and then exceeds bank full discharge; additional water cannot be contained within the channel so it spills over onto the surrounding land (floodplain)
This can affect anything on the floodplain including humans
What are some meteorological causes of flooding?
Intense storms
Heavy rainfall
Monsoon rains
Prolonged rainfall
Snowmelt
Why are intense storms a cause of flooding?
Severe storms such as tropical cyclones bring a lot of rainfall in a relatively short period
This water cannot move quickly into channels as it is unable to all soak into the ground causing them to overflow their banks
In arid areas occasionally a lot of rain suddenly runs over baked dry ground and causes flash floods
Why is heavy rainfall a cause of flooding?
A lot of rainfall may fall over a short period perhaps caused by a cold front in a low pressure system. This is too much to allow throughflow or groundwater flow to take place, so the excess water quickly runs off the surface and into river channels where discharge increases to flood levels
Why are monsoon rains a cause of flooding?
Subtropical areas have a wet season; these are especially wet where land areas are found between mountains and a warm ocean
Monsoon seasons are characterised by torrential rainfall which initially falls onto dry hard ground, increasing run off and then onto saturated ground, with the months of heavy rain adding to runoff and increasing river levels until they flood
Why is prolonged rainfall a cause of flooding?
Persistent rain over a long period of time, perhaps the result of several low pressure systems passing over an area causes a sequence of frontal rainfall. First the soil is saturated so that later rainfall however small cannot infiltrate. Runoff is increased and quickly enters river channels and causes floods.
Why is snowmelt a cause of flooding?
In some areas like mountains, winter snowfall can accumulate to a significant depth. Wagner temperatures in spring cause the snow to start melting often quite rapidly the ground under the snow may still be frozen so a lot of the meltwater flows rapidly down steep slopes into river valleys causing increased river discharge.
What human actions perpetuate flood risk?
Land use chnage
Hard engineering
Floodplain use
Why is land use change a human cause of flood risk?
Removal of natural vegetation especially detestation chnaged hydrological processes in the catchment area. Farmland and impermeable surfaces like roofs increase run off as interception and absorption are reduced. Hydrographs are flashy and soil erosion is increased adding sediment to river channels. This changes their shape and reduces capacity so that they flood with a lower discharge
Why is hard engineering change a human cause of flood risk?
Bridges narrow channels and reduce capacity which causes higher water levels upstream or suddenly downstream if the bridge collapses. Artificial levees increase channel capacity but transfer more water downstream increasing flood risk; if they break, flooding happens quickly over a wide area. Channel straightening transfers more water quickly downstream which increases risk.
Why is flood plain use a human cause of flood risk?
Population pressures and rural to urban migration increase building on floodplains. Deposits flood protection measures, major floods can still occur which causes a huge risk. Floodplains may be drained for farming or construction but the land shrinks as it dries out taking it below even normal river levels.
What are some environmental impacts of flooding?
Ecosystems can benefit in the short term from having water levels replenished which helps to replace nutrients. However, extreme floods cause soil and river channel erosion; then a loss of sediment, orgasmic particles and pollutants get into rivers and lakes which damages aquatic and floodplain ecosystems. Plant biomass, invertebrates and fish in rivers are reduced.
Soils may become waterlogged on level ground or scouted away on slopes but in teased surface flow. Flood events reduce the microbial biomass in soil but in the long term more nutrient rich sediments especially on floodplains are provided.
What processes are changing due to climate change?
Precipitation and evaporation, flows, and stores
How is climate change affecting different parts of the world differently?
Northern hemisphere tundra and boreal areas will be wetter as will India, most parts of Indonesia and east Africa. However, much of the rest of the world will be drier especially where there are Mediterranean climates. Over 70% of the world will experience more run off with flooding more frequent in tropical and subtropical areas due to increased evaporation and increased precipitation.
What stores are likely to be affected by climate change?
Snow pack
Glacier mass
Lakes and reservoirs
Permafrost
Soil moisture
What flows are likely to be affected by climate change?
Evaporation
Precipitation
Run off and stream flow
How will snow pack be affected by climate change?
The amount of snow collecting and surviving from one winter to another is decreasing as air temps increase. Snow depths are decreasing and early melting is becoming more common
How will glacier mass be affected by climate change?
Most glaciers around the world are in retreat, shrinking towards their ice cap sources, due to warmer temperatures causing ablation (melting), especially in lower altitudes. Even glaciers in Antarctica are thinning as ice shelves on the warmer sea melt and break up, allowing the glaciers to move faster
How will lakes and reservoirs be affected by climate change?
Higher evaporation rates from open water surfaces due to warmer air temperatures have decreased water heights and lower precipitation means they are not refilled
How will permafrost be affected by climate change?
Tundra areas are experiencing the greatest degree of warming; therefore all forms of permafrost are experiencing melting. This is changing the surface and soils of these areas.
How will soil moisture be affected by climate change?
Some levels have increased, others have decreased depending on the place.
Higher temperatures have drawn more water from the soils via evaporation
How will evaporation be affected by climate change?
This has increased a lot over oceans and land. This has increased the amount of water in the atmosphere
How will precipitation be affected by climate change?
Higher humidity in the atmosphere creates a greater potential for condensation and precipitation but patterns will be variable. Often rainfall is likely to be heavier and more intense.
How will run off and streamflow be affected by climate change?
Where precipitation is in heavy, short bursts or prolonged, due to higher humidity levels or where snow and ice are melting more water will run off the surface and enter streams which increases flood risk
Why are some regions affected by climate changes every decade or so?
Due to changes in atmospheric circulation that also affect warm and cold ocean currents.
This relates to ENSO which creates uncertainty in water supplies for Oceania, south east Asia, the Pacifics and the Americas.
What areas experience water insecurity during La Niña and water security during El Niño?
East Africa
Afghanistan
Pacific islands
Southern USA
Ecuadorean
Uruguay
Chile
Sri Lanka
What areas experience water insecurity during El Niño and water security during La Niña?
Sahel
Southern Africa
Northern India
Indonesia
Australia
Northern Brazil
North east USA
What processes take place in wetlands that can be affected by drought?
Oxidation of soils which releases carbon into the atmosphere and nutrients or pollutants can become dangerously concentrated
Why may species be affected by wetlands drying out?
Some species like certain types of aquatic birds may leave the area. Others that have lost their habitat may die and plants that are unable to adapt will be lost
Why are forests particularly vulnerable to drought? What negative affects can there be if they dry out?
Forests have an important role in the water and carbon cycle
Due to their size, trees require a lot of water especially fast growing species like pine. Drought slows growth and causes stress
Trees may lose their leaves and be unable to photosynthesis, so they die. It can take between 2 and 4 years for a tree to recover from a drought.
Droughts also make trees vulnerable to being attacked by pests (pine bark beetles) and diseases as dry warm winters allow them to survive
What is affected by trees dying off due to drought?
Habitats and alters food chains
What are trees vulnerable to during droughts?
Pine bark beetles and diseases as they can both survive dry warm winters during which they’re usually killed off
When is flooding possible?
In any place experiencing meteorological conditions providing a lot of precipitation, flooding is always possible
It can be fast onset like a flash flood or slow onset
What is the most common cause of flooding?
When a river reaches and then exceeds bank full discharge
Additional water cannot be contained within the channel and so spills over onto the surrounding land (floodplain)
Anything living on this floodplain, including humans, will be affected
What 5 factors cause flooding?
Intense storms
Heavy rainfall
Monsoon rains
Prolonged rainfall
Snowmelt
Why are intense storms a meteorological cause of flooding?
Severe storms like tropical cyclones bring a lot of rainfall in a relatively short time period. This water moves quickly into river channels as the ground it too saturated meaning it can’t soak in causing them to overflow their banks. In arid and semi arid areas, occasional thunderstorms drop a lot of rainfall suddenly which runs quickly over baked ground causing flash floods
Why is heavy rainfall a meteorological cause of flooding?
A lot of rain may fall over a short period perhaps caused by a cold front in a low pressure system. This is too much to allow throughflow or groundwater flow to take place, so the excess water quickly runs off the surface and into river channels where discharge increases to flood levels
Why is snowmelt a meteorological cause of flooding?
In some areas like mountains, winter snowfall accumulates to considerable depth. Warmer temperatures in spring cause the snow to start melting often quite rapidly. The ground under the snow may still be frozen so a lot of the meltwater flows rapidly down steep slopes into river valleys causing increased discharge.
Why is prolonged rainfall a meteorological cause of flooding?
Persistent rain over a long period of time, perhaps the result of several low pressure systems passing over an area caused a sequence of frontal rainfall. First the soil is saturated so that later rainfall, however small, cannot infiltrate. Run off is therefore increased and quickly enters river channels which causes floods
Why are monsoon rains a meteorological cause of flooding?
Subtropical areas have a wet season; these are especially wet where land areas are found between mountains and a warm ocean (like in India). Monsoon seasons are characterised by torrential rainfall which initially falls onto dry hard ground - increasing run off - with the months of heavy rainfall which increase river levels causing floods
What human actions affect flood risk?
Land use change
Flood plain use
Hard engineering
Why is land use change a human cause of flooding?
Removal of plants especially in the form of deforestation can change hydrological processes in the catchment area. Farmland and impermeable surfaces such as roofs increase run off as interception and absorption are reduced. This creates flashy hydrographs. Soil erosion is also increased which adds more sediment to river channels meaning they have lower capacity and flood more easily
Why is floodplain use a human cause of flooding?
Population pressures and rural to urban migration increase building on floodplains. Despite flood protection measures, major floods can still occur, causing huge risk. Floodplains may still be drained for farming or construction but the land shrinks as it dries out, taking it below even normal river levels
Why is hard engineering a human cause of flooding?
Bridges can contribute to narrowing river channels which can reduce capacity and cause higher water levels upstream or suddenly downstream if a bridge collapses. Artificial levees increase channel capacity but transfer more water downstream and if they break can cause quick widespread floods.
Channelisation (straight concrete channels) transfers more water quickly downstream also increasing risk
What are two environmental impacts of flooding?
Ecosystems
Soils
Why are ecosystems impacted by flooding?
Small floods can be beneficial as they replenish water levels and create wetlands
Larger floods however can increase soil and river erosion and can allow pollutants to get into water systems which damages aquatic and floodplain ecosystems. This can reduce plant biomass, invertebrates and fish in rivers
Why are soils impacted by flooding?
Soils may become waterlogged on ground level or eroded away on slopes by increased surface flow. Floods also reduce the microbial biomass in soils but in the long term can provide more nutrient rich sediment
What is the most reliable source for data on climate change?
The IPCC which is the intergovernmental panel on climate change
This data is produced by scientists from around the world undergoes peer review
What are some general effects of climate change?
The northern hemispheres tundra areas are likely to be wetter as will India and parts of east Africa
However, much of the rest of the world will be drier like the Mediterranean
Over 70% of the land area will experience more run off with flooding more frequent in tropical and subtropical areas due to increased evaporation and intense precipitation
What stores will be affected by climate change?
Snow pack
Glacier mass
Lakes and reservoirs
Permafrost
Soil moisture
Why will snow pack be affected by climate change?
The amount of snow collecting and surviving from one winter to another is decreasing as air temperatures rise. Snow depths have also been decreasing and early melting has been observed
How is glacier mass affected by climate change?
Most glaciers around the world are in retreat and shrinking towards their ice cap sources due to warmer temperatures especially at lower altitudes
Even glaciers in Antarctica are thinning as ice shelves on the warmer sea melt and break up allowing the glaciers to move faster
What is ablation?
Melting
How can lakes and reservoirs as a store be affected by climate change?
Higher evaporation rates from open water surfaces due to warmer temperate have decreased water levels and lower precipitation means that they are not refilled in times of drought
How is permafrost as a store affected by climate change?
Tundra areas are experiencing the greatest degree of warning and this means all forms are melting
This is changing the surface and soils of these areas
How is soil moisture as a store being affected by climate change?
A great contrast around the world as in some places soil moisture levels have increased and others have decreased. But higher air temperatures mean that more water has been drawn from soils by evaporation
How is evaporation as a flow being impacted by climate change?
This has increased a lot especially over the oceans but also over land. This has increased the amount of moisture in the atmosphere.
How is precipitation as a flow being affected by climate change?
Higher humidity in the atmosphere creates a greater potential for condensation and precipitation but patterns will be variable. Often rainfall is likely to be heavier and more intense.
Why is run off and stream flow as a flow being affected by climate change?
Where precipitation is in heavy, short bursts or prolonged due to higher humidity levels, or where snow and ice are melting more water will run off the surface and enter streams, increasing flood risk
Where experiences water insecurity during La Niña and water security during El Niño?
East Africa (nov-Mar)
Afghanistan (jan-May)
Pacific islands (jun-apr)
Southern USA (oct-apr)
To name a few places
What places experience water insecurity during El Niño and water security during La Niña?
Sahel (jul-sep)
Southern Africa (nov-mar)
Northern India (jun-sep)
Indonesia (jun-jan)
Why is there concern surrounding water supplies now and in the future?
Climate change is causing patterns of weather to change which is creating insecurity in some areas
How does climate change affect some regions differently over time due to the global atmospheric circulation system?
Some areas are affected every decade or less due to atmospheric circulation that also affects warm and cold ocean currents.
ENSO cycles
How has long term climate change affected water security?
Global warming has increased the variability of precipitation with periods of unusually low rainfall and then periods of very intense rainfall
Some regions are becoming drier and others wetter
There is increasing uncertainty over water levels in rivers and the ground as there may be more fun off and less water going into sources such as the ground
Also there may be less contamination due to concentrations of naturally occurring and human inputs of chemicals like salts
Higher temperatures have also increased evaporation and transpiration which reduces effective precipitation and makes it difficult to store water
What are some water security concerns?
Although the world’s population increase is slowing down there are going to be a billion more people trying to find water by the middle of the century. Thsi will be a difficult task in some areas which will become much drier
What is water supply
The amount of accessible freshwater from precipitation and surface and ground water sources
What is water demand?
The amount needed by people for consumption or activities like farming and industry
What’s water stress?
Where annual water supplies drop below 1700m3 per person
What’s water scarcity?
Where annual water supplies drop below 1000m3 per person
What’s water insecurity?
When people do not have enough water to sustain livelihoods, human wellbeing and socio economic development
What is the water supply and demand balance?
Assessing wether a place has enough water to meet their needs
What type countries tend to not have issues with supply?
Countries with big land area or small populations are usually able to balance better
However even in big countries there can be issues with the transfer of water
> China North to South water transfer
What countries have the smallest supply of water?
Arid and semi arid countries have the smallest supply
Like the Middle East
What countries have the largest supply of water?
Tropical and temperature countries
Like Brazil and Ireland
What kind of countries have the hardest time finding a balance?
Countries with large or dense or very urbanised populations
India, Bangladesh and the Netherlands
Why is the demand for water increasing?
Living standards are increasing which requires more water and as populations have grown so has the demand for water for domestic, farming and industrial uses
What are the 4 issues that are placing pressures on finite freshwater resources?
Increased population
Economic development
Better living standards
Farming
What does finite mean?
a natural resource that cannot be readily replaced by natural means at a pace quick enough to keep up with consumption.
Why is increasing population placing pressure on freshwater resources?
Global population continues to increase but at a slower age
Wafer is an essential resource for everyone
The UN estimates that there will be a 55% increase in demand between 2015-2055
Why is economic development placing pressure on freshwater resources?
World increased by an average of 3.5% per year from 1960 to 2012 more water used by industries, businesses and energy use
Why is farming placing pressure on freshwater resources?
Uses the most water (70% globally)
As demand for food increases so does the use of water for irrigation and livestock farming
Why are better living standards placing pressure on freshwater resources?
As more countries have emerged economically, their populations have gained more wealth so they consume more water directly (eg for washing machines) and indirectly (food choices, house building and energy use etc)
What are some physical causes of water insecurity and why do they happen?
Climate variability:
The earths different hot, cold, wet and dry climates all have water budgets which are being chnaged by climate change
Precipitation may decrease or warmer water may house harmful bacteria
Salt water encroachment:
In some coastal areas seawater is able to intrude into groundwater and up rivers which contaminates these water sources with salt. This is becoming more common as sea levels rise
> Kiribati
What are some human causes of water insecurity and why do they happen?
Over abstraction from surface and ground water:
The demand for water and lack of controls has led to more water being taken. This reduces local supplies and meat costs allows greater salt water intrusion
Contamination by farming and industry:
Chemicals and other wastes may enter water sources which causes pollution and an increase in organisms that are harmful to human health
Climate change:
Enhanced warming has accelerated sea level rise and salt encroachment and reduced water quality with bacterial growth in warmer waters
What is physical water scarcity?
The lack of available clean water sources (ie semi arid climates)
Water is also scarce in any climate area where over 75% of supply is withdrawn for human usage
What is economic water scarcity?
Access to water resources being limited by:
Poor management of supply and use
Lack of financial ability to develop them
Affordability
Why is water needed for human wellbeing?
Health (clean drinking water, free of disease)
Cleanliness (improved social dignity)
Food (watering crops and animals provides more food to eat avoiding malnutrition)
Ecosystems (maintain environmental health so services and resources available)
Human rights (disadvantaged groups require safe drinking water water and sanitation)
What are 5 ways water can be used for economic development?
Energy production
Manufacturing
Economic confidence
Farming
Control pollution
How is water used in energy production linked to economic growth? How can it be problematic?
Directly in HEP, indirectly to produce steam
Can cause port cuts and shortages if water supplies are too low
How is water used in manufacting linked to economic growth? How can it be problematic?
Directly in production, indirectly to cool machines
Cant increase production if shortages of water
How is water used in economic confidence linked to economic growth? How can it be problematic?
Water resource availability aids investment in businesses
Unsustainable economy; water costs create conflict
How is water used in farming linked to economic growth? How can it be problematic?
Irrigation water to increase yields
Cant increase production if shortages
How is water used in control pollution linked to economic growth? How can it be problematic?
Contaminated water
Cannot be used if not clean
What is the role of the environment in controlling the amount of water?
Freshwater ecosystems control flooding and store clean water provide fisheries and recreation
Forest ecosystem services control flows in the hydrological cycle enable recharging of groundwater and filter water to clean it
Degraded ecosystems are less productive and have disrupted food webs and higher concentrations of salts and contaminants
Why is the cost of water important when considering scarcity?
Cost of supplying water varies largely across the world and this is only rising
Supplying clean water needs construction of infrastructure to abstract, clean and move it
Waste water also needs to be collected and treated after use to remove harmful bacteria before returning it to the natural environment
Developed countries are more able to provide expensive infrastructure and people can afford water rates
> developing countries with unchecked urbanisation and widespread poverty have difficulty
Why are there conflicts over water?
Freshwater is an essential resource which in some countries and regions is shared because a lake, river or groundwater crosses political boundaries
> the Colorado river
Environmental concerns have arisen due to water shortages
> shrinking of the Aral Sea
International tensions arise when major rivers flow through several countries or large aquifers extend under international boundaries
The UN estimates that 40% of the world relies on trans boundary water supplies (2bn of which is groundwater)
> half of these situations don’t have a formal agreement
What are some sustainable schemes to manage water and how do they work?
Restoring water supplies:
Restoring or enhancing the natural hydrological cycle in a local area by recovering rivers with their flood plains, water harvesting or creating green spaces and permeable surfaces
Water conservation:
Smart irrigation involves giving crops just under the right amount of water that they normally need during growing or using efficient methods like drip irrigation
Water recycling:
Involves collecting used (grey) water and using it for non drinking purposes like washing or preparing food and flushing toilets
What are some hard engineering schemes for manage water and how do they work?
Water transfer:
Moving water from one drainage basin to another by diverting rivers or using pipelines. This directs water to where it is needed but needs expensive infrastructure
Mega dams:
Large dams across a river where there are deep gorges or valleys that trap water in a large reservoir
> a new water store is created for local and regional use but natural river flows are altered
Desalinisation:
Taking sea water and separating it from the salts
> the oceans are the worlds main sources of water so will not run out but it requires a lot of energy and is expensive
> the salt left over can also be problematic
What is integrated water management?
Drainage basins may be large and involve many human activities and hydrological processes
To manage all of these efficiently and in a sustainable way, all administrators and stakeholders must agree and coordinate policies and actions
This is not easy to achieve especially when several countries, often with opposing views are involved
Geographers and scientists are responsible for collecting and providing information to inform this management process
What are treaties and frameworks that manage water?
The UN convention on the law of the non-navigational uses of international watercourses (2014) produced roles for equitable and reasonable use of water without harming neighbouring countries
The Nile river basin framework (1999 between 10 countries) need effective monitoring, enforcement and conflict resolution as well as water allocations matching flow variations to meet changing needs
The Berlin water framework directive and hydropower is a European initiative consisting of nine water management principles enshrined into international law. This includes:
- management maximising availability and reliability of water supplies
- river basins managed in an integrated way
- long term planning of needs
- minimising environmental damage
- cooperation of countries or regions
- everyone receiving their fair share
These rules are difficult to implement and enforce especially on trans boundary situations: since the 1960s, 150 treaties have been signed but there have been 37 violent disputes
