A Level Edexcel Water Cycle Enquiry Question 2

[5.4A] What is drought?

A deficiency of water over an extended time period, usually at least a season.

[5.4A] What are the types of drought?

Socio-economic/famine, hydrological, agricultural and meteorological.

[5.4A] What is meteorological drought?

The shortfalls in precipitation as a result of short-term variability (natural variations in atmospheric conditions) or longer-term trends which increase the variations of the dry period. (longer term such as occurrence of El Nino events and climate change.) This is basically a rainfall deficit.

Features:

- Low precipitation.

- High temperatures.

- Strong winds.

Impacts:

- Loss of soil moisture.

- Supply of irrigation water declines.

[5.4A] What is hydrological drought?

Hydrological drought is associated with reduced stream flow, and groundwater levels which decrease because of reduced inputs of precipitation and continued high rates of evaporation.

Features:

- Reduced infiltration.

- Low soil moisture.

Impacts:

- Reduced storage in lakes and reservoirs.

- Less water for urban supply.

- Poorer water quality.

[5.4A] What is agricultural drought?

The rainfall deficiency from meteorological drought leads to deficiency of soil moisture and soil water availability, which has a knock-on effect on plant growth and reduces biomass. This can be accelerated by agricultural practices, such as overgrazing. This is basically a soil moisture deficit.

Features:

- Low evapotranspiration.

- Plant water stress.

Impacts:

- Poor yields from raid-fed crops.

- Irrigation systems start to fail.

[5.4A] What is socio-economic/famine drought?

This is a humanitarian crisis which the widespread failure of agricultural system leads to food shortages, potentially causing famine and starvation.

Features:

- Loss of natural vegetation.

- Increased risk of wild fires.

- Wind-blown soil erosion.

Impacts:

- Widespread failure of agricultural systems.

- Food shortages on a seasonal scale.

- Rural economy collapses.

[5.4A] How does the El Niño cycle cause drought?

ENSO cycles occur in the pacific ocean on average every 7 years. El Niño moves warm water 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.

- It is thought that temperature anomalies provide the key to ENSO, which, in turn is thought to trigger the occurrence of drought. El Nino always leads to relatively weak monsoon rains, exacerbating drought.

[5.4A] What are the normal conditions in the pacific basin (ENSO)?

- Trade winds from the East (Peru) move to the West (Australia, and parts of Asia .)

- The wind pushes the warm water westwards, causing water to pile up.

- As the warmer water gets pushed away from the west, it's replaced by cold water which is pulled up from deeper down the ocean. This is called upwelling.

- Warmer water adds extra heat to air, which causes the air to rise. This air condenses to cause clouds, and eventually rainfall in the West.

- Cooler drier air descends on the other side of the ocean.

[5.4A] What are the conditions for an El Nino year (ENSO)?

- The trade winds weaken or even reverse in the western pacific due to being interrupted.

- Piled up warm water in the west moves back to the East (such as Peru).

- Less upwelling of cold water on the eastern side, allowing the colder side of the ocean to warm.

- This changes rainfall patterns, causing rainfall over South America, and causes drier periods in Australia.

- Due to the warm air moving, this causes upper air disturbances which distort the path of jet streams, leading to teleconnections.

[5.4A] What are the conditions for a La Nina year (ENSO)?

This is an exaggerated version of a normal year.

- Stronger trade winds, with ocean currents and upwelling being stronger.

- The trade winds push warm water to west pacific.

- The upwelling of water is increased in south and Central America in the East.

- Sea surface temperatures in the east drop beyond normal.

- Areas such as Australia are wetter than normal.

- South America such as Peru sees more drought, due to less rainfall and high pressure.

- North America can see rainfall.

[5.4A] What are long-term causes of drought?

Climate Change

- Evidence suggests that higher temperatures are changing atmospheric system.

- Rainfall events have become more intensive rather than being spread over time.

- Higher sea temperatures have changed evaporation and wind patterns, which may cause rainfall to fall.

- It can also result in colder currents, causing evaporation to be reduced, and driver conditions as a result.

[5.4B] How does human activity influence drought risk?

Human factors do not cause drought, but they act like a positive feedback look in exacerbating its risk.

- Over-abstraction of surface water, and groundwater.

- Deforestation.

- Climate change.

[5.4B] How does over-abstraction of surface water and groundwater enhance the risk of drought?

Over-abstraction of surface water:

- This involves taking too much water out of streams, lakes, and rivers, which reduces the amount of water stored or transferred to other areas. If precipitation inputs are not enough to replenish these stores, then drought can be made wore.

Over-abstraction of groundwater:

- This involves taking too much water out of aquifer stores which lowers the water tables, potentially making wells dry up and reducing availability of water.

[5.4B] How does climate change and deforestation enhance the risk of drought?

Deforestation:

- Deforestation reduces interception, absorption and evapotranspiration so that water is lost from local areas and isn't condensed into rain, making them drier and more susceptible to drought.

Climate Change:

- Emissions of greenhouse gases are accelerating global warming which is changing precipitation patterns, making some areas more likely to experience drought.

[5.4B] What is desertification?

It is the process by which once-productive land gradually changes into a desert-like landscape.

Usually caused by:

- Changing rainfall patterns, with rainfall becoming less reliable, seasonally and annually.

- Vegetation cover becomes stressed and dies, leaving soil exposed.

- Bare soil is eroded by wind.

[5.4B] What factors exacerbate drought?

Desertification increases the risk of drought occurring.

- The over cultivation, overgrazing, and trampling of land causes the soil to be more compact, making the soil less able to absorb moisture and not refill aquifers.

- Desertification can be a sign of human activity.

[5.4B] How has human activity affected Australia's drought?

Australia:

- They have a large deficiency in rainfall, with 10% of rainfall recorded for at least 3 months.

- Big Dry is an example.

Human:

- 50% of the nation's agricultural output uses the Murray-Darlin Basin.

- Adelaide in South Australia was vulnerable, with 40% of drinking supplies being extracted here.

- This has led to the over-extraction of water where no water has flowed as its mouth.

- Growing population and affluent lifestyle has caused surface and groundwater resources to be over-extracted for agricultural, industrial and urban usage.

[5.4C] How can droughts impact ecosystem, such as wetlands?

Wetlands:

- With less precipitation, there will be less interception due to plant stress causing reduced vegetation. This means there will be less infiltration and percolation causing water table levels to fall. The processes of evaporation will continue, however, transpiration rates will decrease making wetlands less functional.

- Areas of open water (such as wetlands) shrink or dry up following a reduction in water.

- Some species will leave the area, such as aquatic birds. Plants will be lost.

[5.4C] What is a wetland, and what are some functions?

A wetland is an area of marsh, fen, peatland or water.

Functions:

- They act as temporary water stores within the hydrological cycle, thus mitigating river floods downstream.

- Chemically, wetlands act like giant water filters by trapping nutrients and pollutants such as in peat, thereby purifying water.

- They have a very high biological productivity, and support a very diverse food web.

- They can recharge the aquifers.

[5.4C] What schemes have been created regarding wetland destruction?

The 1991 Ramsar Convention on wetlands has listed over 1800 wetlands of international performance.

[5.4C] What other reasons are there for wetland destruction?

- 2.5 million square kilometers have been destroyed in Europe and the USA for agriculture and urban development.

- The formation of Dams.

- Schemes have lead to wetland drainage. For instance, the Jonglei Canal project which diverted the White Nile discharge away from the Sudd Swamp.

- Artificial damage remains the largest threat.

[5.4C] How can droughts impact ecosystem, such as forests?

Forest are key for interception which reduces infiltration and overland flows, characterised by high levels of transpiration.

- Due to their large size, trees require a lot of water, especially fast-growing species such as pine.

- It is thought that drought is increasing the susceptibility of pines and firs to fungal diseases.

- Droughts are weakening trees, so they are more easily attacked by pests such as the pine bark beetle in the Rocky Mountains of Colorado.

-Trees may lose leaves and be unable to photosynthesise, so they die. It can take between 2-4 years for a tree to recover from drought conditions.

- Trees die-off due to drought and affects habitats, and alters food chains.

- Deforestation remains the biggest threat to trees.

[5.5A] What are the three types of flooding?

Groundwater flooding:

- This is flooding that occurs after the ground has become saturated from prolonged heavy rainfall.

Surface water flooding:

- Flooding that occurs when intense rainfall has insufficient time to infiltrate the soil, so flows overland.

Flash flooding:

- A flood with an exceptionally short lag time, often minutes or hours.

[5.5A] What are the meteorological causes of flooding?

Meteorological - Short-term weather events.

Intense Storms, Heavy/Prolonged Rainfall, Monsoonal, and Snowmelt.

[5.5A] How do intense storms result in flooding?

Intense Storms:

- Severe storms such as tropical cyclones bring a lot of rainfall in a relatively short time period.

- This water moves quickly into channels (that soon reach bank full discharge), as it is unable to soak into the ground, causing them to overflow.

- The short lag time leads to flash flooding.

[5.5A] How does heavy/prolonged rainfall result in flooding?

Heavy Rainfall:

- A lot of rain may fall over a short period of time. This can be too much through flow or groundwater flow, so the excess water quickly runs off the surface into the river channels where discharge increases to flood levels.

Prolonged:

- In contrary, persistent rainfall can make the soil too saturated, so more rainfall cannot infiltrate, increasing run off which enters the channels.

[5.5A] How does monsoonal rainfall result in flooding?

Monsoonal:

- Subtropical areas have a wet season. These are especially wet. They are characterised by torrential rainfall, and ground saturation occurs very quickly.

- Around 70% of the average annual rainfall occurs during 100 days.

- The low-lying planes of the large rivers in Bangladesh, Pakistan, India and china are most at risk. Around 80% of Bangladeshi people are exposed to flood risk.

[5.5A] How does snowmelt result in flooding?

- In some areas like the continental interiors of America and Asia, winter snowfall accumulates to considerable depths. The warmer temperatures in spring cause the snow to star melting rapidly. Much of the ground is still icy, which increases the rate meltwater flows down slopes, causing increased river discharges.

[5.5A] What other physical factors increase flooding?

These tend to be basin specific, but the factors are geology, soil, topography, and vegetation.

Soil:

- Deeper soil absorbs more water and results in less run-off.

Geology:

- Permeable rock allows greater infiltration and ground storage.

Topography:

- Stepper-angled slopes mean less water is absorbed and there is greater surface run-off.

Vegetation:

- Greater vegetation cover generally produces higher levels of interception, storage and evapotranspiration. This reduces run-off and increases the lag time.

[5.5A] What other factors increase flooding?

- Low-lying areas with impermeable surfaces, as in towns and cities.

- Where the ground surface is above impermeable rocks.

- Where there is volcanic activity beneath ice sheets, jokulhalps, e.g Iceland.

- Low-lying parts of flood plains. Subject to river flooding, but also to groundwater flooding.

[5.5A] How is flooding defined?

When the discharge (volume of water) is of sufficient quantity to cause a body of water to overflow its channel.

[5.5A] What were the physical causes of the South Asia Floods (2017)

- The floods are caused by the overflowing of Brahmaputra river in July 2017 - this was due to torrential rain in the foothill of the Himalayas.

- The main cause of the floods was a heavy monsoon season.

[5.5B] How does land-use change exacerbate flood risk?

Land-Use Change:

- This refers greatly to urbanisation.

- Deforestation reduces interception, meaning the ground is infiltrated even more, and eventually surface-run off occurs.

- Speeding up the drainage of water in urban areas via drains, reduces lag time.

- Land changing for farming purposes means the tractor force compacts soil, making infiltration more difficult. Grazing animals also trample the land.

- The creation of impermeable surfaces - roofs, pavements, roads, etc.

- Draining wetlands is common to make way for urban areas. These are used to store water, and reduce flood risk. Removing these areas increases risk.

- This creates very flashy hydrographs.

[5.5B] How does river mismanagement exacerbate flood risk?

River Mismanagement:

- This refers to the use of failed hard-engineering schemes.

- Channelisation can improve river discharge, and reduce flood risk, but it displaces the river downstream, therefore other locations may be affected by greater discharge.

- Artificial levees increase channel capacity, but transfer more water downstream, increasing flood risk.

[5.5B] How does building on a floodplain exacerbate flood risk?

Floodplain Building:

- Due to high population growth, it has created pressures to increase building on floodplains. These are areas at high risk of floods.

[5.5B] What were the human causes of the South Asia Floods (2017)

- As the main cause of the flood was from the overflowing of the Brahmaputra river, this was worsened with deforestation in the Himalayas (reduced interception.)

- As a result of rapid urbanisation, Mumbai has a population of over 20 million and a population density of over 30,000 people per square kilometre.

- This increase the number of impermeable surfaces as more roads are built, increasing run-off as less

water is absorbed in the ground – therefore increase the risks of flooding.

[5.5C] What are the socio-economic impacts of flooding?

This refers to impacts on infrastructure, economic activity, and settlement impacts.

Economic:

- Insurance costs.

- Businesses damaged, with repair needed.

- Consumers and deliveries unable to reach businesses and emergency costs.

Infrastructure Impacts:

- Road and railways blocked.

- Bridges damaged or washed away.

- Schools closed.

- Water and power infrastructure disrupted, which can result in water-borne diseases.

Settlements:

- Homes flooded.

- People evacuated.

- Deaths.

[5.5C] What are more social and economic impacts of flooding?

Social:

- In many LICs many people have not learnt to swim, meaning they are vulnerable to drowning and water-borne diseases.

- Interruption of water and energy supplies.

- Disturbance of everyday life, including work.

Economic:

- Property values are severely impacted in flood prone areas.

- Destruction of crops and loss of livestock, potentially leading to widespread famine. This can lead to escalating food prices, such as in the Murray-Darling Basin of Australia in 2006.

- People's livelihoods affected by the post-flooding rebuild costs, putting them out of action for at least 6 months in most cases.

[5.5C] What are the environmental impacts of flooding?

Soils:

- Soils may become waterlogged or scoured away. However, in the long-term there is more nutrient-rich soils especially on flood plains.

- Soil erosion can increase.

Ecosystems:

- Small floods can benefit by replenishing water levels, creating new wetland habitats.

- It can lead to the distribution of sediment and nutrients around the landscape.

- It can trigger breeding, migration and dispersal of many species.

- It can prompt eutrophication which is when there are too many nutrients in a body of water which causes a dense growth of plant life, starving aquatic animals of oxygen.

[5.5C] What were the socio-economic impacts of the UK summer floods in 2007, and the background?

Tewkesbury:

Prolonged heavy rainfall in three months being more than double the average rainfall (387mm compared to average of 186mm).

Socio-Economic:

- 13 lives lost, hundreds injured.

- 50,000 homes damaged.

- 850 families evacuated to caravans.

- Water treatment works shutdown, meaning that 140,000 homes had no water supply.

- Total cost to the UK economy estimated at £3.2bn.

- 9000 businesses affected.

- 180,000 insurance claims.

[5.5C] What were the environmental impacts of the UK summer floods in 2007?

Environmental:

- Groundwater stores in Tewkesbury were refilled.

- There was widespread pollution of rivers and aquifers, leading to eutrophication.

- Debris and foreign objects deposited in the environment.

- Widespread pollution of rivers.

[5.6A] What do scientists claim about the hydrological cycle?

Climate change will result in intensification, acceleration, or enhancement of the global hydrological cycle, but it will vary around the world.

[5.6A] How does climate change affect the precipitation input?

A warmer atmosphere holds more water. There will be a widespread increase in the rainfall and the intensity will increase. However, some areas receive less rain because of changes in wind patterns.

- Areas of precipitation increase the tropics and high latitudes.

- Areas of precipitation decrease lie between 10° and 30° north and south of the Equator.

- Length, frequency and intensity of heat waves have increased widely, particularly in Southern Europe and Southern Africa. This has led to an increase in drought.

- Climate change means more snow is falling as rain now.

[5.6A] How does climate change affect the evaporation and evapotranspiration input?

- Evaporation rates have increased particularly over oceans.

- Evaporation over large areas of Asia and North America appears to be increasing.

- Transpiration is linked to vegetation changes, which in turn are linked to changes in soil moisture and precipitation.

[5.6B] How is surface run off and stream flow affected by climate change?

Evidence suggests that, along with more climate extremes, there will be an increase in hydrological extremes with more low flows (droughts) and more high flows (floods).

- An accelerated cycle with more intense rainfall will increase rates of run-off and reduce infiltration. run-off will also increase in areas where snow and ice is melting, leading to a greater chance of flood.

[5.6B] How is soil moisture affected by climate change?

- Greatly contrasts around the world, and as soil moisture is related to many factors, it's difficult to say whether climate change is the one impact.

- When precipitation increases, soil moisture would increase, however, due to increased evaporation, the two effects may cancel each other out.

[5.6B] How is snow affected by climate change?

- Many studies suggest the snow-cover season has decreased in length.

- Spring melt has occurred quicker in the northern hemisphere.

[5.6B] How is permafrost affected by climate change?

The change in the physical climate at high latitudes are leading to permafrost degradation in northern areas due to the warmer air temperature. This depends the active layer.

- Releases methane, which is an example of positive feedback.

[5.6B] How is reservoirs and lakes affected by climate change?

- The greater evaporation rates from open water surface as a result of warmer temperatures have decreased water heights, and lower precipitation in many areas means they're not being replenished.

[5.6B] How is glacier ice affected by climate change?

- There is strong evidence that glaciers have retreated globally.

- This is the result of rapid temperature increase and changes in the precipitation type from snow to rain.

- This is a declining store.

[5.6C] What problems are there with forecasting changes to the hydrological cycle?

- Difficult to disentangle the possible of climate change from those of human influences such as land changes.

- Forecasting possible changes to the hydrological cycle is distinguishing between the impacts of long-term climate change and oscillations associated with El Nino events.

- Scientists cannot make confident forecasts.

[5.6C] What are the short-term factors of climate change that are leading to diminishing water supply and increased uncertainty?

- Increases in annual temperature leads to greater evaporation from surface water in summer, although spring discharge may increase.

- Greater rates of evapotranspiration, removal of moisture from forest stores.

- Impact of ENSO is leading to increasingly unreliable patterns of rainfall. This increases uncertainty.

- Decreasing rainfall in many areas as a result of global warming.

- Increased intensity and frequency of droughts as a result of global warming and oscillation is an issue for rain-fed agriculture.