The Water cycle EQ2

Question 1

What is the UN definition of a drought?

Answer 1

An extended period - a season, a year or several years of deficient rainfall relative to the statistical multiyear average for a season.

Question 2

What are the types of droughts?

Answer 2

• Meteorological
• Agricultural
• Hydrological
• Socio- economic

Question 3

What is a meteorological drought?

Answer 3

Meteorological drought is defined usually on the basis of the degree of dryness (in comparison to some “normal” or average amount) and the duration of the dry period. Definitions of meteorological drought must be considered as region specific since the atmospheric conditions that result in deficiencies of precipitation are highly variable from region to region.

Question 4

What is an agricultural drought?

Answer 4

Agricultural Drought refers to the impacts on agriculture by factors such as rainfall deficits, soil water deficits, reduced ground water, or reservoir levels needed for irrigation.

Question 5

What is a hydrological drought?

Answer 5

Hydrological drought is associated with the effects of periods of precipitation (including snowfall) shortfalls on surface or subsurface water supply (i.e., streamflow, reservoir and lake levels, groundwater). The frequency and severity of hydrological drought is often defined on a watershed or river basin scale. Although all droughts originate with a deficiency of precipitation, hydrologists are more concerned with how this deficiency plays out through the hydrologic system. Hydrological droughts are usually out of phase with or lag the occurrence of meteorological and agricultural droughts.

Question 6

What is a famine drought?

Answer 6

A humanitarian crisis in which the widespread failure of agricultural systems leads to food shortages and famines
Food deficit:
- loss of natural vegetation
- increased risk of wild fires
- wind blown soil erosion
- desertification

Question 7

What is positive feedback?

Answer 7

cyclical sequence of events that amplifies an impact.

Question 8

What is negative feedback?

Answer 8

cyclical sequence of events that dampens down or neutralises an impact.

Question 9

What are the major features of meteorological drought?

What are the major features of hydrological drought?

What are the major features of agricultural drought?

What are the major features of famine drought?

Answer 9

Deficit: Rainfall - Low precipitation, high temperatures, strong winds

Deficit: Streamflow - Low soil moisture, little percolation and groundwater recharge.

Deficit: Soil moisture - Plant water stress reduced biomass.

Deficit: Food - loss of natural vegetation, and desertification.

Question 10

List the droughts in order of severity.

Answer 10

• Meteorological
• Hydrological
• Agricultural
• Famine

Question 11

What are El Nino southern oscillation cycles (ENSO)?

What are teleconnections?

Answer 11

• The trade wind pattern is disrupted - it may slacken or even reverse and this has a knock-on effect on the ocean currents
• The air circulation loop reversed

When this happens, cool water normally found along the coast of Peru is replaced by warmer water. At the same time, the area of warmer water further west, near Australia and Indonesia, is replaced by cooler water.
El Niño events usually occur every 3-7 years, and usually last for 18 months. El Niño events seem to trigger very dry conditions throughout the world, usually in the second year. For example, the monsoon rains in India and South East Asia often fail.

The way that changes in sea temperatures in the Eastern Pacific is linked to changes in precipitation and climate generally across the rest of the globe.

Question 12

What is La nina?

Answer 12

La Niña events may sometimes, but not always, follow an El Niño event. They involve the build-up of cooler-than-usual subsurface water in the tropical part of the Pacific. This situation can lead to severe drought conditions, particularly on the western coast of South America.

• Very strong air circulation and very warm water moving east-west.

Question 13

What are the physical causes of drought?

Answer 13

• ENSO
• El Nina
• Blocking anti-cyclones
• Failure of seasonal rainfalls

Question 14

Causes of droughts - failure of seasonal rainfall

Answer 14

Some areas get low pressure for half the year and high pressure for the other half e.g rain, then dry.

But sometimes the switch between the two doesn’t happen so they wait for low pressure (rain) but it doesn’t come.

Question 15

Causes of droughts - mid-latitude blocking anticyclones

Answer 15

• Low latitudes get monsoons but mid-latitude get blocking anticyclones (high-pressure weather systems).
• Normally mid-latitudes get alternating low pressure (depressions) and high pressure (anticyclones) over days:
• Sometimes an anticyclone gets stuck over a mid-latitude stopping low pressure (rain) from entering. If this happens over a long time it causes a drought.
• Droughts in the UK develop over a year when blocking anticyclones are more common than usual. Dry winters mean a lack of groundwater recharge so the following summer has more of an impact.

Question 16

What is the ITCZ?

Answer 16

A low-pressure belt of rising air along the equator fed by the convergence of Northeast and Southeast trade winds.

Question 17

What are the stages of ITCZ?

Answer 17

1. Intense solar radiation at the Equator warms the air which rises, cools and condenses to form clouds and rain.
2. Air moves away from the Equator it cools and sinks in a belt of high pressure and hot dry conditions.
3. Air returns to ground levels and moves back towards the equator forming trade winds.
4. Trade winds meet at ITCZ where warm air rises, cools and condenses and creates convection rainfall

Position of ITCZ changes with seasons (north in June-August & South in Dec-Feb – this creates alternating wet and dry seasons in the tropics)

Question 18

What is atmospheric circulation?

Answer 18

The global atmospheric circulation model is based on cells. These cells are regions where the air moves from low pressure to high pressure. There are three cells in each hemisphere. On either side of the equator is the Hadley cell, with the Ferrell cell next and then the Polar cell at the top and bottom of the planet.

Question 19

Australia case study: Drought

Answer 19

From 1997-2009 a drought in Australia took place.

• El Nino events in 2002-2003, 2004-2005, and 2006-2007 led to especially low rainfall in South-East Australia.
• Australia has a naturally low rainfall due to the 30* South high-pressure belt that passes through it.
• Scientists think that climate change may be increasing global temperatures and changing rainfall patterns: temperatures were higher than normal during this period, resulting in more water evaporating than normal; and weather fronts that normally bring rain to South-East Australia to move further South, causing annual rainfall totals to be lower.
• The drought caused vegetation loss and soil erosion which lead to rivers and lakes suffering from outbreaks of toxic algae.
• Farmers’ incomes fell leading to over 100,000 people losing their jobs.
• Livestock died - the number of sheep in Australia fell by around 8 million during 2002-2003.
• Crop yields fell and crops that rely on irrigation were badly affected e.g rice production fell to just 2% of pre-drought totals and lead to increased food prices.

Question 20

Brazil case study: Drought

Answer 20

In 2014-2015, high-pressure systems diverted moist air further North, causing heavy rains in Bolivia and Paraguay but dry air over Brazil.

• Water rationing for 4 million people.
• Brazil relies heavily on HEP for its power, so the drought caused power cuts.
• Increased groundwater abstraction.
• A vast number of illegal wells.
• In fact, 70% of wells are illegal. Illegal wells are shallower and polluted.
• The Arabica Coffee bean crop was reduced, which drove global coffee prices up 50%.
• By 2015, main reservoirs had reached 5% of their capacity.

Question 21

The Aral Sea case study: Human causes of drought

Answer 21

The Aral Sea has progressively shrunk due to evaporation and lack of recharge by rivers. Before the Aral Sea received 2060km^3 of fresh water per year from rivers and by the early 1980s, it received none. By 2007, the Aral Sea shrunk by 10% of its original size and increased from about 1% dissolved salt to about 10% of dissolved salt.

• This has caused a variety of respiratory illnesses including tuberculosis as well as dust storms.

Question 22

The Sahel case study: Drought risk from human activity

Answer 22

Since the 1970s, the Sahel has experienced drought conditions on a regular basis. This is down to physical and human factors:

• Overgrazing and deforestation on marginal land can lead to desertification. With less vegetation there is less transpiration and evaporation from the soil, causing less rainfall.
• Changes in surrounding ocean temperature – the temperatures of the south Atlantic and Indian Oceans increased, with a smaller temperature gap between land and ocean, and monsoon rains were reduced.
• Some scientists believe climate change has reduced rainfall or made it less predictable.
• With less food being grown and an increase in demand, food prices increase.
• Increased soil erosion makes the land less fertile, creating a long-term issue for the farming community.
• Encouraging farmers to grow drought-resistant crops.
  Improving knowledge and understanding of droughts across the region by launching the Africa Climate Exchange
• Seasonal rivers and water holes dry up, so organisms which live in them or rely on them for water may die.
• Vegetation dies causing animals depending on it for food or shelter to perish or migrate.

Question 23

What are the human causes of drought?

Answer 23

Overgrazing: With less vegetation there is less transpiration and evaporation from the soil, causing less rainfall.

Deforestation: With less vegetation, changes in soil conditions through compaction and reduced soil moisture and soil retention.

Climate change: Warmer temperatures enhance evaporation, which reduces surface water and dries out soils and vegetation. This makes periods with low precipitation drier than they would be in cooler conditions. Climate change is also altering the timing of water availability.

Question 24

What is surface water flooding?

Answer 24

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

Question 25

What is groundwater flooding?

Answer 25

Flooding occurs after the ground has become saturated from prolonged heavy rainfall.

Question 26

What is Jokulhlaup?

Answer 26

A type of glacial outburst flood occurs when the dam containing a glacial lake fails.

Question 27

What is flash flooding?

Answer 27

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

Question 28

What are the physical meterological causes of flooding?

Answer 28

• Amount and type of rainfall: If it rains for a long time, the land around a river can become saturated (it’s holding as much water or moisture as can be absorbed). If there is more rainfall it cannot be soaked up, so it runs along the surface - this is known as surface run-off. If there is heavy rainfall there is less chance of it being soaked up by the soil (infiltration) so it runs off into the river. The faster the water reaches the river, the more likely it will flood.
• Relief: A steep valley is more likely to flood than a flatter valley because the rainfall will run off into the river more quickly.
• Temperature: When the temperature warms and that snow melts many days’ worth of precipitation can end up in rivers and cause flooding.
• Previous weather conditions: If it rains for a long time, the ground will become saturated and the soil will no longer be able to store water leading to increased surface runoff. However, if there have been dry conditions, water cannot infiltrate the ground due to its impermeability of the ground.
• Snowmelt: If the snow melts faster than the ground is able to absorb it, you are going to get excess water runoff. Frozen ground. Similarly, if the ground remains frozen as the snow above it melts, then it is less porous and less able to absorb the water from the snowmelt. Widespread heavy rain.
• Rock type: Permeable rocks allow water to pass through pores and cracks, whereas impermeable rocks do not. If a valley is made up of impermeable rocks, there is a higher chance of flooding as there is an increase in surface run-off.

Question 29

What are the human factors that have increased the risk of flooding?

Answer 29

• Changing land use: Impermeable areas of tarmac are located in urban areas which increases the rate of surface runoff. The speeding up of drainage of water in built-up areas via artificial conduits, such as drains and sewers, means that more water is getting to rivers faster, so in a heavy rainfall event, the lag time of a river would be very short and would be likely to flood fast.
• Mismanagement of rivers:

Channelisation: An effective way of improving river discharge and reducing flood risk. The trouble is that it simply displaces the river downstream. Some other locations may well be overwhelmed by the increased discharge

Dams: Block the flow of sediment down a river, so the reservoir gradually fills up with silt; downstream there is increased river bed erosion

River embankments: Designed to protect from floods of a given magnitude. They can fail when a flood exceeds their capacity. Inevitably, when this happens, the scale of flooding is much greater.

Meteorological offices have identified that a warming of 3C by
2070 may increase by 3.5 times the number of intense rainstorms of 30mm in one day.

Question 30

2007 flooding England and Wales case study

Answer 30

The UK has experienced some severe floods in recent years, most notably in the summer of 2007 and the winter of 2015-16. These unusually severe floods have had the same basic cause, namely prolonged heavy rainfall, but at different times of the year. During the 2016 floods, large areas of the UK received more than twice the average amount of rainfall for that time of year. Carlisle and Cockermouth in Cumbria were along the worst-hit places.

• Death and injury, 13 died and hundreds evacuated.
  -The spread of water-borne diseases
• Trauma
• Damage to property, particularly housing, 50,000 damaged.
• Disruption of transport and communications
• Interruption of water and energy supplies
• Destruction of crops and - Loss of supplies
• Disturbance of everyday life, including work 9,000 businesses effected.
• Cost local councils £140m.
• There were recriminations after the apparent inadequacy of flood protection measures. The following were singled out for blame:
• Budget cuts in the amount of money being spent on flood defences.
• An EU Directive that puts environmental conservation ahead of the regular dredging of rivers.
• Poor land management, resulting in blocked ditches.
• Global warming

Question 30

2007 flooding England and Wales case study

Answer 30

The UK has experienced some severe floods in recent years, most notably in the summer of 2007 and the winter of 2015-16. These unusually severe floods have had the same basic cause, namely prolonged heavy rainfall, but at different times of the year. During the 2016 floods, large areas of the UK received more than twice the average amount of rainfall for that time of year. Carlisle and Cockermouth in Cumbria were along the worst-hit places.

• Death and injury
  -The spread of water-borne diseases
• Trauma
• Damage to property, particularly housing
• Disruption of transport and communications
• Interruption of water and energy supplies
• Destruction of crops and - Loss of supplies
• Disturbance of everyday life, including work
• There were recriminations after the apparent inadequacy of flood protection measures. The following were singled out for blame:
• Budget cuts in the amount of money being spent on flood defences.
• An EU Directive that puts environmental conservation ahead of the regular dredging of rivers.
• Poor land management, resulting in blocked ditches.
• Global warming

Question 31

How does climate change affect the inputs of the hydrological cycle?

Answer 31

The distribution of rainfall will change and in terms of drought there will be a reduction in the inputs.

Question 31

How does climate change affect outputs?

Answer 31

Can cause initial high rates of evaporation but the impacts will be different depending on climate zone.

Question 32

How will climate change affect trends in precipitation and evaporation and how are they hard to predict?

Answer 32

Climate dynamics:

• The way the different biomes interact with each other is still a partially understood science so hard to understand whether impacts from ENSO or climate change.

Global records are very incomplete so hard to make firm predictions.

Question 33

How does climate change affect the size of snow mass?

Answer 33

Length of snow cover decreased in last 50 to 100 years as spring melt occurred earlier

Question 34

How does climate change effect size glacier mass?

Answer 34

• End of the little ice age glaciers have been retreating.
• Accelerated since the 1970s.

Question 35

How does climate change affect reservoirs, lakes and wetland storage?

Answer 35

• Regional variations linked to regional changes in climate.
• Wetland storages are changing but can’t be directly linked to climate.

Question 36

How does climate change affect the amount of permafrost?

Answer 36

• Increasing air and ocean temps leading to permafrost degradation.
• Deepening of active later release methane which creates positive feedback.

Question 37

How does climate change affect soil moisture levels?

Answer 37

Soil moisture is related to many factors climate change is just one but if precipitation increases soil moisture will likely increase.

Question 38

How does climate change affect runoff and stream flow?

Answer 38

• With more climate extremes more hydrologic extremes, more droughts and floods.
• More intense rainfall and increase in run off rates and reduce infiltration.

Question 39

Give future trends about floods:

Answer 39

• heavy precipitation lead to spectacular flooding and economic losses rising 10-fold from 1990-2010.
• Climate change may be a factor although also socio-economic factors.
• No evidence of trends in either increasing frequency.

Question 40

Give future trends about droughts:

Answer 40

• In the past 30 years droughts have become more widespread, more intense and more persistent.
• Difficult to pin down to climate change.
• Droughts affected by changes in surface temperatures.

Question 41

How do ENSO cycles affect droughts and floods?

Answer 41

• Extreme flooding in some areas and extreme drought in some.
• Therefore these also have to be considered when looking at drought.