Water Flashcards
(47 cards)
1
Q
What is drought?
A
An extended period of deficient rainfall relative to the statistical multi year average for a region
2
Q
Why are the four main types of drought?
A
- Hydrological
- Socio-economic
- Meteorological
- Agricultural
3
Q
What is hydrological drought?
A
Occurs when there is deficiencies in stream flow and groundwater levels due to reduced rates of precipitation and increased evaporation.
4
Q
What is meteorological drought?
A
Shortfalls in precipitation as a result of short-term variability within the longer-term average overall.
5
Q
What is socio-economic drought?
A
Occurs when the water demand for social and economic purposes exceeds water availability. This could be the result of a weather-related shortfall in water supply or overuse of the available water supplies.
6
Q
What is agricultural drought?
A
Some farming practices, such as overgrazing, can accelerate the onset of this type of drought. Rainfall deficiency leads to deficiency in soil moisture and water availability, which has a knock-on effect on plant growth and reduces biomass.
7
Q
What are the 4 physical causes of drought?
A
- ITCZ
- Mid-Latitude Blocking Anticyclones
- Atmospheric Circulation
- El Nino/La Nina
8
Q
What is ITCZ?
A
- Belt of low atmospheric pressure located around the equator
- Moves N or S of equation seasonally
- It causes a wet season when it arrives and a dry season when it moves away
- Sometimes the sub tropical high pressure zones at the descending parts of the Hadley cell block the high humidity air masses
- This blockage can prevent the arrival of a wet season, causing a drought
9
Q
What are Mid-Latitude Blocking Anticyclones?
A
- In mid latitudes, frontal precipitation is created in low pressure systems
- This is where tropical air rises over cold, polar air
- Depressions move from West to East in the mid latitudes as a result of the Coriolis force and their track is directed by the polar front jet stream
- The loops of the jet stream occasionally stabilise, or even break up, which allow high pressure areas (anticyclones) from the sub tropics to move North
- These anticyclones bring stable weather with very little precipitation, which can persist for up to two weeks.
10
Q
What is Atmospheric Circulation?
A
- Intense solar radiation at equator warms the air, which rises cools, condenses and forms rain
- Sub -tropical high pressure zone created where air that had risen at the equator sinks to forms a belt of high air pressure, causing hot, dry conditions
Atmospheric Circulation continues at varying latitudes, either bringing wet weather, or dry weather
11
Q
When is the ITCZ above/below the equator?
A
In Northern Hemisphere:
- North of Equator in June-August
- South of Equator December-February
12
Q
What is El Nino?
A
- Trade winds weaken or even reverse
- Causes build up of warm water on West coast of South America where air rises, cools and condenses, causing more rain than usual
- East coast of Australia loses its warm water and is instead replaced with cold water
- Here, air from S America sinks, causing dry conditions leading to drought
13
Q
Human Influences on Drought:
A
- Overgrazing
- Overcultivation
- Deforestation
- Over extraction
14
Q
How does overgrazing affect drought?
A
Soil is depleted of its nutrients and stripped of its protective grass cover, leaving the soil exposed to wind and rain. Soil is eroded which then leads to desertification, where it can no longer store much water.
15
Q
How does overcultivation affect drought?
A
Reduces soil fertility and which affects the ability of crops to grow. Therefore the soil is eroded by wind and rain, losing it ability to store water
16
Q
The Sahel Drought: Background Information
A
- Has experiences at least one severe drought each century since the 17th century
- In June 2010, hottest ever temperature of 49.6*C recorded
- Drought becoming more frequent since 20th century
17
Q
The Sahel Drought: Physical Causes
A
- Sahel regions naturally experiences wet and dry seasons
- Large scale climate change triggered more frequent droughts (increases GHGs and CFCs)
- CFCs have caused a shift in the ITCZ causing normally rainy areas in Africa to become much drier
- Northern Sahel is experiencing a 30-40% annual departure from normal rainfall
18
Q
The Sahel Drought: Human Contribution
A
- Population growth in Sahelian countries doubling every 20 to 30 years
- Rainfed cropping accounts for 95% of cultivated areas in the Sahel
- Overgrazing, overcultivation and deforestation due to increase demand of population
- Rural areas rely on farming practices that are not adapted to local conditions
- Poor land management
19
Q
The Sahel Drought: Impacts
A
- From late 1960s to early 1980s, famine killed 100,000 peoples, left 750,000 dependent on food aid and affected most of the Sahel’s 50million people
- From June to August 2010, 1,200,000 were at risk of famine
- Clean water not available increasing use of contaminated water and risk of water-borne diseases like cholera
- Civil war or war between countries for water resources
- Women and children have to travel further for clean water, causing them to miss school and work
20
Q
How much pastureland and cropland has been affected in countries closest to the Sahara by the advancement of the Saharan desert S and E?
A
Pastureland- 90%
Cropland- 80%
21
Q
The Sahel Drought: Responses
A
- Growing drought resistant crops
- Improving knowledge of drought by setting up Africa Climate Exchange
- Drip irrigation to reduce water usage
- In 1995 every two out of 5 countries in the Sahel were living on foreign aid
- Food stocks carefully conserved
- Not all aid money been spent on prevent/mitigating drought. 80% has been used on infrastructure, roads and services
22
Q
Over-extraction in Australia:
A
- ‘Big Dry’ in 2006
- In Adelaide, 40% of their drinking water came from the River Murray
- River had been so over extracted that no water has flowed at the mouth
- Reservoirs also fell to 40% of their capacity as there was no precipitation to replace the over extracted water
- Australia has one of the highest per capita water consumption in the world
23
Q
How much of Australia is affected by drought in any one year due to El Nino?
A
30%
24
Q
Why are rainforests important?
A
- Source of resources, such as medicines
- Over 50% of world’s biodiversity found in the rainforest
- Contains massive amount of nutrients in the soils
25
How are rainforests affected by drought?
- Trees become stressed (drop leaves, stunted growth, susceptible to disease)
- Younger trees die, reducing canopy cover, exposing the soil and reducing soil fertility and ability to hold water
- Humidity, water vapour and rainfall is reduced
- Drying vegetation and surface tree litter can easily catch fire
- Loss of biodiversity
26
Why are wetlands important?
- Large carbon store
- Act as a giant water filter, trapping and recycling nutrients
- Used for resources and services
- High biodiversity
- Temporary water stores, mitigate river flows downstream
- Recharge aquifers
27
How are wetlands affected by drought?
- Land dries up as water evaporated with no precipitation
- Decreased biodiversity
- Cannot recharge aquifers, reducing their ability to store water
- Water left behind has increased salinity, which can lead to plant death
- Drying leads to soil erosion and reduced ability to store water
- Acts as a carbon sink
28
Pantanal Wetland Case Study:
- Large wetland covering 140,000km2 of Brazil and even more in Central South America
- Retains up to 60% of floodwater throughout the year
- Seasonal rainfalls changes it from a terrestrial to an aquatic habitat
- Aquatic and bird life rely on it for survival
- Affected by the 2014-2015 drought
- Wetland dried up
- Many bird species migrated away as could not survive
- Drought caused massive tree mortality, which meant wildlife lost their habitat
- Controlled wildfires spiralled out of control into the wetlands and surrounding forests
29
Pinon Pines Case Study:
- SW USA
- Research published in 2015 from 1300 tree sites revealed that living trees take an average of two to fours years to recover and resume normal growth following a period of drought
- Resilience to drought lower for some species, such as pines due to their high demand for water
- Between 2000 and 2003 a combination of severe drought and unusually high temperatures led to a significant die off of Pinon Pines in the Four Corners region of SW USA
- In some areas more than 90% of Pinon pines died
30
Physical causes of flooding:
- Seasonal monsoon rainfall
- Snow and ice
- Intense storms
31
How does seasonal monsoon rainfall cause flooding?
- Around 70% of average annual rainfall occurs during 100 days
- Low lying plains of large rivers especially at risk as the intense rainfall exceeds the banks full discharge as there is little lag time
- This causes the river to overflow, flooding the surrounding area
- Heavy rain also causes soil to become over saturated, meaning it cannot absorb anymore water which leads to increased surface run off
32
How does snow and ice cause flooding?
- Heavily responsible for flood events in higher latitudes or mountainous areas
- Melting snow or glaciers in late spring occurs rapidly
- Meanwhile, low layers of snow or glaciers remain frozen which means infiltration is extremely limited
- Therefore, rapid surface run off occurs towards the river basin
- Rain can also fall during rapid thaw events causing heavy flooding
- When ice dams melt, glacial lakes suddenly drain, releasing a massive volume of water at one time. This is known as a glacial outburst flood
33
How do intense storms cause flooding?
- Extreme weather, such as tropical cyclones, bring higher rates of precipitation than usual in a smaller period of time
- This can cause the soil to become waterlogged, increasing surface run off
- Lag time is decreased and the water entering the drainage basin is enough to exceed capacity so the river/lake overflows its banks, causing flash flooding
34
Human causes of flooding:
- Urbanisation
- Global warming
- Farming practices
- Deforestation
- Dams/reservoirs
- Mismanagement of rivers
35
How does urbanisation cause flooding?
- Speeding up of water drainage through drains and sewers means that a large volume of water reaches the drainage basin in a decreased period of time
- Creation of impermeable surfaces like roofs and pavements means there is less infiltration into the soil or percolation into rock
- Water that reaches river basin exceeds capacity and river overflows its banks
36
How does agriculture cause flooding?
- Removal of vegetation for other crops and reduces interception of rainfall
- This reduces lag time as surface run off is increased
- Overgrazing can lead to the soil becoming eroded due to the removal of protective vegetation
- This means less infiltration can occur as the soil loses its ability to hold water
37
How do dams/reservoirs affect flooding?
- Reservoirs are artificially created lakes, formed by building a dam across a river
- If one of these dams fails then a large volume of water can escape that the river is unable to carry flooding the surrounding land
- Sediment also builds up behind the dam which can affect the rivers flow downstream
- e.g. Uzbekistan 2020
38
How does global warming affect flooding?
- Humans contribute to the greenhouse gas layer by combusting fossil fuels and driving petrol/diesel cars
- This leads to global warming where increased evaporation can lead to areas becoming wetter to dryer, potentially causing more frequent flooding
39
Impacts of climate change on hydrological cycle inputs:
- Mode of precipitation changes
- More likely to be rain than snow
- Inputs increasing in frequency and intensity
40
Impacts of climate change on hydrological cycle flows:
- Some will increase and others will decrease
- Increased surface run off but decreased infiltration and percolation due to intense rainfall
- Also due to baked land not being able to hold water
41
Impacts of climate change on hydrological cycle stores:
- Overall decrease in size due to higher temperatures and increase evaporation
- Glaciers, permafrost melt decreasing in size
- Over extraction of ground water stores such as aquifers
42
Impacts of climate change on hydrological cycle outputs:
- Higher rates of evaporation
| - Higher rates of evapotranspiration
43
Environmental impacts of flooding:
- Recharged groundwater stores
- Increased connectivity between aquatic habitats
- Soil replenishment
- For many species, flood events trigger breeding, migration and dispersal
- Removal of soil and sediment can lead to eutrophication of water bodies
- However nutrients are flooded out of the soil
- Pollutants can be carried into water
44
Socioeconomic impacts of UK 2007 floods:
-Two people died as an indirect result of the flooding.
5,000 homes and businesses were flooded.
-48,000 homes were without electricity for two days.
-135,000 homes were without drinking water for approximately two weeks.
-825 homes were evacuated.
-10,000 motorists were stranded on county roads, including the M5 where many people remained overnight.
-It is estimated that the flooding and water crisis cost the county of Gloucestershire £50 million
45
What physical factors cause uncertainty in the hydrological cycle?
-Increases in annual temperature lead to greater -evaporation from surface water and reservoirs in -summer, although spring discharge may increase
-Greater rates of evapotranspiration, desiccation of forest stores
-Impact of oscillations, e.g. ENSO, is leading to increasingly unreliable patterns of rainfall, e.g. less predictable monsoons
-More frequent cyclone and monsoon events threaten water supplies intermittently
-Increased intensity and frequency of droughts as a result of global warming and oscillation is issue for rainfed agriculturalists
-Depleted aquifers lead to problems with groundwater
-Decreasing rainfall in many areas as a result of global warming
Loss of snow and glaciers as a store threatens many communities in mountain ares, e.g. Himalayas
46
Why does uncertainty arise?
Scientists are unable to make confident forecasts about the future availability of water.
47
Social factors causing uncertainty:
- Population growth
- Advancement in water technology/storage
- Future demand
- Global development
