Topic 5 - Water Cycle And Insecurity: EQ2 Flashcards
What is a drought?
An extended period of deficient rainfall relative to the statistical multi average for a region
What’s famine drought?
Food deficit
What’s agricultural drought?
Soil moisture deficit
What’s hydrological drought?
Stream flow deficit
What’s meteorological drought?
Rainfall deficit
What are the 4 physical reasons for drought?
Global atmospheric circulation
Failing of the ITCZ
Blocking high pressures
El Niño Southern Oscillation (ENSO)
How does global atmosphere circulation cause drought?
The subtropical high pressure zone is created where air that has risen at the equator has called and so sinks to form a belt of high air pressure and hot, dry conditions. It has low annual rainfall and is usually areas which are mostly deserts or grasslands due to limited moisture
How does the failing of the ITCZ cause droughts ?
The ITCZ causes air to rise due to intense solar heating, leading to high ocean evaporation and alternating wet and dry seasons. In summer, it shifts north, increasing rainfall in regions like West Africa and South Asia. In winter, it moves south, affecting areas in South America and Central Africa.
How can blocking high-pressure cause droughts?
Blocking high pressures disrupt air movement, creating stable conditions with clear skies and reduced cloud formation. They block low-pressure systems, potentially causing weeks or months of drought in mid-latitude regions like the UK. Persistent anticyclones can make it worse
How does El Niño Southern Oscillation (ENSO) cause droughts?
ENSO disrupts global weather by shifting the ITCZ and altering atmospheric circulation. El Niño warms Pacific waters every 2-7 years, moving the jet stream south and east, causing floods and droughts. La Niña cools Pacific waters, raising the jet stream and bringing Arctic-like conditions.
What is the case study for 5.4?
Sahel (2012/2013)
What are the human causes of drought in the Sahel?
Over grazing by tribes
Deforestation for fuelwood
Increasing population
Wars
Increase in farming
Soil damage
Why do humans have an impact in Sahel?
Humans act as a positive feedback loop and enhancing its impact due to social economic conditions
What is resilience?
Is the capacity of an ecosystem to drought. It is the ecosystem ability to persist in its present state despite having a deficit of water
What is a wetland?
An area of marsh, fen, peatland saturated with water permanent or seasonally. This might be static-water , flowing, fresh or salt
Why are wetland important?
Provide vital habitats to many types of plants and animals, many of which are useful to humans.
Humans depend on wetland for recreational activities such as hunting, bird watching, fishing
How do droughts affect wetlands?
Droughts have a big impact on wetland ecosystems and this can cause loss of habitats and as soil moisture is reduced they can be soil erosion and organic soils may oxidise recent carbon into the atmosphere.
Affect food web
Why are forests important?
they have ecological function such as the carbon storage, nutrient cycle, water and air purification, and maintenance of wildlife habitat, so your preservation and species habitat. They are also good for timber, food, fuel, and bio products
How do droughts affect forests?
the dryer warmer conditions lead to vegetation drying out and becoming more flammable. This makes them not very resilient as it would be hard to stop the fire once they started in the forest
What are the meteorological causes of floods?
Jet stream and low pressure weather
Monsoon (India)
Ice melt (Siberia)
How does Jet stream and low pressure weather cause floods?
Sometimes high pressure blocks the jet stream and continually delivers low pressure after low pressure to one area as there is high pressure either side
How does the monsoon in India cause floods?
The monsoon brings heavy rain over a short period of time due to moist winds condenses into rain and causes continuous rainfall
How does ice melt in Siberia cause floods?
Siberian snow melt in the spring causes extensive flooding across interiors of Asia such as the River Ob. There is a quick transformation from winter to spring, frozen ground meaning no infiltration means rapid level.
What is the case study for 5.5?
Cumbria floods in 2015
what were the (physical primary) meteorological causes of the Cumbria floods in 2015
Position of Jet stream and low
Low pressure system
Orographic rainfall
Antecedent conditions and rainfall intensity
Historic flooding
How did historic flooding events cause floods?
Storm Desmond brought 847 billion litres of rainfall over Cumbria
How did the jet stream cause floods
It was over Columbia at the time of the rainfall and cause atmospheric river and focus on Columbia
How does low pressure system cause floods
There was also a low pressure system over Columbia and this creates precipitation due to clouds
How does orographic rainfall cause floods?
Cambria is in a mountainous area so this means orographic rainfall will be there and this happens frequently
How does antecedent conditions cause floods
The rain occurred over a short period and just before that they had a storm a week before. High level of discharge
What were the secondary causes of flooding in Cumbria?
The rock type was mostly impermeable
Steep slopes of mountain means water travelled faster to rivers
Ground was already saturated so water went straight to river
What were the secondary human causes of Cumbria floods
More roads and impermeable rocks so more pressure on drains and made them overflow
Deforestation, overgrazing
Sheep farming means it’s hard for afforestation
Bad flood defences
Worst social impacts of the flood
The united biscuits factory which is the city’s biggest employer closed for weeks so many had to go with no work
3000 homes were flooded in 2005 and over 5200 in 2015
Economic impacts of the flood
the cost of the flooding was over £100 million in 2005, £270m in 2009 and £400-500m in 2015
house prices fell in flood risk areas
Environmental impacts of the flood
rivers were filled with debris and contaminated with sewage and pollutants
The saturated grounds led to landslides
Use worksheet for more data on the floods
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How does climate change have an impact on the hydrological system
Increasing anthropogenic greenhouse gas emissions
Increasing heat trapped in the atmosphere (enhanced global warming)
Increasing average air temperatures and sea surface temperatures
Hydrological variables that climate change?
Precipitation input
Soil moisture
Evaporation
Permafrost
Snow
Ice
How is the hydrological cycle changing in California?
Increased droughts
3 times as many wildfires than normal in 2014
Forecasts of mega-droughts lasting 30 years
How is the hydrological cycle changing in The Sahel?
Decline of rainfall of up to 40% between 1950 and 1990
Rains are failing due to ITCZ
What is re-greening?
Covering land with grass and trees, making it healthy again
What are the benefits of re-greening?
Natural regeneration of water-retaining shrubs and trees
Low cost reforesting
Use of water-harvesting techniques e.g. Demi-lunes
Why is there uncertainty about future flooding?
We don’t know exactly where it will get hotter (and by how much)
How would climate change lead to more floods?
For every 1 degree of temperature rise, the amount of moisture that can be held in the atmosphere rises by 7%
Creates potential for heavier precipitation and floods
What are some human influences on droughts?
Land use change
Rising population
Poor farming
Normal variability
What are some sources of uncertainty when discussing future climate change projections?
Complexity of climate systems (teleconnections)
Natural short term oscillations - e.g. ENSO cycles
Biogechemical positive and feedback mechanisms
Incomplete set of data (not collected in all locations)
How could water uncertainty lead to famine?
Not being able to adapt to different conditions may cause a famine
Additionally, people don’t know whether they need to adopt new strategies or not
