Water enquiry question 2 Flashcards
What is the fundamental cause of drought?
A shortfall of water over an extended period of time.
What does drought duration do?
Increase severity
What are the possible physical causes of drought?
- Sea surface temperature anomalies are extremely important
- Teleconnections, development of weather phenomena and the impacts this can have around the globe - ENSO
What is El Niño Southern Oscillation (ENSO)?
An oscillation of the ocean atmosphere system in the tropical Pacific, having important consequences for weather around the globe.
The winds change direction blowing from West to East
Occurs every 3-6 years but appears to be getting more regular.
On a normal year there is…
- Wind direction from east to west, trade winds move warm surface water towards the western pacific
- Low air pressure in West, with rain clouds as there is warm moist air - Australia
- High air pressure in East, with upwelling of cool water (Peru current) and descending air = dry period - S. America
On an El Niño year there is…
- Wind direction from west to east, warm water moves to east.
- The cold Peru current is suppressed = poor crop
- High air pressure in West, with descending air = droughts and fires - Australia
- Low air pressure in East, with ascending air and rainclouds = more evaporation and rain and flooding - S. America
What is La Niña ?
An exaggerated version of normal conditions with very strong trade winds.
What are teleconnections?
The knock on effects around the world due to El Niño such as droughts in Brazil and floods in Kenya and Bangladesh.
What are the effects of El Niño?
- air pressure is unusually high over west coast of South America and low over Eastern Australia
- Warm water is pushed westwards so sea levels rise by up to 1m
- Strong uplift of air leads to heavy rain around Indonesia and philippines
What are the three important physical factors when concerning drought?
- El Niño
- Intertropical convergence Zone (ITCZ)
- Mid Latitude blocking anticyclones
What is the ITCZ?
Intertropical convergence zone. A band of low pressure around the equator between the northern and Southern Hemisphere Hadley Cells. This area of low pressure causes heavy rain when it is over an area and drought when it moves elsewhere.
What are mid latitude blocking anticyclones?
Areas of high pressure which rotate very slowly almost stationary in the opposite direction to cyclones.
High pressure zones over the UK blocks low pressure zones, when a polar jet stream slows anticyclones are blocked.
When were the major drought years in the UK?
1976 AND 2003
What were the effects of the 1976 drought?
temperature hit 35.9 degrees, parts of south west didn’t receive rain for 45 days, crops affected by 50%
What are the human influences on drought?
deforestation, population density, overgrazing, governance, poor agricultural techniques - irrigation, conflict which can lead to migration, soil erosion, poor infrastructure, urbanisation
What do humans act like with water usage and security in drought. (GOOD EVALUATION POINT)
a positive feedback mechanism
What were the issues in the 1999-2000 drought in Eriteria and Ethiopia?
famine
10 mil needed food assistance
war blocked access to food
population doubling every 20/30 years - pop. density
What induced the drought in Eriteria and Ethiopia?
La nina