9.causes of droughts
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The Causes and Effects of Drought
LO: To understand the causes of anti-cyclonic weather and the global distribution of droughts.
Starter Activity:Write down all the ways in which we
use water every day.Which ones could
you not do without?Which ones are
easier to cut down on?
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What is a drought?• Look at the pictures and come up with a
definition of your own.
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A lack or of for an unusually
period of , involving less than the
usual over 3 months
A lack or shortage of water for an unusually long period of time, involving 50% less than the usual rainfall over 3 months
A good definition for drought
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A drought is
A reduction in precipitation over an extendedperiod of time. (lack of rainfall)
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‘Effective precipitation’
The difference between actual precipitation andevapo-transpiration.
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What’s different about a drought compared to a hurricane, earthquake or volcano?
(apart from the obvious!)
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Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec0
50
100
150
200
250
300
350
400
450
500Rainfall in Southern Spain
Months
Rain
fall
or e
vapo
tran
spir
ation
in m
mEvapotranspirationRainfall Q: Explain which months Spain is at risk
of severe drought.
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Droughts. So where do you think?
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Where do the droughts occur?
Arid Semi Arid
http://drought.mssl.ucl.ac.uk/drought.html?map=%2Fwww%2Fdrought%2Fweb_pages%2Fdrought.map&program=%2Fcgi-bin%2Fmapserv&root=%2Fwww%2Fdrought2%2F&map_web_imagepath=%2Ftmp%2F&map_web_imageurl=%2Ftmp%2F&map_web_template=%2Fdrought.html
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Some areas are more at risk than others...
Arid + High Density = High Risk
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Use the atlas to gather population density data and then write a description of the distribution of droughts globally considering the potential risk to the areas below. (Arid + High Density = High Risk)
Arid Semi Arid
North America
South America
Africa
Asia
Oceania
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How might these factors affect the severity of a drought?
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Mix and match
• Complete the sheet to show all the different factors that affect the severity of drought.
• Extension question: how might the effects of drought be different in an LEDC and an MEDC?