Water Cycle Case study - Megadroughts in California and Sahel Region Flashcards
(13 cards)
What is a megadrought?
A megadrought are defined more by their duration than their severity. They are extreme dry spells that can last for a decade or longer.
What are the environmental impacts of the drought?
Environmental:
* About 1000 more wildfires than usual have occurred.
* Prolonged drought threatens wildlife.
What are the causes of the current drought?
Causes of the current drought
- In normal winters, southwest winds from the ocean deliver water. Recently, for unexplained reasons, these
winds have failed California.
- Tree ring studies: Very little of the California drought can be attributed to climate change with any certainty.
- Cooler water temperatures – known as La Niñas – tend to produce drier conditions in the west. El Niño
conditions would cause above average rainfall.
What were previous droughts in California?
Previous droughts
- Dust bowl (1930s) – Spanned 8 years in certain parts of the great plains. It was the worst American drought in the last 300 years, causing mass migration westward.
- Great plains drought (1950s) – At its peak in 1954, it covered 62% of the country.
What are the economic impacts of drought in California?
Economic:
* Last year, farmers harvested 640,000 fewer acres, but crop revenue remained strong.
* Farms have adopted more efficient water management technologies.
What are the social impacts of drought in California?
Social:
* Water shortages and restrictions.
* Competition over water supply for agriculture, domestic use and aquatic ecosystems – could escalate to conflict over water use.
However, water supplies were really stocked up prior to the drought, easing the situation.
How does drought affect California?
Impacts
* California is in the third year of one of the worst droughts in the past century.
Where is the Sahel region?
Vast semi arid region on the southern edge of the Sahara.
Human causes of drought in the Sahel region
- Population growth: rapid population growth puts pressure on the land to grow more food. Migrants fleeing from one disaster area help to make another.
- Overgrazing: too many goats, sheep and cattle destroy the vegetation cover leaving the soil left behind exposed to the wind which is then blown away, turning what was once grassland into desert
- Overcultivation: intense use of marginal land exhausts the soil and crops will not grow
- Deforestation: trees are cut down for fuel, fencing and housing. The roots no longer bind the soil, and erosion ensues.
Why is the Sahel drought sensitive
As it occupies a transitional climate zone. Under so called normal conditions, the mean annual rainfall (around 85%) is nearly all concentrated in the summer.
Why is there variability in the Sahel region
Unusually warm sea surface temperatures (SSTs) in tropical seas favour strong convectional uplift over the ocean that, in turn, weakens the West African Monsoon and contributes to drought in the Sahel.
How do humans act like a feedback loop in the Sahel
Humans enhance the impacts of drought by the over-abstraction of surface water from rivers and ponds, and of groundwater from aquifers.
What has made the situation worse in the Sahel region
The situation has been made worse by frequent civil wars.
Crops, livestock and homes have been deliberately destroyed.
