The water cycle and water insecurity - What factors influence the hydrological system over short- and long-term timescales? Flashcards
What are short-term deficits within the hydrological cycle (i.e. droughts) the result of?
Short-term deficits within the hydrological cycle (i.e. droughts) are the result of physical processes, but can have significant impacts on people.
What are short-term surpluses within the hydrological cycle (i.e. floods) the outcome of?
Short-term surpluses within the hydrological cycle (i.e. floods) are the outcome of physical processes and can have significant impacts on people.
In the longer term, what can climate change have a significant impact on?
In the longer term, climate change can have a significant impact on the hydrological cycle, both globally and locally.
What is the definition of a drought?
Drought is defined in meteorological terms as a shortfall or deficiency of water over an extended period, usually at least a season.
What is a hydrological drought characterised by?
Meteorological drought is sometimes distinguished from hydrological drought. The latter is characterised by reduced stream flow, lowered groundwater levels and reduced water stores.
What is the impact if a drought can and does hit agricultural productivity hard?
This, in turn, can lead quickly to food shortages, famine and starvation.
What does research suggest that sea surface temperature anomalies are an important causal factor in?
Short-term precipitation deficits
What do sea surface temperature anomalies relate to?
Sea surface temperature anomalies relate to how much temperatures of the sea surface, recorded at a particular time, differ from the long-term average. Anomalies may be positive or negative. A positive anomaly occurs when the observed temperature is warmer than the average. A negative anomaly is when the observed temperature is cooler than the average.
What do temperature anomalies provide the key to, which, in turn, is thought to trigger the occurrence of droughts?
El Nino-Southern Oscillation (ENSO)
What happens to conditions during an El Niño event?
When this happens, cool water normally found along the coast of Peru is replaced by warmer water.
At the same time, the area of warmer water further west, near Australia and Indonesia, is replaced by cooler water.
What happens to cool water normally found along the coast of Peru during an El Niño event?
Cool water normally found along the coast of Peru is replaced by warmer water.
What happens to the area of warmer water further west, near Australia and Indonesia during an El Niño event?
The area of warmer water further west, near Australia and Indonesia, is replaced by cooler water.
How often do El Niño events usually occur?
El Niño events usually occur every three to seven years and usually last for 18 months.
Explain how El Niño episodes contribute to drought conditions.
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What do La Niña episodes involve?
They involve the build-up of the cooler-than-usual subsurface water in the tropical part of the Pacific.
What does the build-up of cooler-than-usual subsurface water in the tropical part of the Pacific in La Niña episodes lead to?
This situation can also lead to severe drought conditions, particularly on the western coast of South America.
Explain how La Niña episodes contribute to drought conditions.
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Which part of the globe is most affected by (a) El Niño events, and (b) La Niña episodes?
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A normal year
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An El Niño year
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An La Niña year
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What is desertification?
Desertification is the process by which once-productive land gradually changes into a desert-like landscape. It usually takes place in semi-arid land on the edges of existing deserts. The process is not necessarily irreversible.
What causes desertification?
The causes of desertification are essentially natural. They set in motion a downward spiral that runs roughly as follows:
- changing rainfall patterns with rainfall becoming less reliable, seasonally and annually. The occasional drought year sometimes extends to several years
- the vegetation cover becomes stressed and begins to die, leaving bare soil
- the bare soil is eroded by wind and an occasional intense shower
- when rain does fall, it is often only for very short, intense periods. This makes it difficult for the remaining soil to capture and store it
Explain why human factors do not cause drought but they act like a feedback loop.
Humans enhance the impacts of droughts by the over-abstraction of surface water from rivers and ponds, and of groundwater from aquifers.
What are the four human factors contributing to desertification?
Key human factors encouraging this are:
- population growth
- overgrazing
- over-cultivation
- deforestation.
How does population growth contribute to desertification?
Rapid population growth puts pressure on the land to grow more food. Migrants fleeing from one disaster area help to make another
How does overgrazing contribute to desertification?
Too many goats, sheep and cattle destroy the vegetation cover
How does over-cultivation contribute to desertification?
Intense use of marginal land exhausts the soil and crops will not grow
How does deforestation contribute to desertification?
Trees are cut down for fuel, fencing and housing. The roots no longer bind the soil and erosion ensues
In the case of the Sahel, how has the situation of desertification been made worse?
In the case of the Sahel, the situation has been made worse by frequent civil wars.
What are the impacts of desertification in the Sahel?
Crops, livestock and homes have been deliberately destroyed.
Of the four human factors contributing to desertification, which do you think is the most significant?
Deforestation