Droughts Flashcards
What is a drought?
An area drier than normal conditions— a prolonged period of abnormally low rainfall, leading to a shortage of water.
What are the main differences between an arid environment and a drought?,
Arid environment
-permanent low rainfall
-10-250mm per year
-high pressure conditions
- mostly found where Hadley cells and ferrel cells meet
Droughts
-temporary low precipitation <0.2mm
-(in the Uk) drought is 15 consecutive days without rainfall
-global
-high pressure as well
State the 3 human causes to droughts
Dams, déforestation and agriculture
What are dams?
They are large structures built on rivers to act as flood defences, so create reservoirs as stores for water, to use in industry / agriculture and recreation.
What do dams produce?
Hydro-electrical power
Why do dams contribute to drought formations?
By storing large amounts of water upstream, the amount of water further down is reduced significantly if the water is not continuously flowing. This leaves areas in drought as the water levels have dropped.
What is deforestation?
The permanent removal of widespread trees in a location for constructional or resource purposes.
How does deforestation contribute to droughts forming?
Removing trees reduces less absorption of CO² leads to an increase in greenhouse gas emissions, influencing climate change / global warming. Without transpiration, the water cycle is disrupted hindering the processes: condensation + precipitation. Therefore, less rainfall occurs as there aren’t photosynthesising plants.
What are impacts of drought on agriculture
Low crop yields, crop failures and loss of livestock.
How does agricultural irrigation cause droughts?
Ways of irrigation, such as pumping from wetter areas, rivers or groundwater sources contributed to a lack of water in that area over time. This leads to lowered water supplies increasing droughts and worsening its effects.
State the two natural causes of droughts.
Meteorological and hydrological causes
What is the cause to droughts — meteorological?
when the amount of precipitation received in a specific area is less than the average
Why is an area like the Sahara not in a drought?
The conditions are normal for that climate, precipitation levels etc.
What are three defects to meteorological droughts?
Circulation levels vary which cause disruptions.
Changes in normal weather patterns can lead to climate change.
Atmospheric and oceanic circulation systems disrupted.
What causes changes to oceanic / atmospheric circulation?
Warmer temperatures than usual
What do jet streams divert?
Weather systems like rainy seasons.
What is the cause to droughts — hydrological?
This is when reduced precipitation impacts water supply, e.g there is decreased streamflow, soil moisture, reservoir, lake levels, and groundwater supplies.
State the differences between meteorological and hydrological drought causes.
Meteorological
- occurs before hydrological
-this is a lacking of rain
-lack of rain affects photosynthesis, food growth etc
Hydrological
-occurs resultant to the shortage in rain
-lack of rain affects a hydrological store of water.
-less obvious effects
What happens to the water cycle when there is a drought?
the flow of streams and rivers declines, water levels in lakes and reservoirs fall, and the depth to water in wells increases
Why does water monitoring take months to see changes with hydrological droughts?
The effects are prolongedly seen afterwards due to various reasons - lack of management or supervision in an area of flowing water, levels of water are not documented.
Why does water in rivers and other flowing sources become harder to access with hydrological droughts?
The water begins to enter permeable rocks and soil as there is a lack of precipitation (meteorological droughts). This means that river levels drop and an over-dependance on groundwater / reservoir sources is developed.
