a reversal of winds and ocean...
TRANSCRIPT
QU: What are the meteorological causes of drought?AIM: To explain temporal scale factors that create drought conditions. Starter: The 12 statements below can be grouped in threes under the headings in blue. Find the groups.
Drought
Aridity
El Nino Souther Occillation
A temporary phenomenon
A permanent condition
A human induced condition
overgrazing and excessive water
extraction
Long period of belowaverage rainfall.
Uncertain frequency
When low precipitation is normal
And write them down
Desertification
A reversal of winds and ocean currents
Occurs in equatorial Pacific
UK Water Budget Temperate Climate Drought an extended period of this.
Due to disruptions in this.
Meteorological drought (2)
Hydrological drought (3)
Agricultural drought (3)
SocioEconomic drought (2)
Lack of or reduction in long term precipitation
Differs across the world as precipitation levels vary.
Lack of or reduced surface water and groundwater flows.
Can occur after meteorological drought conditions end. Delayed.
Can take longer to end as stores need torecharge.
Comes after Meteorological droughts but before Hydrological droughts*.
Lack of moisture in the soil, oftendue to lack of rainfall.
Often results in stress to vegetationand crops.
TASK: 1 Write the heading, Types of drought. In pairs allocate the statements in the envelope to the correct heading. (Number of statements in brackets) You will get a correct copy to stick in your notes.
Occurs when demand outstrips supply.
Differs from other droughts as it does not necessarily need a meteorological drought to trigger it.
2 Explain the * statement.
Ext: In what sort of area would you expect SocioEconomic droughts?Justify your answer.
Meteorological drought
Hydrological drought
Agricultural drought
Lack of or reduction in long term precipitation
Differs across the world as precipitation levels vary.
Lack of or reduced surface water and groundwater flows.
Can occur after meteorological drought conditions end. Delayed.
Can take longer to end as stores need torecharge.
Comes after Meteorological droughts but before Hydrological droughts*.
Lack of moisture in the soil, oftendue to lack of rainfall.Often results in stress to vegetationand crops.
Socioeconomic droughtOccurs when demand outstrips supply.
Differs from other droughts as it does not necessarily need a meteorological drought to trigger it.
Answers
El Nino Southern Oscillation Cycles of the Pacific Ocean have a global influence on rainfall patterns. (Spatial scale) The El Nino and El Nina events can also last a considerable time. (Temporal Scale) These cycles are a major meterological influence.
To understand how significant ENSO cycles are you need to know some basics of normal atmospheric patterns of rainfall, due to global circulation patterns.
ENSO CYCLES
= desert
Deserts
Equator
Tropic of Cancer
Tropic of Capricorn
Describe the distribution of regions that receive very heavy rainfall. Offer a reason for this.
Describe the distribution of world deserts. Can you offer a reason for this? No? After the next clip you will.
General trends of global rainfall
Ext: Droughts rarely occur within deserts Why?
TASK:
Episode 1: 26:33 34:50 (8 mins) TASK: Complete your copy of these notes.
1. Why is the warm rising air (Low Pressure) at the equator drawn towards the poles?
2. Why doesn't reach the poles directly?
3. Why does the air sink at approx 300 N/S? (High Pressure)
4. What world biome is created at this latitude as a result?
5. What characterises/defines deserts? Why is this the case at this latitude?
6. What then happens to the air next? Why?
7. What regular surface winds does this create?
8. In total, how many 'Atmospheric Circulation Cells' are there in the each Hemisphere?
9. Why do you think it is called Low and High Pressure? Think in what direction air is moving in relation to the surface of the Earth.
10. Is it this simple? The positioning of rising and sinking air between the atmospheric cells (bringing rain or dry conditions) can vary greatly. It is this that can create water surplus (____________) or water deficits (______________) globally for long or short periods of ____________ or over small or wide areas.
TASK: You have a copy of the next two slides. READ the information
carefully.
Then complete the questions on the sheet. Stickin your own copy of the cycle diagrams.
ENSO CYCLESENSO CYCLES are deviations from the normal models of Atmospheric and Oceanic circulation. They can create droughts and floods in different areas of the world in turn.
La Nina
HighPressure
Low Pressure
El Nino
HighPressure Low
Pressure
'Normal years' Winds travel westward across the surface of the Pacific, taking warm surface water with them. Cold water rises up off S. America to replace the warm water that has travelled west with the winds. This is also dragged west by winds and warms. Eventually the moist warm air rises in the west just off Australasia creating Low Pressure and rains. The air returns east in the atmosphere the and sinks over western regions of S. America creating dry weather. (This is responsible for the Atacama desert in Peru).
La Nina is an intensification of these 'Normal' conditions with super intense rainfall events in Australasia and prolonged dry, drought periods in S.America.
El Nino events are a complete reversal of 'normal conditions'. Warmer waters develop in the Eastern Pacific, just off S.America. This creates rising air and low pressure which drags surface winds in reverse across the Pacific so they head east. This creates rains and floods in S. America. Meanwhile the rising air heads west and sinks over Australasia creating high pressure and dry, drought conditions. Wildfires also occur across swathes of Australia.
El Nino and La Nina events are hard to predict and can last several years. They also disrupt weathers systems globally so their significance should not be under estimated.
Typical Global Variations in Rainfall due to La Nina
Typical Global Variations in Rainfall due to El Nino
1 Referring to the Pacific region only describe and explain the distribution of drought caused by La Nina.
2 Referring to the Pacific region only describe and explain the distribution of drought caused by El Nino.
EXT: Outline wider global changes caused by ENSO cycles.
El NinoSouthern Oscillation (ENSO Cycle). Normally there is warm water off the coast of Australia and cool water off the coast of S.America. Trade winds carry moist air from East to West resulting in rain along the Australian coast DecFeb. El Nino is a complete reversal of this pattern that happens every 25 years leading to rain and flooding in Peru and drought in Australia.
Human mismanagement of an environment. Over extraction of ground water or deforestation leading to changing rainfall patterns can also cause water shortages and desertification.
Persistent high pressure systems. Cool sinking air brings clear skies and sunny conditions to a region. If these last long enough then reservoirs and ground water supplies can run low leading to drought. The jets stream can play a part here with the UK.
Unusual changes to seasonal rains caused by changes to prevailing wind tracks can mean moist air is not blown over a land mass or not blown far enough north. This can mean reservoirs and groundwater supplies are not recharged leading to drought.
Drought is characterised by a long period of below average rain for theenvironment affected. This situation is temporary.
Drought can be caused by four main situations
Plenary: Stick in your copy of this information.Comment on the potential spatial and temporal extent of each. (scale)
Dry
Wet
Wet
Wet
Dry
Dry
Dry
Atmospheric Circulation1. Why is the warm rising air (Low Pressure) at the equator drawn towards the poles?
2. Why doesn't reach the poles directly?
3. Why does the air sink at approx 300 N/S? (High Pressure)
4. What world biome is created at this latitude as a result?
5. What characterises/defines deserts? Why is this the case at this latitude?
6. What then happens to the air next? Why?
7. What regular surface winds does this create?
8. In total, how many 'Atmospheric Circulation Cells' are there in the each Hemisphere?
9. Why do you think it is called Low and High Pressure? Think in what direction air is moving in relation to the surface of the Earth.
10. Is it this simple? The positioning of rising and sinking air between the atmospheric cells (bringing rain or dry conditions) can vary greatly. It is this that can create water surplus (____________) or water deficits (______________) globally for long or short periods of ____________ or over small or wide areas.
El NinoSouthern Oscillation (ENSO Cycle). Normally there is warm water off the coast of Australia and cool water off the coast of S.America. Trade winds carry moist air from East to West resulting in rain along the Australian coast DecFeb. El Nino is a complete reversal of this pattern that happens every 25 years leading to rain and flooding in Peru and drought in Australia.
Human mismanagement of an environment. Over extraction of ground water or deforestation leading to changing rainfall patterns can also cause water shortages and desertification.
Persistent high pressure systems. Cool sinking air brings clear skies and sunny conditions to a region. If these last long enough then reservoirs and ground water supplies can run low leading to drought. The jets stream can play a part here with the UK.
Unusual changes to seasonal rains caused by changes to prevailing wind tracks can mean moist air is not blown over a land mass or not blown far enough north. This can mean reservoirs and groundwater supplies are not recharged leading to drought.
Drought is characterised by a long period of below average rain for theenvironment affected. This situation is temporary.
Drought can be caused by four main situations
El NinoSouthern Oscillation (ENSO Cycle). Normally there is warm water off the coast of Australia and cool water off the coast of S.America. Trade winds carry moist air from East to West resulting in rain along the Australian coast DecFeb. El Nino is a complete reversal of this pattern that happens every 25 years leading to rain and flooding in Peru and drought in Australia.
Human mismanagement of an environment. Over extraction of ground water or deforestation leading to changing rainfall patterns can also cause water shortages and desertification.
Persistent high pressure systems. Cool sinking air brings clear skies and sunny conditions to a region. If these last long enough then reservoirs and ground water supplies can run low leading to drought. The jets stream can play a part here with the UK.
Unusual changes to seasonal rains caused by changes to prevailing wind tracks can mean moist air is not blown over a land mass or not blown far enough north. This can mean reservoirs and groundwater supplies are not recharged leading to drought.
Drought is characterised by a long period of below average rain for theenvironment affected. This situation is temporary.
Drought can be caused by four main situations
Lack of or reduction in long term precipitation
Differs across the world as precipitation levels vary.
Lack of or reduced surface water and groundwater flows.
Can occur after meteorological drought conditions end. Delayed.
Can take longer to end as stores need to recharge.
Comes after Meteorological droughts but before Hydrological droughts*.Lack of moisture in the soil, oftendue to lack of rainfall.Often results in stress to vegetationand crops.
Socioeconomic droughtOccurs when demand outstrips supply.Differs from other droughts as it does not necessarily need a meteorological drought to trigger it.
Agricultural drought
Hydrological drought
Meteorological drought
Lack of or reduction in long term precipitation
Differs across the world as precipitation levels vary.
Lack of or reduced surface water and groundwater flows.
Can occur after meteorological drought conditions end. Delayed.
Can take longer to end as stores need to recharge.
Comes after Meteorological droughts but before Hydrological droughts*.
Lack of moisture in the soil, often due to lack of rainfall.
Often results in stress to vegetation and crops.
Occurs when demand outstrips supply.
Differs from other droughts as it does not necessarily need a meteorological drought to trigger it.
Agricultural drought (3) Socioeconomic drought (2)
Hydrological drought (3)
Meteorological drought
Statements to print for envelopes