Topic 5 - Water EQ2 Flashcards
Explain briefly what a drought is ?
Droughts exist when there is a water deficit in a particular place over a period of time, compared to the average rainfall for that same period - 3 main types
- described has having a slow onset, as they develop gradually
What are the three types for droughts?
- agricultural
- hydrological
- meteorological
What are meteorological droughts, what’s are the 5 features?
Caused by a rainfall deficit - features include:
- low precipitation
- high temperatures
- strong winds
- increased solar radiation
- reduced snow cover
What are the impacts of meteorological droughts - give 3?
-loss of soil moisture
- irrigation supply drops
- reduction in water available for consumption
What are hydrological droughts, what’s are the 5 features?
Caused by stream flow deficit - features include:
- reduced infiltration
- low soil moisture
- little percolation and groundwater recharge
What are the impacts of hydrological droughts - give 3?
- reduced storage in lakes and resevoirs
- less water for urban supply
- threats to wetlands and habitats
What are agricultural droughts, what’s are the 3 features?
Caused by soil moisture deficit - features include:
- low evapotranspiration
- reduced biomass
- fall in groundwater level
What are the impacts of agricultural droughts - give 4?
- poor yield from rainfed crops
- failing irrigation systems
- rural industries affect
- government aid may be required
What are socio-economic droughts, what’s are the 4 features?
Caused by a food deficit - features include:
- loss of vegetation
- increased risk of wildfires
- soil erosion
- desertification
What are the impacts of socio-economic droughts - give 4?
- rural economy collapses
- rural to urban migration
- international aid required
- humanitarian crisis
Give the full definition of a drought
A drought is an extended period (season, year, several years) of deficient rainfall relative to the statistical multi year average for a region
Briefly explain the global atmospheric circulation - include steps 1,2 and 3?
1) intense solar radiation at the equator (ITCZ) warms air - air rises,cools and forms clouds and rain
2) subtropical high-pressure zone is created where air that had risen at the equator cools and sinks
3)air returns to ground at the equator, creating trade winds (caused by Coriolis effect)
Briefly explain the global atmospheric circulation - include steps 4,5 and 6?
4) trade winds meet at the intertropical convergence zone where warm air rises - position of ITCZ moves with the seasons
5)warm air moving from the subtropics to mid-lattitudes meets cold polar air - warm less dense air rises, causing rainfall
6)warmer air rises into polar front jet stream - transferred to poles where it cools,sinks and moves back to the equator
Explain what the intertropical convergence zone (ITCZ) is?
A belt of low atmospheric pressure located around the equator (moves north or south seasonally) - evaporation form oceans and air rising at the ITCZ due to heating from sun causes an alternating wet season (when it arrives) and dry season (when it moves away) in some world regions
Explain why the ITCZ alternates seasonally?
Moves north of south of the equator seasonally - for example its further north during the northern hemisphere summer
Explain how the ITCZ can be modified?
Subtropical high-pressure zones (associated with descending convection cells, Hadley cells) block the high humidity, rain-bearing air masses associated with the ITCZ modifying the pattern
Explain how a severe drought could occur in Sahel?
Over continental areas such as Africa there may be lower humidity levels because less water evaporates, if high pressure zones block the arrival of the wet season, a severe drought can occur
Explain what occurs during low pressure (depression) and any weather associated with it?
air rises cools and the water vapour condenses to form clouds and possibly precipitation - weather is often unsettled with various weather fronts associated with depression
Explain what occurs during high pressure (anticyclone) and any weather associated with it?
air is descending, which reduces the formation of clouds and leads to light winds and settled weather conditions
Give 3 physical causes of droughts?
- global atmospheric circulation
- ITCZ being blocked by high pressure
- mid latitude blocking anticyclones (high pressure)
Explain what happens in an anticyclone?
Large-scale circulation of high pressure - the centre has very high pressure which makes it heavier causing the air to sink to the surface and become drier - when its at the surface it moves away from the centre in a clockwise rotation in the NH and counterclockwise in the SH
- dry and fair weather
What weather conditions come with anticyclones?
Anticyclones typically result in stable,fine weather,with clear skies
- little precipitation
Explain the main difference between cyclones and anticyclones?
- Cyclones are areas of low pressure where the air moves counterclockwise in the Northern Hemisphere, and clockwise in the Southern Hemisphere
- An anticyclone is associated with high pressure and its winds move clockwise in the Northern Hemisphere, and counterclockwise in the Southern Hemisphere.
Explain how droughts are caused in mid-latitude countries referencing anticyclones and depressions?
Depressions move from west to east in the mad-latitudes due to coriolis effect, their path is directed by the polar front jet stream - the loops of the jet stream occasionally break up, allowing anticyclones from the subtropics to move northwards bringing with them low precipitation and heat waves
- rain bearing depressions are forced around them - usually to north but occasionally south - causing droughts in mid latitude counties (eg UK)
Explain why anticyclones are able to block weather systems for relatively long periods?
The stability of anticyclones with their sinking air and calm conditions means they can persist and block weather system from the west for up to two weeks
- if the situation is repeated over the space of a few months normal precipitation levels are greatly reduced and may lead to droughts
Give an example of blocking anticyclones disruption mid-latitude regions?
Met office reported that from 2010 to 2012 much of central,eastern and southern England and Wales expirenced a prolonged period of below-average rainfall due to blocking anticyclones
Explain what the El Niño-southern oscillations is (ENSO)?
The ENSO cycle is the movement of warm water mass in the equatorial Pacific Ocean, it occurs due to the changes in the trade winds,atmospheric circulation and ocean currents
- there are two phases: El Niño and La Niña
Explain what El Niño is, what are the conditions?
Warming of sea surface temperatures with occurs every 2-7 years (concentrated in the central-east equatorial pacific) peak is usually December
- El Niño is declared when sea temperate in the tropical eastern pacific rise 0.5 degrees above the long term average leading to warmer weather in that region
What does El Niño result in, give the expected weather?
The warmer waters can cause the pacific jet stream to move south from its neutral position resulting in dryer and warmer than usual conditions in northern Us and Canada
- the warmer water results in more precipitation
Explain El Niños effect on the western pacific?
El Niño reduces evaporation in the western pacific as water is cooler- so the affected countries experience droughts, for example Australia and Indonesia
Causes of El Niño - give 2?
- In a non-El Niño year there is descending air over eastern pacific and rising warm moist air over the western pacific
- in an El Niño year the trade winds are reduced or reverse (going west to east) leading to a reversal of the conditions and rising air over the eastern pacific and descending over the western pacific
What is La Niña?
Occurs when sea temperatures fall below average which brings cooler and drier than average weather in the eastern pacific
- occurs every 3-5 years
Explain a cause of La Niña?
Stronger than usual eastward trade winds and ocean currents which bring cold water to the surface through upwelling