Water Flashcards
what are the 4 types of drought?
meteorological drought- when long-term precipitation is lower than normal
agricultural drought- where there is insufficient soil moisture to meet the crops needs
hydrological drought- deficiencies in surface and subsurface supplies (rivers, reservoirs, lakes, groundwater), can lead to salinisation in high temps
socio-economic/famine drought- widespread failure of crops and natural vegetation, demand greater than supply
it goes in this order in when they occur
what is the UN’s definition of a drought?
an extended period of deficient rainfall relative to the average for an area. it is a slow onset hazard.
what are the 3 meteorological causes of drought?
- global atmospheric circulation system and the ITCZ (longer term)
- mid latitude blocking anticyclones (shorter term)
- el nino southern oscillation cycle (ENSO)
explain the difference between short term and long term precipitation deficits
shorter term may be mid latitude blocking anticyclones or sea surface temperature anomalies and long term trends may be those that are associated with climate change or the ITCZ
explain the role of global atmospheric circulation in influencing drought
areas 30º north and south are drought prone due to warm and clear skies through high pressure.
- sometimes the sub tropical ridge associated with the descending Hadley cell air blocks the high humidity, rain bearing air masses that arrive with the ITCZ.
- this is because it is dense and stable.
- this can cause severe droughts like in the Sahel and is generally worse 30º north
- climate change may increase this by reducing the temperature difference between land and sea
explain the role of mid blocking cyclones in influencing drought
normally in the mid latitudes (UK) frontal precipitation is created in low pressure systems that form along the polar front where warm tropical air rises over cold polar air
- when the jetstream loops north of the UK, high pressure areas (anticyclones) from the subtropics can move northwards, this ‘blocking’ anticyclone is able to block the passage of the jetstream which brings depressions to the UK
- the stability of the anticyclones means that due to the sinking air and calm conditions they can persist and block weather systems from the west for up to two weeks, if this happens a lot it can cause drought
- from 2010-2012 England and Wales saw a prolonged period of below-average rainfall due to blocking anticyclones leading to:
- raging wildfires in NW Scotland as peat lands dried out
- in autumn 2011 farmers struggled to harvest crops
what are depressions?
they move from west to east in the mid-latitudes as a result of the Coriolis force and their track is diverted by the polar front jet stream which is a very fast moving belt of air in the upper troposphere, these depressions are forced normally to the north but also to the south
what are features of an anticyclone?
- upwards/rising air
- clockwise, light/calm winds
- high pressure
- dry weather
- very stable, not easily moved and can stay put for several weeks
what is the ENSO cycle?
It refers to the coupled ocean-atmospheric cycle where a large mass of warm water in the equatorial Pacific alters its position during the cycle. (normally happens at Christmas)
what are the normal conditions in the Pacific basin compared to those during an El Nino?
normal conditions:
- trade winds blow from east to west along the equator
- the air pushes the warm moist air westwards to Indonesia and the cold dry air to South America
- the warmer air in the west results in low pressure and in the east the air cools and sinks creating high pressure
- warm, moist air rises, cools and condenses forming rain clouds
- thermocline, upwelling
el nino:
- the air circulation loop is reversed with air moving from west to east and so Peru gets wetter due to warm air and Indonesia gets dryer due to colder air leading to forest fires and droughts.
- the trade winds get weaker and warm surface water drifts across the Pacific towards S America leading to a drought in the west
- less upwelling of cold on east, cancels out normal temp difference
- it impacts the tropics the most
what happens in a La Nina?
- a flip side in oscillations and trade winds strengthen and so this leads to the ocean become colder with more upwelling in the east and warmer oceans in the west
- this leads to enhanced conditions where water is colder than normal in the tropical part of the pacific.
- this can lead to severe drought conditions especially along the western coast of South America, usually follows after an el Nino event and there is very warm water moving east to west with very strong air circulation
- Peru gets even dryer than it would be, asia gets even wetter
explain what teleconnections are
it refers to the climate anomalies that relate to each other over large distances
ENSO cycles have been connected with climate anomalies across the world
teleconnections in el niño show dry weather in western pacific from June to January and eastern Pacific between the band of dry weather sees wet weather from June to April
- el nino has also created dryer conditions in south Africa and india
this is reversed in a la Nina where the band in western Pacific becoming wet and the band to the east becoming dry
- la nina has created dryer conditions in the Middle East and southern USA
areas wet in el niño will be dry in la Nina
how do the teleconnections from and el nino/la Nina affect the hydro cycle?
el nino
- the drier climate means there will be reduced evapotranspiration after reaching deficit and therefore lower soil moisture, and lower river discharge, this will lead to agricultural drought
la nina
- western pacific sees higher soil moisture therefore resulting in higher levels of surface run off (saturated and infiltration excess overland flow) which in turn leads to a higher discharge of rivers
give statistics on drought and food shortages as a result of enso
- Britain have pledged £45million of emergency support for 2.6 million people and food for up to 120,000 malnourished children in Ethiopia and elsewhere
- one of the worst affected areas is likely to be Malawi where the worst drought in almost 10 years is expected to cause further severe malnutrition
- unicef said it expected 8.5 million people in Ethiopia to need food aid and several million more in Somalia and Kenya
explain the 2015 el nino
- the concentrated rain bands account for 40% of California’s water supply
- it reduces rainfall in their wet seasons and less rain means drier vegetation and drier air which makes forests more vulnerable to forest fires
- the 2015 el Nino was scheduled to be the strongest since 1997-98
- people wonder whether it would have brought significant rainfall to drought-plagued California
what will happen with el ninos and climate change?
- some suggest that super el ninos events could double in the future due to CC
- scientists are predicting that extreme el Nino events could occur every 10 years instead of every 20
- some suggest the enso cycle will become more intense, others say it will weaken and some say it wont change
- the interaction of them means that the el Nino events may be stronger than ever
explain the Indian monsoon in a changing climate
- an increase in monsoon rainfall on a seasonal mean, area-average basis, due to the twin drivers of an increasing land-sea thermal contrast and the warming over the indian ocean which allows more moisture to be carried to India
- a 5-10% change in rainfall, can influence agricultural production and the stocks and commodities market
- a break in monsoon rains sees cuts of up to 50% in some cases of their normal rainfall, leading to cuts in agricultural output and declining GDP
- 2013 floods in asia
what is an el nino? (brief)
warm surface water in the pacific that is normally kept on the west as a result of trade winds, moves east across the Pacific Ocean
what is a la Nina? (brief)
a more intense version of normal conditions in the pacific when trade winds are intensified and warm surface water is pushed further west, allowing colder water to upwell and move further west across the ocean, causing drought in South America. this usually follows an el Nino event
how will climate change affect inputs and outputs within the hydrological cycle?
precipitation
- a warmer atmosphere has a greater water-holding capacity
- precipitation to increase in tropics and high latitudes and will decrease 10-30º north and south of the equator as conditions strengthen
- widespread increases in rainfall intensity due to increase in moisture in the troposphere and so the higher water vapour concentration leads to intense rainfall events
- rainfall intensity rise
- fall in the long term
due to lack of evaporation due to dieback from dry weather in the long term
- threat of tipping point of the amazon dieback, between 30 and 60% of the amazon could become a dry savannah leading to forest loss and further problems with precipitation
evaporation
- evaporation rates to increase due to warmer temps leading to higher water vapour concentration leading to intense rainfall events
- transpiration is linked to vegetation changes which in turn are linked to changes in soil moisture and precipitation
what stores and flows will be impacted by climate change?
- runoff (flow) leading to flooding
- soil moisture stores leading to drought
- size of snow and glacier mass
- reservoir, lake and wetland storage
- permafrost