Water - EQ2 - Flashcards
Define drought
- an extended period (a season, year or several) of deficient rainfall relative to the statistical multi year average for a region
An im…… of ….&…. of water can have serious implications for the hydrological cycle
- imbalance
- inputs & outputs
A ….. (more commonly known as a drought) refers to when input is less than output
- deficit
What are the 5 key types of drought
- socio-economic
- agricultural
- meteorlogical
- hydrological
- ecological
Define meteorlogical drought
- a shortfall or deficiency of water over an extended period, usually at least a season
What are the features of meteorlogical drought
- Rainfall deficit
- Low precipitation
- High temperatures
- Strong winds
- Increased solar radiation
- Reduced snow cover
What are some explicit impacts of meteorlogical drought
- Loss of soil moisture
- Irrigation supply drops
- Reduction in water available for consumption
Causes of meteorlogical drought
- Droughts can range from …………..&……….precipitation deficits to longer-term trends that are part of …………………
- Droughts can range from** short-term and localised** precipitation deficits to longer-term trends that are part of climate change
Causes of meteorlogical drought
- Research suggests that …………………………… are an important causal factor in short-term precipitation deficits
- Research suggests that sea surface temperature anomalies are an important causal factor in short-term precipitation deficits.
Causes of meteorlogical drought
- The physical causes of drought are only ………. understood
- They lie somewhere in the complex interactions between ……. , ……. , …….. , …… & ……, which produces the climates of the globe
- The physical causes of drought are only partially understood.
- They lie somewhere in the complex interactions between atmosphere, oceans, cryosphere, biosphere and the land, which produces the climates of the globe.
Meterological drought is a ….. deficit
rainfall
Agriclutural drought is a ……. deficit
soil moisture
Hydrological drought is a …… deficit
stream flow
socio-economic drought is a……… defict
food
Define hydrological drought
- low water supply in our irvers, lakes, aquifers, & other reservoirs that often follows meteorlogical drought
Define agricultural drought
- drought when a water shortage significantly damages or destroys agricultural crops
Define socio-economic drought
- dought refers to when a water shortage affects the supply & demand of drought commodities
- e.g water food, grains & fish
Define ecological drought
- the most recently defined type of drought
- refers to the widespread ecological damage caused by the lack of soil moisture
What are the features of hydrological drought
- Reduced infiltration
- Low soil moisture
- Little percolation and groundwater recharge
What are the features of agricultural drought
- Low evapotranspiration
- Reduced biomass
- Fall in groundwater level
What are the features of socio-economic drought
- Loss of vegetation
- Increased risk of wildfires
- Soil erosion
- desertification
What are the impacts of hydrological drought
- Reduced storage in lakes and reservoirs
- Less water for urban supply
- Poorer water quality
- Threats to wetlands and habitats
What are the impacts of agricultural drought
- Poor yields from rainfed crops
- Failing irrigation systems
- Livestock productivity falls
- Rural industries affected
- Government aid may be required
What are the impacts of socio-economic drought
- Widespread failure of agricultural systems
- Food shortages
- Rural economy collapses
- Rural to urban migration International aid required
- Humanitarian crisis
Water is ……. distributed …. across the globe
- spatially
- unevenly
…% of the world’s population live in areas which only have access to …% of the world’s annual rainfall
66% of the world’s population live in areas which only have access to 25% of the world’s annual rainfall
…..% of the worl’d land area has some level of drought exposure
38%
Causes of meteorological drought
Explain how global atmospheric circulation can cause meteorological drought
- Heat is greatest at the equator due to the concentration of the sun’s energy
- This causes air to rise (convection) at the equator (the driving force of the whole model)
- This air then cools and condenses creating rain (hence tropical rainforests at the equator)
- Air moves polewards, cools and sinks at around 30 degrees N and S of the equator creating subtropical high-pressure belts
- As air is sinking no clouds form and so these areas are dry (worlds major deserts)
Causes of meteorolgical drought
What is the ITCZ
- The Intertropical Convergence Zone, or ITCZ,
- is a band of low pressure around the Earth which generally lies near to the equator
- The trade winds of the northern and southern hemispheres come together here, which leads to the development of frequent thunderstorms and heavy rain
Causes of meteorolgical drought
What is the impact of season shifts in the ITCZ
- Seasonal shifts in the location of the ITCZ drastically affects rainfall in many equatorial nations,
- resulting in the wet and dry seasons of the tropics
- rather than the cold and warm seasons of higher latitudes
- Longer term changes in the ITCZ can result in severe droughts or flooding in nearby areas
Causes of meteorolgical drought
- Longer term changes in the ITCZ can result in……
- Longer term changes in the ITCZ can result in severe droughts or flooding in nearby areas
…% of the global population are vulnerable to severe drought
18%
What is the air pressure 90 degrees from the equator
high pressure - clear, sunnier weather
What is the air pressure 60 degrees from the equator
low pressure - rainy weather
What is the air pressure 30 degrees from the equator
high pressure - clear, sunnier weather
What is the air pressure at the equator
low pressure - rainy weather
The ITCZ moves ………. as the planet …….
When it moves it brings the monsoon to India, when it moves to South, India returns to…..
The ITCZ moves seasonally as the planet tilts
When it moves it brings the monsoon to India, when it moves South, India returns to drought conditions
What is blocked weather
- Usually, weather fronts (which bring rain) move from w to e across the UK,
- but sometimes they can staywhere they are, or even go from e to w, & this is usually due to a ‘block’
- This means a big area of high pressure is remaining almost stationary over the samearea for a long time
- The high pressure can stop weather fronts moving past it, so that they skirt around the edges, or stay where they are for an extended period
what is a blocking anti-cyclone
- the winds tend to be light & blow in a clockwise direction, the air is descending, which stops the formation of clouds
What is an example of a blocking anti-cyclone
- European heatwave where UK hit 40 degrees in 2021
What does ENSO stand for
- El Nino Southern Oscillation
What are the 2 events in ENSO
- El Nino
- La Nina
During El Niño, winds and ocean currents across the……, …….. direction.
This changes the weather patterns around the Pacific.
Occurs every ……….years, although they appear to be getting……..
- Pacific, change
- 3 – 7
- more regular
How long do El Nino events usually last
- 18 months ish
What are the conditions in the Pacific Basin in a normal year
- Trade Winds blow from east yo west along the equator
- This moves warm surface water towards the western Pacific
- cold water upwells up along the west coast of S. America (near Peru)
- Warm moist air rises, cools & condenses there forming rain clouds in the West
What is upwelling
- an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water from deep water
- towards the ocean surface,
- replacing the warmer, usually nutrient-depleted surface water
What are the conditions in the Pacific Ocean during El Nino
- Air pressure over West coast of S. America becomes low & air pressure over west Australia becomes high
- The normal east to west trade winds over Pacific are disrupted
- it may slacken or even reverse & this has a knock on effect on the ocean currents
- warm water ‘sloshes’ eastwards
- No upwelling on S. American coast
Describe the effect on water temperatures from El Nino
- 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
El Niño events seem to trigger ……….. conditions throughout the world, usually in the ……… year
For example,….
El Niño events seem to trigger very dry conditions throughout the world, usually in the second year
For example, the monsoon rains in India and South East Asia often fail.
Why is upwelling important for fish stocks in Peru
- With the movement of warm water back eastwards, it prevents any upwelling of cold nutrient-rich, water on which Plankton feed
- Plankton is the main food of the anchovy which is one of the main fishing types in Peru
- Warm water also expands,
- so as the water piles back East towards Peru sea levels increase by 30cm
Define thermocline
- The boundary in the ocean between warm surface water and cold deep water
What is La Nina
- Occasionally as an El Niño year dies out, a third weather condition arises: La Niña
- All it is, is an exaggerated version of normal conditions
Describe what happens in La Nina
- Air pressure is unusually high over the west coast of South America and low over eastern Australia
- As warm water is pushed westwards, sea levels rise by up to 1m
- Around Indonesia and Philippines, strong uplift of air (very strong air circulation) leads to heavy rain
La Nina can lead to ………, particularly on the ….. coast of …….. …….
La Nina can lead to severe drought conditions, particularly on the Western Coast of South America
List some of the anthropogenic causes of drought
- deforestation
- dam construction/ river diversion
- over abstraction
- poor agricultural practises -over grazing
- micro climate changes -urbanisation
- climate change
what is a microclimate
- tthe distinctive climate of a small-scale area e.g a park, garden or part of a city
- the weather varaibles in a microclimate, such as temp, rainfall, wind or humidity
- may be subtly different from the conditions prevailing over the area as a whole, varying from whats expected under certain types of pressure or cloud cover
Define desertification
- the process by which once-productive fertile land gradually changes into a desert-like landscape
- it usually takes place in semi-arid land on the edges of existing deserts
- it is not neccessarily irreversible
How does global warming lead to desertification
- increase in average climactic temperatures
- increased rate of evaporation of water moisture especially in tropical or sub-saharan climates
- if more moisture has evaporated, less will be available for convectional rainfall
- so plant growth will be stunted & vegetation dies
- leading to desertification
How does reduced precipitation lead to desertification
- changing rainfall patterns - less reilable, seasonally & annually
- the occassional drought year sometimes extends to several years
- as vegetation dies, the protective layer it provides for soil will also be removed
- soil is increasingly exposed to wind & rain
- accellerates soil erosion, as short intense rainfall makes it difficult for soil to capture & store it
- positive feedback loop of worsening soil conditions & vegetation death
- leading to desertification
Explain the human causes of desertfication which create a positive feedback loop
- population growth is the root cause of recent increase in rates of desertifcation
- demand for food, water & other resources also increases
- this leads to over cultivation & overgrazing (intense cattle farming), so intense use of marginal land exhausts soil
- also, deforestation via burning of trees exposes top soil to erosion, & worsens quality
What is the situation with the Sahel Drought, Africa 2011-12
- The northern Sahel region is experiencing a 30-40% annual departure from ormal rainfall
- things have been exacerbated by frequent civil war & unprescedented levls of organised violence in 2018 - food & livestock deliberately destroyed
Human factors act like a …………………. …………., humans enhance the impacts of drought by…
- feedback loop
- the overanstraction of surface water from rivers & ponds, & groundwater from aquifers
What are the impacts of the Sahel Drought
- 4.2 million displaced people
- protracted armed violence exacerbates the situation of food insecurity, malnutrition & epidemics
- farming & trade severely impaired
- high concentrations of herds in pastoral enclaves, & natural reserves where risks of epizootic diseases are high
- 9.7 million people vulnerable to food insecurity —> high malnutrition rates
Describe the responses to the Sahel Drought
- 5 wells rehabilitated
- redistribution of animals & agricultural kits
- vaccinating 500,000 animals
- BUT there is a funding gap of 73.5% - $122.6 million
What is the situation with the Australia Drought 1997-2009
- prone to drought as Ocenia spans the latitudes of the subtropical high pressure belt
- this means most the country’s rainfalll is low & erratic
- they experienced over a decade of below average rainfall, 30% affected by serious or severe rainfall deficiency
What were the consequences to Australias’ drought
- death of livestock
- 33 wetlands temporarily disconnected to help save water
- pipelines had to be built to deliver drinking water to lower lake communities
How has Australia’s drought been managed
- Unlike the Sahel, Australia has not followed the same downward spiral of desertification
- a careful management of scarce water resources, & sorting out the competing demands of irrigation & urban dwelllers has also stopped this happening
- also large scale recycling of grey water
- csonstructing desalination plants
- devising new water conservation strategies
Give an example of an issue with an Australian water conservation strategies
- Western Corridor Recycled Water Scheme
- faced community resistance as treated waste water will never be safe enough to drink
Define ecosystem functioning
- refers to the biological, chemical, and physical processes that take place within the ecosystem
Define ecosystem resilience
- the capacity of an ecosystem to respond to disturbance from it’s normal state by resisting damage and recovering quickly
What is the impact of drought on Forest Ecosystems
- Living trees take 2-4 years to recover and resume normal growth rates following a period of drought
- Long-term harm drought-stressed trees includes foliage loss, impairing growth, lasting damage to tissues within the tree impairing water transport —> increased susceptibility of pines & firs to fungal diseases
- Significant die-off of certain species e.g - Pinon pines —> can reduce carbon sequestration
What is the impact of drought on Wetland Ecosystems
- reduced interception causes vegetation to wilt & die
- this results in less soil nutrients, impacting rest of food web
- progressive loss of habitat as open water source shrinks, reducing soil moisture –> eroison
- some land species will be affected as the dry soil will be less penetrable, limiting their ability to get food
What is the value of Wetlands that has been discovered over the last 50 years
- Wetlands currently cover about 10% of the Earth’s land surface
- & until 50 years ago they were considered as wastelands, only good for draining and infilling to provide building land
- However, it is now understood that wetlands perform a number of important functions: from acting as temporary water stores to the recharging of aquifers, from giant filters trapping pollutants to providing nurseries for fish and feeding sites for migrating birds
Brazil Drought - Amazon Rainforest
In 2014, climate scientists reported that deforestation in the Amazon may now have…
- passed a tipping point - in other words, changing hydrological and climatic cycles permanently
Brazil Drought - Amazon Rainforest
What is the cause of drought in the Amazon Rainforest
- Rainforests recycle half of their rainfall, but the positive feedback loop of deforestation and less rainfall is reducing the ability of the rainforest to regenerate
- This makes fragile rainforest ecosystems less resilient
- Thinning forests have reduced soil water storage and evapotranspiration
- In turn, these lead to changing weather patterns - with lower precipitation
Brazil Drought - Amazon Rainforest
Why are tropical stores & fluxes really important
- forests regulate regional climate and generate flows of moisture across the continent
- Now, the combined risk of global climate change, ENSO cycles & deforestation will probably alter this so that extreme weather will become more frequent
Brazil Drought - Amazon Rainforest
What is the impact of drought
- the Amazon rainforest’s capacity to absorb carbon will decline
- regional water cycles will change and soil temperatures will increase
- the Amazon rainforest will be replaced with savannah-like grasslands
- more wildfires will increase the level of carbon in the atmosphere
- reduced rainfall will threaten Brazil’s dependency on HEP (which generates 70% of its electricity)
Where is flooding always a possibility
- Floods in areas experiencing meteorlogical conditions providing a lot of precipitation flooding
Flooding can occur as ………………. or as ………..
- fast onset ‘flashfloods’ or as slower onset hazards
When does the most common form of flooding occur
- when a river reaches & then exceeds bankful discharge,
- additional water cannot be contained within the channel
- & so spills onto the surrouding land,
- making the floodplains innundated with water
List the 5 meteorlogical causes of droughts
- Intense Storms
- Prolonged rainfall
- Heavy rainfall
- Snowmelt
- Monsson rains
Intense storns
For example, ………… bring a lot of rainfall in a realtively ………., often without …………
Tropical cyclones bring a lot of rainfall in a relatively short time period, often without warning
Intense storns
What happens when intense storns bring a lot of rainfall in a very short period of time
- water moves quickly into channels, as it is unable to soak into the ground causing them to overflow their banks
Intense storns
Where are flashfloods common
- arid
- semi-arid areas
- mountainous areas
Intense storns
What are flash floods
- In arid & semi-arid areas, occassional thunderstorms drop a lot of rain suddenly which runs quickly over the baked ground, creating ‘flash floods’
Flashfloods can be characterised by ………
- short lag-times
What causes prolonged rainfall
- persistent rain over a long period of tine, perhaps the result of several low pressure systems (depressions) passing over an area, causes a sequence of frontal rainfall
- In the UK, deep dpressions can cause this
Define depressions
- a system of low pressure, with fronts of precipitation where low & high pressure air masses meet
How does prolonged rainfall cause prolonged rainfall
- first the soil is saturated so that later rainfall cannot infiltrate
- runoff is increased & quickly enters river channels, causing floods
Heavy Rainfalll
- What causes heavy rainfall
- a cold front in a low pressure system can cause a lot of rain to fall over a short period of time
Heavy Rainfall
- how does heavy rainfall cause flooding
- intense rainfall in a short time period can be too much to allow throughflow or groundwater flow to take place,
- so the excess waterquickly runs off the surface & into the river channels where discharges increase to exceed flood levels
Snowmelt
1 . Where is winter snowfall highest
In some mountainous regions, winter snowfall accumulates to a considerable depth
Snowmelt
- ……. temperatures in Spring cause snow to…..
warmer
rapidly start melting
Snowmelt
- Describe the rapid snowmelt that can occur in spring in some mountainous regions
The groundwater under the snow may still be frozen so a lot of the melt water flows rapidly down steep sloped into river valleys, casuing increased river discharges
Where does snowmelt cause meterological flooding
- The plains of Siberia
Define monsoon
- The drastic variation between wet and dry seasons for sub-tropical
areas, caused by a changed prevailing wind - Can lead to annual flooding
Which areas get monsoon rain
- subtropical areas have a wet season, these are especially wet land areas between mountains & warmer oceans (e.g India)
How do monsson rains cause flooding
- Monsoon seasons are charaterised by torrential rainfall, which initially falls onto hard, dry ground –> increasing run off,
- & then onto staurated ground
- with the months of heavy rainfall adding to runoff & increasing river levels until they flood
What are flood data bases used for
- to analyse long-term trends
What is the EM-DAT database
- shows floods that appear to be increasing in frequency & severity largely due to climate change & increasingly popularity pressure e.g Central Europe
What is FLOPROS
- Flood Protection Standards Global Database
What is Flood Protection Standards Global Database
- assesses flood risk by analysing the links between the flood return period & flood protection measures
- it combines information on flood portection measures & policies within a modelling approach
- the data output does not take into account future change e.g climate or population
What is tidal fooding often the result of
- Often a result of storm surges or when high river flows meet particularly high spring tides in estuaries
What causes a storm surge
- caused by very low air pressure which raises the height of the hightide sea
- strong onshore winds then drive the raised sea towards the coast , often breeching coastal defences & flooding large areas
Which types of land areas are even more susceptible/vulnerable to surpluses in water
- low-lying land, the base of river valleys & estuaries
- urbanised, built environments
- small basins, esp in semi & arid areas
Why are low-lying land like the base of river valleys & estuaries more vulnerables to surpluses
- river flooding can occur along with groundwater flooding as the ground becomes saturated,
- therefore any surface close to the water table is vulnerable
Why are urbanised, built environments more vulnerables to surpluses
- impermeable surfaces increase surface runoff, reducing lagtime, so increasing the risk of flash flooding
Why are small basins more vulnerables to surpluses
- impermeable surfaces increase surface runoff, reducing lagtime, so increasing the risk of flash flooding
Explain how the likelihood of flooding is also enhanced by other physical circumstances
* geology
where ground surface is underlain by impermeable rocks
Explain how the likelihood of flooding is also enhanced by other physical circumstances
* sudden unusual melting
when ice dams suddenly melt & the water in glacial lakes are released
Explain how the likelihood of flooding is also enhanced by other physical circumstances
* volcanoes
- where volcanic activity generates meltwater beneath ice sheets that is suddenly released (jökulhlaup)
- —> a glacial outburst flood that occurs when a lake fed by glacial meltwater breaks through its dam and drains rapidly
Explain how the likelihood of flooding is also enhanced by other physical circumstances
* seismic activity
where earthquakes cause the failure of dams & landlsides that block users
Bangladesh is a particularly food-prone country mainly because…..
- it is a land of floodplains and deltas built up by mighty rivers such as the Ganges, Padma and Meghna
Bangladesh
The Ganges, Padma and Meghna are swollen …… a year by….
twice a year
meltwater from the Himalayas, and by the summer monsoon
Bangladesh
……. between the rivers and behind Chittagong are often victims of …………
- Hilly tracts
- flash floods
In what time period was there particularly bad flooding in the UK
- 2015/16 Winter Storm Season
Where was the 2015/16 Winter Storm season in the UK really bad
- North England, in particular, Cumbria, Scotland, Northern Ireland
2015/16 Storm Season
Where did record peak flows occur in the UK
- River Tynes & Eden in Scotland
- Clyde & Tay in Scotland
2015/16 Storm Season
Large areas of the UK recorded ………
more than double the average amount of rainfall
What were the causes of the UK flooding 2015/16
-human causes
- budget cuts on the amount of spending on flood defences
- poor land management –> blocked ditches
- global warming
What were the causes of the UK flooding 2015/16
-physical
- low pressure weather systems, brought by the Jet Stream
- prolonged heavy rainfall - orographc & convectional
What were the causes of the UK flooding 2015/16
-international interferences
- An EU directive that puts environmental conservation ahead of the regular dredging of rivers changed the sedient flux balance durastically
What is realised by post-flood enquiries
- flood protection methods are designed to cope with flood events of a given magnitude
- when an event of very rare magnitue occurs, no amount of money or engineering is going to prevent the hoped degree of protection
UK 2015/16 storm season
- Storm Abigail was caused by
- excessively saturated soils in early November
UK 2015/16 storm season
What made flooding by Storm Desmond so bad
- In Cunbria, over 1 months rainfall came in one day (convectional & orographic rainfall was combined with frontal rain)
UK 2015/16 storm season
how many properties were damaged
- 16,000
UK 2015/16 storm season
how much compensation did the UK govt provide
- £200 million
UK 2015/16 storm season
Estimated total costs?
- £5 billion
UK 2015/16 storm season
Economic consequences?
- businesses damaged
- insurance costs
- emergency crises
- consumers & deliveries unable to reach businesses
UK 2015/16 storm season
Infrastructure costs?
- roads & railways blocked
- healthcare disruptions
- power cuts
- schools closed
UK 2015/16 storm season
Costs to settlements?
- property damaged
- people evacuated
- sediment deposited in houses
Give 4 examples of positive environmental impacts of flooding
- recharged groundwater stores
- increased connectivity between aquatic habitats - triggering larger migration, dispersal & breeding events
- soil replenishment by the movement of sediment
Elaborate on the positive impact on soils of flooding
- soils may become waterlogged on level ground or scoured away on sloped by increased surface flow
- flood events reduce the microbial biomass in soil, but in th elong-term more nutrient rich sediments, esepcially on floodplains are provided
Explain how most ecosystems can cope with flooding
- Most ecosystems have a degree of ecological resilience that can cope with the effects of moderate flooding
- small floods can replenish water levels creating wetland habitats & replenishing long-term nutrients
Yet there is an extent to which floods are beneficial to ecosystems…
- It is where the environment has been degraded human activities that negative impacts are more evident (extreme floods & degredation)
the removal of soil and sediment by floodwaters can lead to the ……………of water bodies
- eutrophication
That same floodwater can also……………………. with disastrous effects for ……………………….., while …………….. carried by floodwater can weaken or kill trees, which in turn means…..
- leach pollutants into water courses
- aquatic wildlife & ecosystems
- diseases
- plant biomass & invertebraes are reduced
What other forms of pollution during meteorlogical floods can harm aqautic ecosystems
- nitrates, chemicals & heavy metals
Th degree of threat posed by floods depends on…
- the depth & velocity of the water
- e.g wtaer 0.5m deep can wash cars away & cause building foundations to collapse
Describe how human actions can increase flood risk
Floodplain use
- population pressures & rural-urban migration increase building on floodplains
- depite flood protection methods, major floods can still occur
Describe how human actions can increase flood risk
Land use change
removal of natural vegetation, especially deforestation, changes hydrological processes in th catchment area
increased soil erosion adds sediment to river channels, changing the basin shape & reducing the capacity, so floods can occur with a lower discharge
What are examples of land use change that increase flood risk
- impermeable areas of tarmac, sprinkling of groundwater onto arable crops
- streams channellled into currents to aid rapid drainage of farmalbd
- ploughing & grazing compacts soil
Describe how human actions can increase flood risk
River management - channelisation
- an effective way of improving river discharge & reducing floodrisk
- but simply displaces the river flow downstream, overwhelming these locations during peak discharge
Describe how human actions can increase flood risk
River management - dams
- dams block the flow of sediment down a river, so the reservoir graduallly fills up with silt; downstream there is increased river bed erosion
Describe how human actions can increase flood risk
River management - embankments
- embankments are built to improve bankful capacity,
- using concrete or sustainable materials (usually dredged from the channel)
- however, if these are breached the scale of flooding is far greater
