Geography - Weather hazards

how does global atmospheric circulation work?

- Air rises at the equator up to 15km due to the sun's heat, leading to low pressure area.

- It travels both North and South

- The air becomes colder and denser, and falls, creating high pressure and dry conditions at around 30° north and south of the equator.

- Large cells of air are created in this way. The Hadley cell is either side of the equator, ferrel cells on either side of them and the polar cells at the poles. Both Hadley and Polar cells flow the same way and are driven by temperature whilst Ferrel cells just distribute the air.

- at 30°, the cool air either moves back as trade winds to equator or as westerlies to the poles.

- Air rises again at around 60° north and south as the winds heat up at the surface and rise again, descending again around 90° north and south once this energy is lost

- the Coriolis effect causes the winds to become curved

what do ocean currents do?

• Ocean currents also transfer heat.
o Oceans transfer approximately 20 per cent of the total heat from the tropics to the poles. o They are produced as massess of water move from one climate zone to another.
o The are created by surface winds generated by global atmospheric circulation

why is the weather clear when there is high pressure and stormy at low?

HP: air sinks therefore leading to no cloud formation and clear skies. (subtropical/ polar climates)
LP: air rises therefore leading for it to condense into clouds and rain. (tropical/ temperate)

Why are there different climates around the world?

1) radiation from sun differs across the world
- the curvature causes equator to have more concentrated rays
- equator receives more heat as less atmosphere for rays to travel through to receive it,
- the tilt of the earth means some areas of polar regions don't receive any sun rays in the winter

2) the pressure system
- high pressure areas like at 30 degrees tend to have deserts as they have dry weather.
- low pressure (like on the equator having rainforests) have lots of rain

3) albedo effect, whiter areas reflecting sun rays

what conditions are needed for tropical storms to form?

- 27 degrees sea temp

- sea depth of 60-70m

- wind speeds over 74mph

- low wind shear to sustain clouds (low wind speed difference).

- Coriolis effect for spin

tropical storm names in different places:

hurricanes (atlantic ocean)
typhoon (north of the west pacific ocean)
cyclone (indian ocean/ around australia)

What is the GAC, pressure belts and surface winds?

- pressure belts are the bands of high and low pressure that move based of seasonal shifts, since the earth is on a tilt/ rotates
- winter: moves south
- summer: moves north

- surface winds are the winds of earth's surface that shift from high to low pressure to distribute heat. In northern hemisphere, they move to the right and southern to the left. They are curved due to earth's spin.

- the global atmospheric circulation refers to the way air circulates around the globe to distribute heat and how it creates pressure bands between circulation cells which influence the world's weather.

examples of how the GAC affects weather?

• GAC affects weather - examples

o UK (55°N) - cloudy & wet
▪ Boundary of cold polar air from north & warm tropical air from south
▪ Rising air means low pressure (Polar & Ferrel cells) - rain
▪ Surface winds from SW, warm & wet from Atlantic or N - snow from poles

o Deserts (5-30°N & S) - hot & dry
High pressure, air sinking - little to no cloud formation
- high sun concentration

o Equator (between 5°N & 5°S)- hot & wet
▪ Low pressure, air rising
▪ Hot due to direct sunlight at equator, humid due to cloud formation as air rises

what is a tropical storm and what are jet streams?

A tropical storm is a very powerful low-pressure weather system which results in strong winds (over 160 km/h) and heavy rainfall (up to 250 mm in one day), which can be classified into Saffir Simpson Scale depending on speed, pressure and damage potential

- jet streams are high-altitude streams of wind that divide the climate zones into their own areas (e.g. the polar jet/ subtropical jet). They are found between circulation cells.

how do tropical storms form?

- Air rises due to the heat.
- This air evaporates, cools and condenses into clouds which releases energy for the storm

- this rising air creates low pressure, causing more surface winds to be drawn in and upwards (along with more moisture) creating strong windy conditions

- these winds spiral upwards at 74mph to be classified as a storm. they then curve and condense outwards (due to convection) to form cumulonimbus clouds that create the eyewall. the heat given off here powers the storm. (as the clouds cool) --> eventually, these clouds characterized as having rapidly rising air
- many smaller thunderstorms combine together at this stage

- storm becomes cyclonic where it spins so fast to create a vortex, the centre of the storm which is made of cool descending air and has warm, calm and dry conditions.

- spins due to Coriolis force and is sent to the west by easterly winds. The low wind shear keeps storm in tact

- the storm gathers strength as it is carried across the ocean by the prevailing wind
- causes coastal flooding due to creating "domes" of seawater, forming storm surges

- upon reaching land the storm's energy supply (hot water) is cut off.
friction slows it down and it begins to weaken

Where do tropical storms form and why?

- 5-15 degrees north and south of the equator
- they don't form on the equator as coriolis force cannot be felt here
- they form close to it as sea is hottest there due to sun radiation
- low pressure system there meaning air rises to create clouds.

what is the structure of a tropical storm?

1)up to 240-320km across across

2)central eye (50km) is a small area where relatively cold air sinks toward the ground and warms up. no clouds and conditions are calm with no rain/ high temps

3)on either side of the eye is a tall bank of clouds called the eyewall. strong rapidly rising winds up to 160km/h, torrential rain, thunder, storm clouds and lightning

4)beyond eyewall there is further banks of clouds/ rain which have mild conditions with slight rain and quite windy.

- clouds arranged in a circular pattern, getting more patchier outwards and less dense outwards
- 13km high

- last 7-14 days
North: spin anti-clockwise - June-Nov
South: spin clockwise - Nov-April

What would a "weather forecast" for a storm be?

• "Weather forecast"
o Pressure & temperature rises. Wind/ gentle showers
o (wall) Torrential rain, strong winds, thunder & lighting, pressure & temperature rises
o (eye) calm, dry, no clouds, temperature rises
o (wall) fall in pressure, torrential rain, strong winds, thunder & lighting, temperature drops
o Temperature & pressure fall, gentle winds, showers
o Storm over

how will climate change affect tropical storms?

distribution, frequency, intensity

how will tropical storms become more distributed?

- more areas of the ocean becoming 27 degrees as worldly temps rise meaning that new latitudes will experience storms too.

- Hurricane Catrina, 2004
▪ SE of Brazil, first ever hurricane here

how will tropical storms become more frequent?

- oceans will stay at 27 degrees or higher for longer in the year, so there is a longer time period in which tropical storms can develop

- 6/10 most active years since 1950 were all after 1990s

how will tropical storms become more intense?

higher temps = more evaporation of clouds = more power for the storm

e.g. During last 25 years water vapour in atmosphere increased by 4% - making storms wetter

Give a summary of the Typhoon Haiyan case study:

- 8th November 2013
- 275 mph winds
- Category 5 of saffir Simpson scale
- 15m high storm surge (water that is pushed up by the storm's winds onto land, the low atmospheric pressure increasing it's height as it rises and collapses onto land).
- Tacloban/ Cebu were worst affected.

summary Haiyan primary effects

- 6300 killed
- 600,000 displaced and 40,000 homes destroyed
- 90% of Tacloban city was destroyed
- Tacloban airport destroyed
- 30,000 fishing boats destroyed
- 650,000 hectares of farmland destroyed
- 400mm of rain floodings.

KDHAFS
Kids Don't Have Any Fun Snails
Killed, Displaced, Homes, Airport, Fishing boats, Storm surge

summary Haiyan secondary effects

- 14 million were affected by damage

- 6 million lost their only source of income - due to damage to business and agricultural land destroyed

- Agricultural land destroyed would have led to food shortages as less food produced and therefore rising prices - leading to potential famine. (2014 -> 11.9% price increase for rice)

- Power supply cut of due to damage to connections (for a month).

- Food/ water/ shelter shortages = social impacts

- Looting and violence because of these shortages.

- Aid was disrupted by landslides - cut off roads and villages. (soil erosion) - socially impacting as they would have lacked resources, leading to more risk of death.

- Diseases such as dysentery spread due to lack of clean water (contaminated = arguably a primary effect but also secondary as a result of storm surge).

summary Haiyan immediate responses

- 1200 evacuation centres set up

- PAGASA having 800,000 residents evacuate after sending out warnings before storm, yet many died due to the floodings.

- Plan International constructed 100,000 pit latrines to prevent disease spread

- UK government sent shelter kits

- France, Belgium and Israel sent field hospitals

- Philippines Red Cross supplied over 1.1 million people with clean water

summary Haiyan long term resonses

- Long term aid such as financial - UN appealed for 300 million dollars.

- Programs for the citizens to clean up the city - which they were compensated for (helping those who lost their income). "cast for work"

- Charities such as Oxfam helped by replanting trees (Coconut trees only taking 5 years to grow).

- Oxfam helped re-establish some farming/ fishing industries with funding and replanting coconut trees to help add nutrients to the soil
- however it can be argued that with farming, Philippines being a large exporter of pineapples, this would take a long time to pick back up again with current contaminated soil (5 years for trees to grow and add nutrients).

- Charities helped cyclone shelters to be built.

- Rescue simulations to practice rescuing people for future storms.

how can the effects of tropical storms be reduced?

Monitoring , Prediction, Protection, Planning

Monitoring

- satellite images providing data on cloud cover/ formations
- radar satellite enabling tropical storms to be scanned for rainfall to forecast intensity.
- these predictions help calculate a path for the storm.
In North Atlantic 2 warning levels (prediction)
▪ Hurricane Watch - hurricane conditions possible
▪ Hurricane Warning - hurricane conditions expected, people should take shelter
o LICs are often less prepared because monitoring equipment is expensive and they may not have the ability to communicate information to people likely to be affected

- storm centres can issue warnings such as the national hurricane centre in Miami.
- e.g. cyclone phaillin in india was successfully predicted, causing 1.2 mil to evacuate (21 people died)

Protection - what are some strategies of protection?

- windows, doors and roofs reinforced to strengthen buildings to withstand strong winds

- storm drains in urban areas to take away excessive amounts of rainfall and prevent flooding

-flood defences built to protect key properties from storm surges

- houses close to coast constructed on stilts so that a storm surge will pass underneath/ houses having metal shutters to prevent debris from flying inside.

- in Philippines, mangrove forests act as natural flood defense.

How can planning reduce the effects of tropical storms?

- evacuation plans, having enough water to last if services get cut off

- future housing development not on high risk land, such as low-lying coasts

- evacuation routes/ emergency rations in case of being housebound for several days following a storm

- charities like red cross giving advice on what to do in a storm situation/ . Hurricane Preparedness Week - in the USA

- Philippines having rescue simulations to prepare for another storm after typhoon Haiyan.

what can strong winds damage?

destroy weak housing and can disrupt transport.
can also uproot trees and debris can injure or kill people. fallen trees can also cause road/ rail disruption such as in 2014, Clifton suspension bridge closure.

example of strong winds in the UK?

Storm Ali killed two people when 100mph winds blew over several trees

what effects does heavy rainfall have in the UK?

too much rain can cause flooding, which can damage homes, disrupt transport networks and drown people.
- recovering from flooding can cost millions of pounds

what is an example of heavy rainfall?

2014 somerset

what effects can snow and ice have in the UK?

- can cause injuries due to slipping and deaths due to cold
- schools and businesses can be forced to shut, and disruption to travel can have economic impacts

example of snow and ice:

March 2018, Beast from the East, brought up 50cm of snow, causing major disruption to traffic and schools

what effects can drought have in the UK?

- water supplies can run low, causing economic impacts such as crop failures
- hazardous to health
- rules to conserve water have to be introduced creating social unrest

example of drought in UK:

20,000 people died in the 2003 drought in Europe

what effects can thunderstorms in the UK have:

- heavy rain, strong winds and lightning can all occur
- lightning can cause fires, which can damage property and the environment and can occasionally kill people

example of a thunderstorm:

in July 2014, a series of thunderstorms struck southern and central England, with lightning strikes causing power cuts and delaying flights

what effects can heat waves have in the UK?

- during long periods of hot weather, pollution builds up in the air. this can cause heat exhaustion or breathing difficulties
- rails buckling/ roads melting have economic impacts for people's work however tourism industry may benefit

e.g. 2018 was one of the hottest summers since records began = 35 degrees in Kent.

What evidence is there for UK weather becoming more extreme?

• UK weather records broken since 2000:
o 2003, hottest temperature -> 38.5°C (Kent)
o 2009, record rainfall in November -> Lake District
o 2010, lowest temperature -> -18.7°C (Northern Ireland)
o 2013/14, wettest winter in 250 years o Dec. 2015, warmest & wettest December
o 2019, hottest temperature -> 38.7°C (Cambridge)

• Rainfall has increased 17% in the last decade
o The intensity has also increased e.g. a case 100mm in 3 hours (equal to 2 weeks average)

Why is weather becoming more extreme?

o Climate change - not the cause of single events but there is a trend over the past few years
- more energy (heat) in the oceans, leading to more intense storms
- more evaporation of water, leading to heavy rainfall
- colder temps come from --> glaciers melting --> colder water --> weakening of the gulf stream. +++ warming of arctic --> disruption of polar vortex due to differences in temp increased --> meandering jet stream, causing cold winters to reach lower latitudes
- droughts caused with warmer temperatures
▪ Atmospheric circulation affected with more heat, bringing floods to normally dry areas & heatwaves to cooler regions
▪ 2011, Intergovernmental Panel on Climate Change, concluded extreme weather frequency will increase due to global warming

o Weather patterns getting 'stuck'
▪ Weather systems W -> E in UK due to wind from 'jet streams'
▪ Jet steams move N -> S but can get stuck in one position, resulting in long period of the same type of weather causing floods or droughts
▪ Periods of stuck weather patterns, are becoming more frequent - likely due to climate change
▪ A warming Arctic may slow down atmospheric circulation in the northern hemisphere which may cause weather patterns to get stuck for longer periods

where are the Somerset Levels?

South West England - area of low lying farmland and wet land bordered by the Bristol Channel and Quantock Hills to the west and Mendip hills to the east

- from dec 2013 to feb 2014, major flooding occurred

what caused the floods in the Somerset Levels in 2014?

- wettest January since record began in 1910. a succession of depressions brought a period of wet weather lasting several weeks. about 350mm of rain fell in Jan and Feb, about 100mm above average.

- the area was already low lying therefore more susceptible to floods. --> human error to build there in the first place

- High tides: seawater levels were higher due to the high tides and storm surges that occurred with the heavy rainfall (the Atlantic depressions). This prevented the draining of water into the sea and only made the river levels further rise because of this lack in draining.

- though has many rivers, they had not been dredged for at least 20 years, and had become clogged with sediment

What were the economic impacts of the floods?

Economic:
- People lost jobs as they couldn't go to work (businesses closed) and lost farmland.
- Cost of damage was £10 million.
- Local companies lost £1.2 million.
- Tourism had to close - losing £200 million for the county.
- 14000 hectares flooded for 3-4 weeks

What were the social impacts of the floods?

Social:
- 600 homes flooded.
- Schools and businesses had to be shut, livelihoods disrupted
- Power supplies was cut off, reducing standard of living
- Villages such as Moorland were cut off and people were left stranded and affected daily lives such as shopping/ travel.
- Bristol to Taunton railway shut, disrupting routines.

What were the environmental impacts of the floods?

Environmental:
- 14000 hectares of farmland destroyed and 1000 livestock evacuated
- Standing water made ground unproductive and toxic - loss in fertility.
- Much vegetation damage (debris).
- ecosystems disrupted as habitats would've been destroyed

What were the management strategies in response to Somerset?

IMMEDIATE:
- warnings set out by Environment agency and warnings broadcasted by Met Office to evacuate before floods
- villages cut off used boats to shop/ attend school with community/ volunteer support
- temporary flood defences such as sand bags to protect homes/ businesses

LONG-TERM: 20-year action plan = Somerset and Moors flood action Plan
- Regular dredging of rivers parrett and tone (initial 8km dredging)
- Replacing temporary with permanent pumping systems to prevent flooding.
- Roads have been raised in some areas to reduce flooding risk and enable travel during floods.
- Establish authority (Somerset river authority) whom are responsible for effective river management.
- Tidal barrage at Bridgewater to stop high tides from contributing with floods.

What are some general impacts/ management strategies for UK weather events

ENVIRONMENTAL
- contamination of water supplies --> damage to ecosystems, drinking hazard
- air pollution (heatwaves)
- damage to crops/ farmland (snow/ ice or flooding)
- erosion from heavy rain
- landslides from heavy rain

SOCIAL
- deaths/ evacuations
- homeless/ stranded
- stress
- disruption to transport/ routine
- health at risk with lack of sanitation with floods

ECONOMIC:
- damage repair costs for country
- business/ industry (e.g. tourism) loss
- energy price risen (high demand for heating during clod weather)
- insurance costs to replace people's homes

MANAGEMENT:
- Environment agency = organises warnings/ evacuations
- flood defences to protect
- UK weather forecasters to identify weather threats

Difference between weather and climate?

Weather - day-to-day atmospheric conditions e.g. temperature, cloud coverage wind & rain Climate - an average of weather over a long period e.g. data taken from over 30 years

Why does the UK experience extreme weather?

o The UK is in the middle of multiple types of weather coming from different directions
▪ Arctic air can bring heavy snow & cold conditions
▪ Severe winter weather can come from the east
▪ Storms from the Atlantic bring heavy rain & strong winds
▪ Hot & sunny weather from the south can lead to heatwaves & droughts

UK is between 5 different air masses.