How can weather be hazardous?

• Global circulation system

  • winds carry heat from warmer low latitudes to cooler high latitudes and back again through a system of looped cells either side of the equator.
  • high pressure is caused by hot air sinking which causes clear and calm weather.
  • low pressure is caused by hot air rising which causes stormy and cloudy weather.

  
• The three-cell wind model

  • these cells circulate air from the surface up to the high atmosphere and back down to Earth's surface.
  • Hadley cell, largest cell that starts at the equator and reaches between 30 and 40 degrees north and south.
  • Polar cell, smallest and weakest cell that reaches from the edge of the Ferrel cell to the poles at 90 degrees north and south.
  • Ferrel cell, in the middle at the edge of Hadley cell between 60 and 70 degrees north and south of the equator.

  
• Surface winds

  • trade winds, blow from subtropical high-pressure belts towards the equator's low-pressure zones, deflected by Coriolis force.
  • westerlies, blow from subtropical high-pressure belts to the mid-latitude low areas, deflected by Coriolis force.
  • easterlies, polar easterlies meet the westerlies at 60 degrees south.
• Coriolis effect

  • the appearance that global winds and ocean currents curve as they move, due to the Earth's rotation on its axis
  • northern hemisphere, winds curve to the right.
  • southern hemisphere, winds curve to the left.
  • low pressure system, winds flow in reverse.
• Global circulation

  • global atmospheric circulation affects the Earth's climate.
  • the UK has a lot of low-pressure weather systems, that blow in from the Atlantic Ocean on south-westerly winds, bringing wet and windy weather.
  • UK is classified as a temperate weather system, no extremes of weather.
  • the lower the pressure system the higher and stronger the winds become.
• High pressure zones

  • created, air descends exerting pressure on the Earth's surface.
  • climatic conditions, air is stable, clear and dry, winds are light and low.
  • Arid, 30 degrees north and south of the equator, high or low temperature with little to no precipitation.
  • Polar, 90 degrees north and south with low temperatures, little to no precipitation.
• Low pressure zones

  • created, air rises releasing pressure on the Earth's surface.
  • climatic conditions, air is unstable, cloudy and wet with thunderstorms, winds are strong and high.
  • Tropical, 0 degrees equatorial region with high levels of rainfall, high temperatures and humidity.
  • Temperate, 60 degrees north and south of the equator, moderate weather but can experience extremes of dry or wet weather occasionally.
• Extreme weather conditions

  • winds, relatively weak within pressure zones, between the pressure zones the winds are strong, the larger the pressure difference the stronger the winds.
  • precipitation, occurs when warm, moist air rises, cools and condenses, in low pressure areas there is frequent precipitation, in high pressure zones there's little precipitation.
  • temperature, the Equator recieves the highest level of sunlight, warmest and wettest areas.
• UK compared to Australia

  • temperature, cooler, in London the average maximum summer temperature is 23 degrees.
  • precipitation, higher, average annual rainfall is 1150mm.
  • wind, gales over 62km/h are rare, most places in the UK only have a few days of gales each year.
• Australia compared to the UK

  • temperature, warmer by about 10 degrees, the average maximum summer temperature is 33 degrees.
  • precipitation, lower, average annual rainfall is 465mm.
  • wind, stronger extreme winds, affected by tropical cyclones with winds over 118km/h.
• Tropical storms

  • distribution of tropical storms is consistent, however their frequency varies.
  • they are rotating, intense low-pressure systems.
  • typhoons, South China Sea and west Pacific Ocean.
  • Hurricanes, Gulf of Mexico, Caribbean Sea and west coast of Mexico.
  • Cyclones, Bay of Bengal, Indian Ocean and Northern Australia.
• Distribution of tropical storms

  • they develop over the warm tropical oceans between 5 and 15 degrees north and south of the equator.
  • ocean temperatures must be 26.5 degrees or higher and have a depth of 60m.

  
• Frequency of tropical storms

  • an average of over 80 tropical storms are generates by tropical oceans every year.
  • usually in late summer.
  • the Pacific Ocean sees the largest number of tropical storms, with the storms in the western Pacific being the strongest.
• Changes in frequency

  • the number of Atlantic storms has increased but the overall global frequency remains steady.
  • the intensity of tropical storms has increased by 70% over the last 30 years.
• Droughts

  • extended period of time when there is below average rainfall.
  • negative effect on vegetation, animals and people.
  • droughts are often accompanied by high temperatures, increases the rate of evaporation, depleting water supplies faster.
• Causes of drought

  • changes in atmospheric circulation can reduce the amount of precipitation to an area.
  • high pressure weather systems bring high temperatures which increases evaporation rates, but also block weather depressions of rain bearing clouds.
• Frequency and distribution of droughts

  • frequency of droughts hasn't changes the distribution has.
  • areas most at risk are Australia, Middle East, central and southern Africa.
  • most areas affected by drought already fringe desert regions and are at risk of longer drought situations.
  • drought may become more frequent and more severe in the future with global warming.
• Causes of tropical storms

  • causes are related to the Hadley cell, the Coriolis effect and equatorial trade winds.
  • equatorial regions receive intense solar heating raising ocean temperatures.
  • the warm, moist air rises, leading to intense low pressure zone's.
  • this generates thunderstorms, strong winds and intense rainfall.
  • the greater the low pressure the greater the winds the greater the spin and the larger the tropical storm becomes.
• Relationship between atmosphere and tropical storms

  • sea temperatures must be 26.5 degrees Celsius, allowing warm air to rise causing an area of intense low pressure.
  • they form between 5 and 30 degrees north and south of the equator.
  • rising air draws further moist, warm air from the ocean's surface, generating stronger winds.
  • the air spirals upwards, cools, condenses and forms large clouds.
  • these clouds produce heavy rainfall.
  • cold air sinks at the centre, creating a calm, dry area called the eye of the storm.

  
• Causes of El Nino and La Nina

  • they are climatic events in the Pacific Ocean.
  • the ENSO cycle is the change in the movement of warm water mass in the equatorial region of the Pacific Ocean.
  • happens due to changes between trade winds, atmospheric circulation and ocean currents.
• Causes of El Nino

  • in a normal year air descends over the eastern Pacific, with rising, warm moist air over the western Pacific.
  • this event occurs when sea temperatures reach 0.5 degrees Celsius above average.
  • the low level easterly trade winds weaken.

  
• Effects of El Nino

  • reduction or reversal of the winds lead to warmer than average weather in central and eastern Pacific.
  • precipitation reduces over Indonesia, increases over the tropical Pacific Ocean.
  • the peak is usually in December and occurs every 2-7 years.
  • ocean temperature off the coast of Peru rises by 6-8 degrees Celsius causing thermal expansion and sea level rise of 30cm, rising air and low pressure producing more precipitation than normal.
  • water off the coast of Australia is cooler, precipitation is reduced, high pressure and stable, dry or drought conditions in Australia.
• Causes of La Nina

  • occurs when sea temperatures fall below average.
  • brings cooler and drier than average weather in the eastern Pacific.
  • occurs every 3-5 years to counteract El Nino.
• Effects of La Nina

  • stronger than usual easterly trade winds and ocean currents.
  • increased precipitation over Indonesia and decreasing rainfall over central tropical Pacific Ocean.
  • cold water is brought to the ocean surface through upwelling.
  • they both impact global climate due to the changes they cause in the high atmosphere.

  
• Impacts of both El Nino and La Nina

  • El Nino has the most significant impacts with increased rainfall and flooding in South America and Africa and the south of the US, drought in Australia and Southeast Asia, linked to a higher risk of colder winters in the UK.
  • La Nina leads to increased rainfall in Australia and Southeast Asia, drought conditions in the south of the US, increased risk of tropical storms in the Atlantic.
• Case study UK heatwave

  • the heat wave of August 2018 became one of the hottest years since records began in 1960, reaching the temperatures of 38.5 degrees Celsius in some parts of the UK.
• Cause of 2018 heat wave

  • in June and July an anticyclone which is a high pressure system, sat over the UK bringing dry, hot air from the centre of Europe.
  • this kept the UK temperatures higher than usual and lowered precipitation rates, 47mm of rain fell in those months.
  • any low pressure systems of cool air and rain from the Atlantic Ocean were blocked by the anticyclone.
• Consequences of the heatwave

  • heat stroke, dehydration, sunburn, and breathing problems caused by air pollution.
  • 2000 heat wave linked deaths in the UK.
  • wildfires were common due to the dry conditions and large areas of national parks were affected.
  • water supplies were threatened as water levels dropped in reservoirs.
  • loss of livestock and crops due to lack of water availability.
  • food and drink production was increased and ice-cream sales tripled.
  • tourism in the UK increased as many people decided to holiday at home.
• Responses to the heatwave

  • guidance issued by the government and NHS on how to deal with the heat by keeping hydrated, take cool showers, block out sunlight to keep rooms cool.
  • hose pipe bans were put in place in parts of the UK and restrictions were put in place on water usage.
  • farmers allowed to extract more water to help avoid loss of crops and livestock.
  • some rails painted white to reflect heat to prevent buckling and some trains were cancelled.
• Case study typhoon Haiyan 2013

  • was one of the strongest ever-recorded tropical storm to hit the Philippines.
  • made landfall on the 8th of November 2013 and was a category 5 with sustained winds over 195 mph.
  • Philippines are a series of islands located in the South China Sea, and regularly suffer from typhoons that sweep in from the southwest every year during the tropical storm season.
  • the islands sit in an area of usually warm ocean water, but at the time the sea temperature was 30 degrees Celsius.

  
• Typhoon Haiyan characteristics

  • lowest pressure was 895mb.
  • peak strength was category 5.
  • strength at landfall was category 5 with 195 mph winds.
  • highest sustained wind speed 195 mph.
  • radius of typhoon strength winds was 53 miles.
  • rainfall was 400mm.
  • storm surge height was 5-6m.
• Impacts of typhoon Haiyan

  • total economic loss was $13 billion.
  • homes damaged or destroyed was 1.1 million.
  • displaced people was 4 million.
  • number of deaths was 6200.
  • number of missing people was 1700.
  • number of injured people was 28,600.
  • number of people affected was 16 million.
• Social impacts of typhoon Haiyan

  • short term, UN admitted its response was too slow, amid reports of hunger and thirst among survivors, 28,600 casualties due to lack of aid.
  • long term, UN feared possibility of spread of disease, lack of food, water, shelter and medication, areas less affected has an influx of refugees, two months later 21,000 families were still in 380 evacuation centres waiting to be rehoused by the government.
• Economic impacts of typhoon Haiyan

  • short term, major sugar and rice production areas were destroyed so between 50,000-120,000 tonnes of sugar was lost and 130,000 tonnes of rice were lost, the government estimates that 175,000 acres of farmland was damaged worth $85 million.
  • long term, Philippines asked for international help, the president under going pressure to speed up the distribution of food and medicine, the Tacloban city was decimated, debt is a major obstacle for them with the country locked in a debt cycle with more than 20% of government revenue spent on foreign debt repayments.
• Environmental impacts of typhoon Haiyan

  • short term, loss of forest and widespread flooding, oil and sewage leaks into ecosystems, lack of sanitation in days following leading to higher level of pollution, fishing communities were severely affected.
  • long term, 90% of rural population in typhoon affected areas are small scale farmers, without crops the families would not have cash to enable local markets to function.
• Short term responses to typhoon Haiyan

  • international aid agencies responded quickly with food water and temporary shelters.
  • Philippines Red Cross delivered basic food like rice and canned food.
  • UK sent shelter kits to provide emergency shelter for a family.
  • 1200 evacuation centres set up for the homeless.
  • $475 million sent as aid and US sent 13,000 soldiers.
• Long term responses to typhoon Haiyan

  • UN donated financial aid, supplies and medical support.
  • 5 says went before any aid was received and only 20% of victims received aid.
  • UN admitted its response was too slow.
  • rebuilding of the airport, ports, roads and bridges.
  • cash for work schemes gave locals money to help clear the debris.
  • Oxfam helped finance replacement of the fishing boats.
  • increased number of cyclone shelters have been built further away from coastal areas.