Extreme weather

From Wikipedia, the free encyclopedia https://en.wikipedia.org/wiki/Extreme_weather  Extreme weather or extreme climate events includes unexpected, unusual, severe, or unseasonal weather; weather at the extremes of the historical distribution—the range that has been seen in the past. Often, extreme events are based on a location's recorded weather history and defined as lying in the most unusual ten percent. There is evidence to suggest that climate change is increasing the periodicity and intensity of some extreme weather events. Confidence in the attribution of extreme weather and other events to anthropogenic climate change is highest in changes in frequency or magnitude of extreme heat and cold events with some confidence in increases in heavy precipitation and increases in intensity of droughts. Extreme weather has significant impacts on human society as well as natural ecosystems. For example, a global insurer Munich Re estimates that natural disasters cause more than $90 billion global direct losses in 2015.

Typhoon Haiyan, a massive tropical cyclone that struck the Philippines in late 2013.

 

A tornado in Binger, Oklahoma during the 1981 outbreak.

 

Trees felled by downbursts in the Boundary Waters – Canadian derecho of 1999.

 

Snow storm in New York City.

There are many varieties and names for storms:

• Blizzard – There are varying definitions for blizzards, both over time and by location. In general, a blizzard is accompanied by gale-force winds, heavy snow (accumulating at a rate of at least 5 centimeters (2 in) per hour), and very cold conditions (below approximately −10 degrees Celsius or 14 F). Lately, the temperature criterion has fallen out of the definition across the United States
• Bomb cyclone – A rapid deepening of a mid-latitude cyclonic low-pressure area, typically occurring over the ocean, but can occur over land. The winds experienced during these storms can be as powerful as that of a typhoon or hurricane.
• Coastal Storm – Large wind waves and/or storm surge that strike the coastal zone. Their impacts include coastal erosion and coastal flooding
• Derecho – A derecho is a widespread, long-lived, straight-line wind storm that is associated with a land-based, fast-moving group of severe thunderstorms.
• Dust devil – A small, localized updraft of rising air.
• Dust storm – A situation in which winds pick up large quantities of sand or soil, greatly reducing the visibility
• Firestorm – Firestorms are conflagrations which attain such intensity that they create and sustain their own wind systems. It is most commonly a natural phenomenon, created during some of the largest bushfires, forest fires, and wildfires. The Peshtigo Fire is one example of a firestorm. Firestorms can also be deliberate effects of targeted explosives such as occurred as a result of the aerial bombings of Dresden. Nuclear detonations generate firestorms if high winds are not present.
• Gale – An extratropical storm with sustained winds between 34–48 knots (39–55 mph or 63–90 km/h).
• Hailstorm – A type of storm that precipitates round chunks of ice. Hailstorms usually occur during regular thunderstorms. While most of the hail that precipitates from the clouds is fairly small and virtually harmless, there are occasional occurrences of hail greater than 2 inches (5 cm) in diameter that can cause much damage and injuries.
• Hypercane – A hypothetical tropical cyclone that could potentially form over 50 °C (122 °F) water. Such a storm would produce winds of over 800 km/h (500 mph). A series of hypercanes may have formed during the asteroid or comet impact that killed the non-avian dinosaurs 66 million years ago. Such a phenomenon could also occur during a supervolcanic eruption, or extreme global warming.
• Ice storm –  Ice storms are one of the most dangerous forms of winter storms. When surface temperatures are below freezing, but a thick layer of above-freezing air remains aloft, rain can fall into the freezing layer and freeze upon impact into a glaze of ice. In general, 8 millimetres (0.31 in) of accumulation is all that is required, especially in combination with breezy conditions, to start downing power lines as well as tree limbs. Ice storms also make unheated road surfaces too slick to drive upon. Ice storms can vary in time range from hours to days and can cripple small towns and large metropolitan cities alike.
• Microburst – A very powerful windstorm produced during a thunderstorm that only lasts a few minutes.
• Ocean Storm or sea storm – Storm conditions out at sea are defined as having sustained winds of 48 knots (55 mph or 90 km/h) or greater. Usually just referred to as a storm, these systems can sink vessels of all types and sizes.
• Snowstorm – A heavy fall of snow accumulating at a rate of more than 5 centimeters (2 in) per hour that lasts several hours. Snow storms, especially ones with a high liquid equivalent and breezy conditions, can down tree limbs, cut off power connections and paralyze travel over large regions.
• Squall – Sudden onset of wind increase of at least 16 knots (30 km/h) or greater sustained for at least one minute.
• Thunderstorm – A thunderstorm is a type of storm that generates both lightning and thunder. It is normally accompanied by heavy precipitation. Thunderstorms occur throughout the world, with the highest frequency in tropical rainforest regions where there are conditions of high humidity and temperature along with atmospheric instability. These storms occur when high levels of condensation form in a volume of unstable air that generates deep, rapid, upward motion in the atmosphere. The heat energy creates powerful rising air currents that swirl upwards to the tropopause. Cool descending air currents produce strong downdraughts below the storm. After the storm has spent its energy, the rising currents die away and downdraughts break up the cloud. Individual storm clouds can measure 2–10 km across.
• Tornado – A tornado is a violent, destructive whirlwind storm occurring on land. Usually its appearance is that of a dark, funnel-shaped cloud. Often tornadoes are preceded by or associated with thunderstorms and a wall cloud. They are often called the most destructive of storms, and while they form all over the planet, the interior of the United States is the most prone area, especially throughout Tornado Alley.
• Tropical cyclone – A tropical cyclone is a storm system with a closed circulation around a centre of low pressure, fueled by the heat released when moist air rises and condenses. The name underscores its origin in the tropics and their cyclonic nature. Tropical cyclones are distinguished from other cyclonic storms such as nor'easters and polar lows by the heat mechanism that fuels them, which makes them "warm core" storm systems. Tropical cyclones form in the oceans if the conditions in the area are favorable, and depending on their strength and location, there are various terms by which they are called, such as tropical depression, tropical storm, hurricane and typhoon.
• Wind storm – A storm marked by high wind with little or no precipitation. Windstorm damage often opens the door for massive amounts of water and debris to cause further damage to a structure. European windstorms and derechos are two type of windstorms. High wind is also the cause of sandstorms in dry climates.

Classification

A strict meteorological definition of a terrestrial storm is a wind measuring 10 or higher on the Beaufort scale, meaning a wind speed of 24.5 m/s (89 km/h, 55 mph) or more; however, popular usage is not so restrictive. Storms can last anywhere from 12 to 200 hours, depending on season and geography. In North America, the east and northeast storms are noted for the most frequent repeatability and duration, especially during the cold period. Big terrestrial storms alter the oceanographic conditions that in turn may affect food abundance and distribution: strong currents, strong tides, increased siltation, change in water temperatures, overturn in the water column, etc.

Extraterrestrial storms

The Great Red Spot on Jupiter

Storms do not only occur on Earth; other planetary bodies with a sufficient atmosphere (gas giants in particular) also undergo stormy weather. The Great Red Spot on Jupiter provides a well-known example. Though technically an anticyclone, with greater than hurricane wind speeds, it is larger than the Earth and has persisted for at least 340 years, having first been observed by astronomer Galileo Galilei. Neptune also had its own lesser-known Great Dark Spot.

In September 1994, the Hubble telescope – using Wide Field Planetary Camera 2 – imaged storms on Saturn generated by upwelling of warmer air, similar to a terrestrial thunderhead. The east-west extent of the same-year storm equalled the diameter of Earth. The storm was observed earlier in September 1990 and acquired the name Dragon Storm.

The dust storms of Mars vary in size, but can often cover the entire planet. They tend to occur when Mars comes closest to the Sun, and have been shown to increase the global temperature.

One particularly large Martian storm was exhaustively studied up close due to coincidental timing. When the first spacecraft to successfully orbit another planet, Mariner 9, arrived and successfully orbited Mars on 14 November 1971, planetary scientists were surprised to find the atmosphere was thick with a planet-wide robe of dust, the largest storm ever observed on Mars. The surface of the planet was totally obscured. Mariner 9's computer was reprogrammed from Earth to delay imaging of the surface for a couple of months until the dust settled, however, the surface-obscured images contributed much to the collection of Mars atmospheric and planetary surface science.

Two extrasolar planets are known to have storms: HD 209458 b and HD 80606 b. The former's storm was discovered on June 23, 2010 and measured at 6,200 km/h, while the latter produces winds of 17,700 kilometers (11,000 mi) per hour across the surface. The spin of the planet then creates giant swirling shock-wave storms that carry the heat aloft.

Effects on human society

"Storm damage" redirects here. For the British television film, see Storm Damage.

A snow blockade in southern Minnesota in 1881

 

A return stroke, cloud-to-ground lightning strike during a thunderstorm.

 

A sunshower storm in the Mojave desert at sunset.

Shipwrecks are common with the passage of strong tropical cyclones. Such shipwrecks can change the course of history, as well as influence art and literature. A hurricane led to a victory of the Spanish over the French for control of Fort Caroline, and ultimately the Atlantic coast of North America, in 1565.

Strong winds from any storm type can damage or destroy vehicles, buildings, bridges, and other outside objects, turning loose debris into deadly flying projectiles. In the United States, major hurricanes comprise just 21% of all landfalling tropical cyclones, but account for 83% of all damage. Tropical cyclones often knock out power to tens or hundreds of thousands of people, preventing vital communication and hampering rescue efforts. Tropical cyclones often destroy key bridges, overpasses, and roads, complicating efforts to transport food, clean water, and medicine to the areas that need it. Furthermore, the damage caused by tropical cyclones to buildings and dwellings can result in economic damage to a region, and to a diaspora of the population of the region.

The storm surge, or the increase in sea level due to the cyclone, is typically the worst effect from landfalling tropical cyclones, historically resulting in 90% of tropical cyclone deaths. The relatively quick surge in sea level can move miles/kilometers inland, flooding homes and cutting off escape routes. The storm surges and winds of hurricanes may be destructive to human-made structures, but they also stir up the waters of coastal estuaries, which are typically important fish breeding locales.

Cloud-to-ground lightning frequently occurs within the phenomena of thunderstorms and have numerous hazards towards landscapes and populations. One of the more significant hazards lightning can pose is the wildfires they are capable of igniting. Under a regime of low precipitation (LP) thunderstorms, where little precipitation is present, rainfall cannot prevent fires from starting when vegetation is dry as lightning produces a concentrated amount of extreme heat. Wildfires can devastate vegetation and the biodiversity of an ecosystem. Wildfires that occur close to urban environments can inflict damages upon infrastructures, buildings, crops, and provide risks to explosions, should the flames be exposed to gas pipes. Direct damage caused by lightning strikes occurs on occasion. In areas with a high frequency for cloud-to-ground lightning, like Florida, lightning causes several fatalities per year, most commonly to people working outside.

Precipitation with low potential of hydrogen levels (pH), otherwise known as acid rain, is also a frequent risk produced by lightning. Distilled water, which contains no carbon dioxide, has a neutral pH of 7. Liquids with a pH less than 7 are acidic, and those with a pH greater than 7 are bases. "Clean" or unpolluted rain has a slightly acidic pH of about 5.2, because carbon dioxide and water in the air react together to form carbonic acid, a weak acid (pH 5.6 in distilled water), but unpolluted rain also contains other chemicals. Nitric oxide present during thunderstorm phenomena, caused by the splitting of nitrogen molecules, can result in the production of acid rain, if nitric oxide forms compounds with the water molecules in precipitation, thus creating acid rain. Acid rain can damage infrastructures containing calcite or other solid chemical compounds containing carbon. In ecosystems, acid rain can dissolve plant tissues of vegetations and increase acidification process in bodies of water and in soil, resulting in deaths of marine and terrestrial organisms.

Hail damage to roofs often goes unnoticed until further structural damage is seen, such as leaks or cracks. It is hardest to recognize hail damage on shingled roofs and flat roofs, but all roofs have their own hail damage detection problems. Metal roofs are fairly resistant to hail damage, but may accumulate cosmetic damage in the form of dents and damaged coatings. Hail is also a common nuisance to drivers of automobiles, severely denting the vehicle and cracking or even shattering windshields and windows. Rarely, massive hailstones have been known to cause concussions or fatal head trauma. Hailstorms have been the cause of costly and deadly events throughout history. One of the earliest recorded incidents occurred around the 9th century in Roopkund, Uttarakhand, India. The largest hailstone in terms of diameter and weight ever recorded in the United States fell on July 23, 2010 in Vivian, South Dakota in the United States; it measured 8 inches (20 cm) in diameter and 18.62 inches (47.3 cm) in circumference, weighing in at 1.93 pounds (0.88 kg). This broke the previous record for diameter set by a hailstone 7 inches diameter and 18.75 inches circumference which fell in Aurora, Nebraska in the United States on June 22, 2003, as well as the record for weight, set by a hailstone of 1.67 pounds (0.76 kg) that fell in Coffeyville, Kansas in 1970.

Various hazards, ranging from hail to lightning can affect outside technology facilities, such as antennas, satellite dishes, and towers. As a result, companies with outside facilities have begun installing such facilities underground, in order to reduce the risk of damage from storms.

Substantial snowfall can disrupt public infrastructure and services, slowing human activity even in regions that are accustomed to such weather. Air and ground transport may be greatly inhibited or shut down entirely. Populations living in snow-prone areas have developed various ways to travel across the snow, such as skis, snowshoes, and sleds pulled by horses, dogs, or other animals and later, snowmobiles. Basic utilities such as electricity, telephone lines, and gas supply can also fail. In addition, snow can make roads much harder to travel and vehicles attempting to use them can easily become stuck.

The combined effects can lead to a "snow day" on which gatherings such as school, work, or church are officially canceled. In areas that normally have very little or no snow, a snow day may occur when there is only light accumulation or even the threat of snowfall, since those areas are unprepared to handle any amount of snow. In some areas, such as some states in the United States, schools are given a yearly quota of snow days (or "calamity days"). Once the quota is exceeded, the snow days must be made up. In other states, all snow days must be made up. For example, schools may extend the remaining school days later into the afternoon, shorten spring break, or delay the start of summer vacation.

Accumulated snow is removed to make travel easier and safer, and to decrease the long-term effect of a heavy snowfall. This process utilizes shovels and snowplows, and is often assisted by sprinkling salt or other chloride-based chemicals, which reduce the melting temperature of snow. In some areas with abundant snowfall, such as Yamagata Prefecture, Japan, people harvest snow and store it surrounded by insulation in ice houses. This allows the snow to be used through the summer for refrigeration and air conditioning, which requires far less electricity than traditional cooling methods.

Agriculture

Hail can cause serious damage, notably to automobiles, aircraft, skylights, glass-roofed structures, livestock, and most commonly, farmers' crops. Wheat, corn, soybeans, and tobacco are the most sensitive crops to hail damage. Hail is one of Canada's most expensive hazards. Snowfall can be beneficial to agriculture by serving as a thermal insulator, conserving the heat of the Earth and protecting crops from subfreezing weather. Some agricultural areas depend on an accumulation of snow during winter that will melt gradually in spring, providing water for crop growth. If it melts into water and refreezes upon sensitive crops, such as oranges, the resulting ice will protect the fruit from exposure to lower temperatures. Although tropical cyclones take an enormous toll in lives and personal property, they may be important factors in the precipitation regimes of places they affect and bring much-needed precipitation to otherwise dry regions. Hurricanes in the eastern north Pacific often supply moisture to the Southwestern United States and parts of Mexico. Japan receives over half of its rainfall from typhoons. Hurricane Camille averted drought conditions and ended water deficits along much of its path, though it also killed 259 people and caused $9.14 billion (2005 USD) in damage.

Aviation

Effect of wind shear on aircraft trajectory. Merely correcting for the initial gust front can have dire consequences.

Hail is one of the most significant thunderstorm hazards to aircraft. When hail stones exceed 0.5 inches (13 mm) in diameter, planes can be seriously damaged within seconds. The hailstones accumulating on the ground can also be hazardous to landing aircraft. Strong wind outflow from thunderstorms causes rapid changes in the three-dimensional wind velocity just above ground level. Initially, this outflow causes a headwind that increases airspeed, which normally causes a pilot to reduce engine power if they are unaware of the wind shear. As the aircraft passes into the region of the downdraft, the localized headwind diminishes, reducing the aircraft's airspeed and increasing its sink rate. Then, when the aircraft passes through the other side of the downdraft, the headwind becomes a tailwind, reducing lift generated by the wings, and leaving the aircraft in a low-power, low-speed descent. This can lead to an accident if the aircraft is too low to effect a recovery before ground contact. As the result of the accidents in the 1970s and 1980s, in 1988 the U.S. Federal Aviation Administration mandated that all commercial aircraft have on-board wind shear detection systems by 1993. Between 1964 and 1985, wind shear directly caused or contributed to 26 major civil transport aircraft accidents in the U.S. that led to 620 deaths and 200 injuries. Since 1995, the number of major civil aircraft accidents caused by wind shear has dropped to approximately one every ten years, due to the mandated on-board detection as well as the addition of Doppler weather radar units on the ground. (NEXRAD)

Recreation

Many winter sports, such as skiing, snowboarding, snowmobiling, and snowshoeing depend upon snow. Where snow is scarce but the temperature is low enough, snow cannons may be used to produce an adequate amount for such sports. Children and adults can play on a sled or ride in a sleigh. Although a person's footsteps remain a visible lifeline within a snow-covered landscape, snow cover is considered a general danger to hiking since the snow obscures landmarks and makes the landscape itself appear uniform.

Notable storms in art and culture

The Great Wave off Kanagawa, an ukiyo-e print by Hokusai

In mythology and literature

According to the Bible, a giant storm sent by God flooded the Earth. Noah and his family and the animals entered the Ark, and "the same day were all the fountains of the great deep broken up, and the windows of heaven were opened, and the rain was upon the earth forty days and forty nights." The flood covered even the highest mountains to a depth of more than twenty feet, and all creatures died; only Noah and those with him on the Ark were left alive. In the New Testament, Jesus Christ is recorded to have calmed a storm on the Sea of Galilee.

See also: Genesis flood myth

The Gilgamesh flood myth is a deluge story in the Epic of Gilgamesh.

In Greek mythology Aeolus, keeper of storm-winds, squalls and tempests.

The Sea Venture was wrecked near Bermuda in 1609, which led to the colonization of Bermuda and provided the inspiration for Shakespeare's play The Tempest(1611). Specifically, Sir Thomas Gates, future governor of Virginia, was on his way to England from Jamestown, Virginia. On Saint James Day, while he was between Cuba and the Bahamas, a hurricane raged for nearly two days. Though one of the small vessels in the fleet sank to the bottom of the Florida Straits, seven of the remaining vessels reached Virginia within several days after the storm. The flagship of the fleet, known as Sea Adventure, disappeared and was presumed lost. A small bit of fortune befell the ship and her crew when they made landfall on Bermuda. The vessel was damaged on a surrounding coral reef, but all aboard survived for nearly a year on the island. The British colonists claimed the island and quickly settled Bermuda. In May 1610, they set forth for Jamestown, this time arriving at their destination.

The children's novel The Wonderful Wizard of Oz, written by L. Frank Baum and illustrated by W. W. Denslow, chronicles the adventures of a young girl named Dorothy Gale in the Land of Oz, after being swept away from her Kansas farm home by a tornado. The story was originally published by the George M. Hill Company in Chicago on May 17, 1900 and has since been reprinted numerous times, most often under the name The Wizard of Oz, and adapted for use in other media. Thanks in part to the 1939 MGM movie, it is one of the best-known stories in American popular culture and has been widely translated. Its initial success, and the success of the popular 1902 Broadway musical which Baum adapted from his original story, led to Baum's writing thirteen more Oz books.

Hollywood director King Vidor (February 8, 1894 – November 1, 1982) survived the Galveston Hurricane of 1900 as a boy. Based on that experience, he published a fictionalized account of that cyclone, titled "Southern Storm", for the May 1935 issue of Esquire magazine. Erik Larson excerpts a passage from that article in his 2005 book, Isaac's Storm:

I remember now that it seemed as if we were in a bowl looking up toward the level of the sea. As we stood there in the sandy street, my mother and I, I wanted to take my mother's hand and hurry her away. I felt as if the sea was going to break over the edge of the bowl and come puring down upon us.

Numerous other accounts of the Galveston Hurricane of 1900 have been made in print and in film. Larson cites many of them in Isaac's Storm, which centrally features that storm, as well as chronicles the creation of the Weather Bureau (which came to known as the National Weather Service) and that agency's fateful rivalry with the weather service in Cuba, and a number of other major storms, such as those which ravaged Indianola, Texas in 1875 and 1886.

The Great Storm of 1987 is key in an important scene near the end of Possession: A Romance, the bestselling and Man Booker Prize-winning novel by A. S. Byatt. The Great Storm of 1987 occurred on the night of October 15–16, 1987, when an unusually strong weather system caused winds to hit much of southern England and northern France. It was the worst storm to hit England since the Great Storm of 1703 (284 years earlier) and was responsible for the deaths of at least 22 people in England and France combined (18 in England, at least four in France).

Hurricane Katrina (2005) has been featured in a number of works of fiction.

In fine art

Rembrandt's The Storm on the Sea of Galilee.

The Romantic seascape painters J. M. W. Turner and Ivan Aivazovsky created some of the most lasting impressions of the sublime and stormy seas that are firmly imprinted on the popular mind. Turner's representations of powerful natural forces reinvented the traditional seascape during the first half of the nineteenth century.

Upon his travels to Holland, he took note of the familiar large rolling waves of the English seashore transforming into the sharper, choppy waves of a Dutch storm. A characteristic example of Turner's dramatic seascape is The Slave Ship of 1840. Aivazovsky left several thousand turbulent canvases in which he increasingly eliminated human figures and historical background to focus on such essential elements as light, sea, and sky. His grandiose Ninth Wave (1850) is an ode to human daring in the face of the elements.

In motion pictures

The 1926 silent film The Johnstown Flood features the Great Flood of 1889 in Johnstown, Pennsylvania. The flood, caused by the catastrophic failure of the South Fork Dam after days of extremely heavy rainfall, prompted the first major disaster relief effort by the American Red Cross, directed by Clara Barton. The Johnstown Flood was depicted in numerous other media (both fictional and in non-fiction), as well.

Warner Bros.' 2000 dramatic disaster film The Perfect Storm, directed by Wolfgang Petersen, is an adaptation of Sebastian Junger's 1997 non-fiction book of the same title. The book and film feature the crew of the Andrea Gail, which got caught in the Perfect Storm of 1991. The 1991 Perfect Storm, also known as the Halloween Nor'easter of 1991, was a nor'easter that absorbed Hurricane Grace and ultimately evolved into a small hurricane late in its life cycle.

In music

Storms have also been portrayed in many works of music. Examples of storm music include Vivaldi's Four Seasons violin concerto RV 315 (Summer) (third movement: Presto), Beethoven's Pastoral Symphony (the fourth movement), a scene in Act II of Rossini's opera The Barber of Seville, the third act of Giuseppe Verdi's Rigoletto, and the fifth (Cloudburst) movement of Ferde Grofé's Grand Canyon Suite.

Extreme weather or extreme climate events includes unexpected, unusual, severe, or unseasonal weather; weather at the extremes of the historical distribution—the range that has been seen in the past. Often, extreme events are based on a location's recorded weather history and defined as lying in the most unusual ten percent.

There is evidence to suggest that climate change is increasing the periodicity and intensity of some extreme weather events. Confidence in the attribution of extreme weather and other events to anthropogenic climate change is highest in changes in frequency or magnitude of extreme heat and cold events with some confidence in increases in heavy precipitation and increases in intensity of droughts.

Extreme weather has significant impacts on human society as well as natural ecosystems. For example, a global insurer Munich Re estimates that natural disasters cause more than $90 billion global direct losses in 2015.

Extreme weather events

Heat waves

2003 European heat wave

Heat waves are periods of abnormally high temperatures and heat index. Definitions of a heatwave vary because of the variation of temperatures in different geographic locations. Excessive heat is often accompanied by high levels of humidity, but can also be catastrophically dry.

Because heat waves are not visible as other forms of severe weather are, like hurricanes, tornadoes, and thunderstorms, they are one of the less known forms of extreme weather. Severe heat weather can damage populations and crops due to potential dehydration or hyperthermia, heat cramps, heat expansion and heat stroke. Dried soils are more susceptible to erosion, decreasing lands available for agriculture. Outbreaks of wildfires can increase in frequency as dry vegetation has increased likeliness of igniting. The evaporation of bodies of water can be devastating to marine populations, decreasing the size of the habitats available as well as the amount of nutrition present within the waters. Livestock and other animal populations may decline as well.

During excessive heat, plants shut their leaf pores (stomata), a protective mechanism to conserve water but also curtails plants' absorption capabilities. This leaves more pollution and ozone in the air, which leads to higher mortality in the population. It has been estimated that extra pollution during the hot summer 2006 in the UK, cost 460 lives. The European heat waves from summer 2003 are estimated to have caused 30,000 excess deaths, due to heat stress and air pollution. Over 200 U.S cities have registered new record high temperatures. The worst heat wave in the USA occurred in 1936 and killed more than 5000 people directly. The worst heat wave in Australia occurred in 1938–39 and killed 438. The second worst was in 1896.

Power outages can also occur within areas experiencing heat waves due to the increased demand for electricity (i.e. air conditioning use). The urban heat island effect can increase temperatures, particularly overnight.

Cold waves

Cold wave in continental North America from Dec-03 to Dec-10, 2013. Red color means above mean temperature; blue represents below normal temperature.

A cold wave is a weather phenomenon that is distinguished by a cooling of the air. Specifically, as used by the U.S. National Weather Service, a cold wave is a rapid fall in temperature within a 24-hour period requiring substantially increased protection to agriculture, industry, commerce, and social activities. The precise criterion for a cold wave is determined by the rate at which the temperature falls, and the minimum to which it falls. This minimum temperature is dependent on the geographical region and time of year. Cold waves generally are capable of occurring any geological location and are formed by large cool air masses that accumulate over certain regions, caused by movements of air streams.

A cold wave can cause death and injury to livestock and wildlife. Exposure to cold mandates greater caloric intake for all animals, including humans, and if a cold wave is accompanied by heavy and persistent snow, grazing animals may be unable to reach necessary food and water, and die of hypothermia or starvation. Cold waves often necessitate the purchase of fodder for livestock at considerable cost to farmers. Human populations can be inflicted with frostbite when exposed for extended periods of time to cold and may result in the loss of limbs or damage to internal organs.

Extreme winter cold often causes poorly insulated water pipes to freeze. Even some poorly protected indoor plumbing may rupture as frozen water expands within them, causing property damage. Fires, paradoxically, become more hazardous during extreme cold. Water mains may break and water supplies may become unreliable, making firefighting more difficult.

Cold waves that bring unexpected freezes and frosts during the growing season in mid-latitude zones can kill plants during the early and most vulnerable stages of growth. This results in crop failure as plants are killed before they can be harvested economically. Such cold waves have caused famines. Cold waves can also cause soil particles to harden and freeze, making it harder for plants and vegetation to grow within these areas. One extreme was the so-called Year Without a Summer of 1816, one of several years during the 1810s in which numerous crops failed during freakish summer cold snaps after volcanic eruptions reduced incoming sunlight.

Tropical cyclones

Play media

NASA film In Katrina's Wake, covering the impacts from Hurricane Katrina.

On June 12, 2020, the National Oceanic and Atmospheric Administration (NOAA) of the U.S. government predicted that, over the 21st Century, the frequency of tropical storms and Atlantic hurricanes would decline by 25 percent while their maximum intensity would rise 5 percent. Prior to the new study there was a decade-long debate about a possible increase of tropical cyclones as an effect of climate change. However, the 2012 IPCC special report on extreme events SREX states that "there is low confidence in any observed long-term (i.e., 40 years or more) increases in tropical cyclone activity (i.e., intensity, frequency, duration), after accounting for past changes in observing capabilities." Increases in population densities increase the number of people affected and damage caused by an event of given severity. The World Meteorological Organization and the U.S. Environmental Protection Agency have in the past linked increasing extreme weather events to climate change, as have Hoyos et al. (2006), writing that the increasing number of category 4 and 5 hurricanes is directly linked to increasing temperatures. Similarly, Kerry Emanuel in Nature writes that hurricane power dissipation is highly correlated with temperature, reflecting climate change.

Hurricane modeling has produced similar results, finding that hurricanes, simulated under warmer, high CO₂ conditions, are more intense than under present-day conditions. Thomas Knutson and Robert E. Tuleya of the NOAA stated in 2004 that warming-induced by greenhouse gas may lead to the increasing occurrence of highly destructive category-5 storms. Vecchi and Soden find that wind shear, the increase of which acts to inhibit tropical cyclones, also changes in model-projections of climate change. There are projected increases of wind shear in the tropical Atlantic and East Pacific associated with the deceleration of the Walker circulation, as well as decreases of wind shear in the western and central Pacific. The study does not make claims about the net effect on Atlantic and East Pacific hurricanes of the warming and moistening atmospheres, and the model-projected increases in Atlantic wind shear.

Research and attribution

Early research in extreme weather focused on statements about predicting certain events, contemporary research has focused more on attribution of causes to trends in events. In particular the field is focusing on climate change alongside other causal factors for these events.

Definitions of extreme weather vary in different parts of the scientific community, changing the outcomes of research from those fields. Generally speaking, one event in extreme weather cannot be attributed to any one cause; however, certain system wide changes to global weather systems can lead to increased frequency or intensity of extreme weather events.

A 2016 report from the National Academies of Sciences, Engineering, and Medicine, recommended investing in improved shared practices across the field working on attribution research, improving the connection between research outcomes and weather forecasting.

As more research is done in this area, scientists have begun to investigate the connection between climate change and extreme weather events and what future impacts may arise. Much of this work is done through climate modeling. Climate models provide important predictions about the future characteristics of the atmosphere, oceans, and Earth using data collected in the modern day. However, while climate models are vital for studying more complex processes such as climate change or ocean acidification, they are still only approximations. Moreover, weather events are complex and cannot be tied to a singular cause -- there are often many atmospheric variables such as temperature, pressure, or moisture to note on top of any influences from climate change or natural variability.

An important record of extreme weather events is gathered statistics from around the world, which can help scientists and policymakers to have a better understanding of any changes in weather and climate conditions. These statistics can influence climate modeling as well. Statistics have shown an increase in extreme weather events throughout the 1900s and into the 2000s.

In a report published by the United Nations Office for Disaster Risk Reduction (UNDRR), it was shown that there were around 6,681 climate-related events reported during 2000-2019, compared to 3,656 climate-related events reported during 1980-1999. In this report, a ‘climate-related event’ refers to floods, storms, droughts, landslides, extreme temperatures (like heat waves or freezes), and wildfires; it excludes geophysical events such as volcanic eruptions, earthquakes, or mass movements. While there is evidence that a changing global climate, such as an increase in temperature, has impacted the frequency of extreme weather events, the most significant effects are likely to arise in the future. This is where climate models are useful, for they can provide simulations on how the atmosphere may behave over time and what steps need to be taken in the present day to mitigate any negative changes.

Of course, there are errors associated with statistic-based data. Over or under reporting of casualties or losses can lead to inaccuracy in the impact of extreme weather. As science and technology has improved throughout the twentieth and twenty-first centuries, some researchers attribute increases in extreme weather occurrences to more reliable reporting systems. A difference in what qualifies as ‘extreme weather’ in varying climate systems could also be argued. However, the UNDRR report shows that, although some countries have experienced greater effects, there have been increases in extreme weather events on all continents. Current evidence and climate models show that an increasing global temperature will intensify extreme weather events around the globe, thereby amplifying human loss, damages and economic costs, and ecosystem destruction.

Attribution to natural variability

Aspects of our climate system have a certain level of natural variability, and extreme weather events can occur for several reasons beyond human impact, including changes in pressure or the movement of air. Areas along the coast or located in tropical regions are more likely to experience storms with heavy precipitation than temperate regions, although such events can occur. Not every unusual weather event can be blamed on climate change. The atmosphere is a complex and dynamic system, influenced by several factors such as the natural tilt and orbit of the Earth, the absorption or reflection of solar radiation, the movement of air masses, and the hydrologic cycle. Due to this, weather patterns can experience some variation, and so extreme weather can be attributed, at least in part, to the natural variability that exists on Earth. Climatic variations such as the El Niño-Southern Oscillation or the North Atlantic Oscillation impact weather patterns in specific regions of the world, influencing temperature and precipitation. The record-breaking extreme weather events that have been catalogued throughout the past two hundred years most likely arise when climate patterns like ENSO or NAO work “in the same direction as human‐induced warming."

Attribution to climate change

In general, climate models show that with climate change, the planet will experience more extreme weather. Storms such as hurricanes or tropical cyclones may experience greater rainfall, causing major flooding events or landslides by saturating soil. This is because warmer air is able to ‘hold’ more moisture due to the water molecules having increased kinetic energy, and precipitation occurs at a greater rate because more molecules have the critical speed needed to fall as rain drops. A shift in rainfall patterns can lead to greater amounts of precipitation in one area while another experiences much hotter, drier conditions, which can lead to drought. This is because an increase in temperatures also lead to an increase in evaporation at the surface of the earth, so more precipitation does not necessarily mean universally wetter conditions or a worldwide increase in drinking water.

Some studies assert a connection between rapidly warming arctic temperatures and thus a vanishing cryosphere to extreme weather in mid-latitudes. In a study published in Nature in 2019, scientists used several simulations to determine that the melting of ice sheets in Greenland and Antarctica could affect overall sea level and sea temperature. Other models have shown that modern temperature rise and the subsequent addition of meltwater to the ocean could lead to a disruption of the thermohaline circulation, which is responsible for the movement of seawater and distribution of heat around the globe. A collapse of this circulation in the northern hemisphere could lead to an increase in extreme temperatures in Europe, as well as more frequent storms by throwing off natural climate variability and conditions. Thus, as increasing temperatures cause glaciers to melt, mid-latitudes could experience shifts in weather patterns or temperatures.

Impact of human activity

Another important area of research, on top of the factors that may cause or increase the occurrence of extreme weather events, is to examine what might amplify the effects of extreme weather. One of the major influences is human activity. While burning fossil fuels is the most obvious way that humans have influenced extreme weather events, there are plenty of other anthropogenic activities that can exacerbate the effects of such events.

Urban planning often amplifies flooding impacts, especially in areas that are at increased risk of storms due to their location and climate variability. First, increasing the amount of impervious surfaces, such as sidewalks, roads, and roofs, means that less of the water from incoming storms is absorbed by the land. The destruction of wetlands, which act as a natural reservoir by absorbing water, can intensify the impact of floods and extreme precipitation. This can happen both inland and at the coast. However, wetland destruction along the coast can mean decreasing an area’s natural ‘cushion,’ thus allowing storm surges and flood waters to reach farther inland during hurricanes or cyclones. Building homes below sea level or along a floodplain puts residents at increased risk of destruction or injury in an extreme precipitation event.

More urban areas can also contribute to the rise of extreme or unusual weather events. Tall structures can alter the way that wind moves throughout an urban area, pushing warmer air upwards and inducing convection, creating thunderstorms. With these thunderstorms comes increased precipitation, which, because of the large amounts of impervious surfaces in cities, can have devastating impacts. Impervious surfaces also absorb energy from the sun and warm the atmosphere, causing drastic increases in temperatures in urban areas. This, along with pollution and heat released from cars and other anthropogenic sources, contributes to urban heat islands.  As temperatures continue to rise due to anthropogenic emissions, heat waves could become more common or threatening in urban areas. Additionally, high population density in cities exacerbates human loss in many extreme weather events. Overall, while human activity can have a direct impact on weather patterns, it's just as important to consider how human actions might exacerbate the effects and losses from extreme weather events.

Effects

A tornado that struck Anadarko, Oklahoma during a tornado outbreak in 1999

The effects of extreme weather includes, but not limited to:

• Too much rain (heavy downpours), causes floods and landslides
• Too much heat and no rain (heatwave) drought and wildfires
• Strong winds, such as hurricanes and tornadoes = damage to man made structures and animal habitats
• Large snowfalls = avalanches and blizzards

Changes in human society

Economic cost

According to IPCC (2011) estimates of annual losses have ranged since 1980 from a few billion to above US$200 billion (in 2010 dollars), with the highest value for 2005 (the year of Hurricane Katrina). The global weather-related disaster losses, such as loss of human lives, cultural heritage, and ecosystem services, are difficult to value and monetize, and thus they are poorly reflected in estimates of losses. Yet, recent abnormally intense storms, hurricanes, floods, heatwaves, droughts and associated large-scale wildfires have led to unprecedented negative ecological consequences for tropical forests and coral reefs around the world.

Loss of life

The death toll from natural disasters has declined over 90 percent since the 1920s, according to the International Disaster Database, even as the total human population on Earth quadrupled, and temperatures rose 1.3°C. In the 1920s, 5.4 million people died from natural disasters while in the 2010s, just 400,000 did.

The most dramatic and rapid declines in deaths from extreme weather events have taken place in south Asia. Where a tropical cyclone in 1991 in Bangladesh killed 135,000 people, and a 1970 cyclone killed 300,000, the similarly-sized Cyclone Ampham, which struck India and Bangladesh in 2020, killed just 120 people in total.

On July 23, 2020, Munich Re announced that the 2,900 total global deaths from natural disasters for the first half of 2020 was a record-low, and “much lower than the average figures for both the last 30 years and the last 10 years.”

Changes in ecosystems

Extreme weather negatively affects the ecosystems through various events resulting the serious impact on the landscape and people.

In many cases wildfires provide growth and rid of the abundant weeds and other dry plants that build up over time, that cause the beginnings of rampant wildfires. Although there are beneficial events from wildfires it also effects ecosystems of animals, plants, and even human societies. These events cause the ground to be more dry and in turn create more wildfires while also causing erosion that leads to dangerous landfall. Wildfires also cause a disruption in carbon cycles which can affect water quality and land settings in the area.

Extreme value theory

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Extreme_value_theory 

Extreme value theory is used to model the risk of extreme, rare events, such as the 1755 Lisbon earthquake.

Extreme value theory or extreme value analysis (EVA) is a branch of statistics dealing with the extreme deviations from the median of probability distributions. It seeks to assess, from a given ordered sample of a given random variable, the probability of events that are more extreme than any previously observed. Extreme value analysis is widely used in many disciplines, such as structural engineering, finance, earth sciences, traffic prediction, and geological engineering. For example, EVA might be used in the field of hydrology to estimate the probability of an unusually large flooding event, such as the 100-year flood. Similarly, for the design of a breakwater, a coastal engineer would seek to estimate the 50-year wave and design the structure accordingly.

Data analysis

Two main approaches exist for practical extreme value analysis.

The first method relies on deriving block maxima (minima) series as a preliminary step. In many situations it is customary and convenient to extract the annual maxima (minima), generating an "Annual Maxima Series" (AMS).

The second method relies on extracting, from a continuous record, the peak values reached for any period during which values exceed a certain threshold (falls below a certain threshold). This method is generally referred to as the "Peak Over Threshold" method (POT).

For AMS data, the analysis may partly rely on the results of the Fisher–Tippett–Gnedenko theorem, leading to the generalized extreme value distribution being selected for fitting. However, in practice, various procedures are applied to select between a wider range of distributions. The theorem here relates to the limiting distributions for the minimum or the maximum of a very large collection of independent random variables from the same distribution. Given that the number of relevant random events within a year may be rather limited, it is unsurprising that analyses of observed AMS data often lead to distributions other than the generalized extreme value distribution (GEVD) being selected.

For POT data, the analysis may involve fitting two distributions: one for the number of events in a time period considered and a second for the size of the exceedances.

A common assumption for the first is the Poisson distribution, with the generalized Pareto distribution being used for the exceedances. A tail-fitting can be based on the Pickands–Balkema–de Haan theorem.

Novak reserves the term “POT method” to the case where the threshold is non-random, and distinguishes it from the case where one deals with exceedances of a random threshold.

Applications

Applications of extreme value theory include predicting the probability distribution of:

• Extreme floods; The size of freak waves
• Tornado outbreaks
• Maximum sizes of ecological populations
• Side effects of drugs (e.g., Ximelagatran)
• The amounts of large insurance losses
• Equity risks; Day to day market risk
• Mutational events during evolution
• Large wildfires
• Environmental loads on structures
• Estimate fastest time humans are capable of running the 100 metres sprint and performances in other athletic disciplines
• Pipeline failures due to pitting corrosion
• Anomalous IT network traffic, prevent attackers from reaching important data
• Road safety analysis
• Wireless communications
• Epidemics

History

The field of extreme value theory was pioneered by Leonard Tippett (1902–1985). Tippett was employed by the British Cotton Industry Research Association, where he worked to make cotton thread stronger. In his studies, he realized that the strength of a thread was controlled by the strength of its weakest fibres. With the help of R. A. Fisher, Tippet obtained three asymptotic limits describing the distributions of extremes assuming independent variables. Emil Julius Gumbel codified this theory in his 1958 book Statistics of Extremes, including the Gumbel distributions that bear his name. These results can be extended to allow for slight correlations between variables, but the classical theory does not extend to strong correlations of the order of the variance. One universality class of particular interest is that of log-correlated fields, where the correlations decay logarithmically with the distance.

A summary of historically important publications relating to extreme value theory can be found in the List of publications in statistics.

Univariate theory

Let ${\displaystyle X_{1},\dots ,X_{n}}$ be a sequence of independent and identically distributed random variables with cumulative distribution function F and let ${\displaystyle M_{n}=\max(X_{1},\dots ,X_{n})}$ denote the maximum.

In theory, the exact distribution of the maximum can be derived:

${\displaystyle {\begin{aligned}\Pr(M_{n}\leq z)&=\Pr(X_{1}\leq z,\dots ,X_{n}\leq z)\\&=\Pr(X_{1}\leq z)\cdots \Pr(X_{n}\leq z)=(F(z))^{n}.\end{aligned}}}$

The associated indicator function ${\displaystyle I_{n}=I(M_{n}>z)}$ is a Bernoulli process with a success probability ${\displaystyle p(z)=1-(F(z))^{n}}$ that depends on the magnitude ${\displaystyle z}$ of the extreme event. The number of extreme events within ${\displaystyle n}$ trials thus follows a binomial distribution and the number of trials until an event occurs follows a geometric distribution with expected value and standard deviation of the same order ${\displaystyle O(1/p(z))}$.

In practice, we might not have the distribution function ${\displaystyle F}$ but the Fisher–Tippett–Gnedenko theorem provides an asymptotic result. If there exist sequences of constants ${\displaystyle a_{n}>0}$ and ${\displaystyle b_{n}\in \mathbb {R} }$ such that

${\displaystyle \Pr\{(M_{n}-b_{n})/a_{n}\leq z\}\rightarrow G(z)}$

as ${\displaystyle n\rightarrow \infty }$ then

${\displaystyle G(z)\propto \exp \left[-(1+\zeta z)^{-1/\zeta }\right]}$

where ${\displaystyle \zeta }$ depends on the tail shape of the distribution. When normalized, G belongs to one of the following non-degenerate distribution families:

Weibull law: ${\displaystyle G(z)={\begin{cases}\exp \left\{-\left(-\left({\frac {z-b}{a}}\right)\right)^{\alpha }\right\}&z<b\\1&z\geq b\end{cases}}}$ when the distribution of ${\displaystyle M_{n}}$ has a light tail with finite upper bound. Also known as Type 3.

Gumbel law: ${\displaystyle G(z)=\exp \left\{-\exp \left(-\left({\frac {z-b}{a}}\right)\right)\right\}{\text{ for }}z\in \mathbb {R} .}$ when the distribution of ${\displaystyle M_{n}}$ has an exponential tail. Also known as Type 1

Fréchet Law: ${\displaystyle G(z)={\begin{cases}0&z\leq b\\\exp \left\{-\left({\frac {z-b}{a}}\right)^{-\alpha }\right\}&z>b.\end{cases}}}$ when the distribution of ${\displaystyle M_{n}}$ has a heavy tail (including polynomial decay). Also known as Type 2.

In all cases, ${\displaystyle \alpha >0}$.

Multivariate theory

Extreme value theory in more than one variable introduces additional issues that have to be addressed. One problem that arises is that one must specify what constitutes an extreme event. Although this is straightforward in the univariate case, there is no unambiguous way to do this in the multivariate case. The fundamental problem is that although it is possible to order a set of real-valued numbers, there is no natural way to order a set of vectors.

As an example, in the univariate case, given a set of observations ${\displaystyle x_{i}}$ it is straightforward to find the most extreme event simply by taking the maximum (or minimum) of the observations. However, in the bivariate case, given a set of observations ${\displaystyle (x_{i},y_{i})}$, it is not immediately clear how to find the most extreme event. Suppose that one has measured the values ${\displaystyle (3,4)}$ at a specific time and the values ${\displaystyle (5,2)}$ at a later time. Which of these events would be considered more extreme? There is no universal answer to this question.

Another issue in the multivariate case is that the limiting model is not as fully prescribed as in the univariate case. In the univariate case, the model (GEV distribution) contains three parameters whose values are not predicted by the theory and must be obtained by fitting the distribution to the data. In the multivariate case, the model not only contains unknown parameters, but also a function whose exact form is not prescribed by the theory. However, this function must obey certain constraints.

As an example of an application, bivariate extreme value theory has been applied to ocean research.