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A heat wave is a period of excessively hot weather, which may be accompanied by high humidity, especially in oceanic climate countries. While definitions vary,a heat wave is usually measured relative to the usual weather in the area and relative to normal temperatures for the season. Temperatures that people from a hotter climate consider normal can be termed a heat wave in a cooler area if they are outside the normal climate pattern for that area.
Humidity is the amount of water vapour present in air. Water vapour, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present. The amount of water vapour needed to achieve saturation increases as the temperature increases. As the temperature of a parcel of air decreases it will eventually reach the saturation point without adding or losing water mass. The amount of water vapour contained within a parcel of air can vary significantly. For example, a parcel of air near saturation may contain 28 grams of water per cubic metre of air at 30 °C, but only 8 grams of water per cubic metre of air at 8 °C.
An oceanic climate, also known as a marine climate or maritime climate, is the Köppen classification of climate typical of west coasts in higher middle latitudes of continents, and generally features mild summers and mild winters, with a relatively narrow annual temperature range and few extremes of temperature, with the exception for transitional areas to continental, subarctic and highland climates. Oceanic climates are defined as having a monthly mean temperature below 22 °C (72 °F) in the warmest month, and above 0 °C (32 °F) in the coldest month.
Climate is defined as the average state of everyday's weather condition over a period of 30 years. It is measured by assessing the patterns of variation in temperature, humidity, atmospheric pressure, wind, precipitation, atmospheric particle count and other meteorological variables in a given region over long periods of time. Climate differs from weather, in that weather only describes the short-term conditions of these variables in a given region.
The term is applied both to hot weather variations and to extraordinary spells of hot which may occur only once a century. Severe heat waves have caused catastrophic crop failures, thousands of deaths from hyperthermia, and widespread power outages due to increased use of air conditioning. A heat wave is considered extreme weather, and a danger because heat and sunlight may overheat the human body. Heat waves can usually be detected using forecasting instruments so that a warning call can be issued.
Hyperthermia is a condition where an individual's body temperature is elevated beyond normal due to failed thermoregulation. The person's body produces or absorbs more heat than it dissipates. When extreme temperature elevation occurs, it becomes a medical emergency requiring immediate treatment to prevent disability or death.
Extreme weather includes unexpected, unusual, unpredictable, 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. In recent years some extreme weather events have been attributed to human-induced global warming, with studies indicating an increasing threat from extreme weather in the future.
Forecasting is the process of making predictions of the future based on past and present data and most commonly by analysis of trends. A commonplace example might be estimation of some variable of interest at some specified future date. Prediction is a similar, but more general term. Both might refer to formal statistical methods employing time series, cross-sectional or longitudinal data, or alternatively to less formal judgmental methods. Usage can differ between areas of application: for example, in hydrology the terms "forecast" and "forecasting" are sometimes reserved for estimates of values at certain specific future times, while the term "prediction" is used for more general estimates, such as the number of times floods will occur over a long period.
A definition based on Frich et al.'s Heat Wave Duration Index is that a heat wave occurs when the daily maximum temperature of more than five consecutive days exceeds the average maximum temperature by 5 °C (9 °F ), the normal period being 1961–1990.
The Celsius scale, also known as the centigrade scale, is a temperature scale used by the International System of Units (SI). As an SI derived unit, it is used by all countries except the United States, the Bahamas, Belize, the Cayman Islands and Liberia. It is named after the Swedish astronomer Anders Celsius (1701–1744), who developed a similar temperature scale. The degree Celsius can refer to a specific temperature on the Celsius scale or a unit to indicate a difference between two temperatures or an uncertainty. Before being renamed to honor Anders Celsius in 1948, the unit was called centigrade, from the Latin centum, which means 100, and gradus, which means steps.
The Fahrenheit scale is a temperature scale based on one proposed in 1724 by Dutch–German–Polish physicist Daniel Gabriel Fahrenheit (1686–1736). It uses the degree Fahrenheit as the unit. Several accounts of how he originally defined his scale exist. The lower defining point, 0 °F, was established as the freezing temperature of a solution of brine made from equal parts of ice, water and salt. Further limits were established as the melting point of ice (32 °F) and his best estimate of the average human body temperature. The scale is now usually defined by two fixed points: the temperature at which water freezes into ice is defined as 32 °F, and the boiling point of water is defined to be 212 °F, a 180 °F separation, as defined at sea level and standard atmospheric pressure.
A formal, peer-reviewed definition from the Glossary of Meteorology is:
Peer review is the evaluation of work by one or more people with similar competences as the producers of the work (peers). It functions as a form of self-regulation by qualified members of a profession within the relevant field. Peer review methods are used to maintain quality standards, improve performance, and provide credibility. In academia, scholarly peer review is often used to determine an academic paper's suitability for publication. Peer review can be categorized by the type of activity and by the field or profession in which the activity occurs, e.g., medical peer review.
The World Meteorological Organization, defines a heat wave as 5 or more consecutive days of prolonged heat in which the daily maximum temperature is higher than the average maximum temperature by 9 °F or more.However, some nations have come up with their own criteria to define a heat wave.
The World Meteorological Organization (WMO) is an intergovernmental organization with a membership of 192 Member States and Territories. Its current Secretary-General is Petteri Taalas and the President of the World Meteorological Congress, its supreme body, is David Grimes. The Organization is headquartered in Geneva, Switzerland.
In the Netherlands, a heat wave is defined as a period of at least 5 consecutive days in which the maximum temperature in De Bilt exceeds 25 °C (77 °F), provided that on at least 3 days in this period the maximum temperature in De Bilt exceeds 30 °C (86 °F). This definition of a heat wave is also used in Belgium and Luxembourg.
The Netherlands, also commonly known as Holland, is a country located mainly in Northwestern Europe. The European portion of the Netherlands consists of twelve separate provinces that border Germany to the east, Belgium to the south, and the North Sea to the northwest, with maritime borders in the North Sea with Belgium, Germany and the United Kingdom. Together with three island territories in the Caribbean Sea—Bonaire, Sint Eustatius and Saba— it forms a constituent country of the Kingdom of the Netherlands. The official language is Dutch, but a secondary official language in the province of Friesland is West Frisian.
De Bilt is a municipality and a town in the Netherlands, in the province of Utrecht. De Bilt had a population of 42,815 in 2017 and is the seat of the headquarters of the Royal Dutch Meteorological Institute, KNMI.
Belgium, officially the Kingdom of Belgium, is a country in Western Europe. It is bordered by the Netherlands to the north, Germany to the east, Luxembourg to the southeast, France to the southwest, and the North Sea to the northwest. It covers an area of 30,688 square kilometres (11,849 sq mi) and has a population of more than 11.4 million. The capital and largest city is Brussels; other major cities are Antwerp, Ghent, Charleroi and Liège.
In Denmark, a national heat wave (hedebølge) is defined as a period of at least 3 consecutive days of which period the average maximum temperature across more than fifty percent of the country exceeds 28 °C (82.4 °F) – the Danish Meteorological Institute further defines a "warmth wave" (varmebølge) when the same criteria are met for a 25 °C (77.0 °F) temperature, while in Sweden, a heat wave is defined as at least 5 days in a row with a daily high exceeding 25 °C (77.0 °F).
In the United States, definitions also vary by region; however, a heat wave is usually defined as a period of at least two or more days of excessively hot weather. 90 °F (32.2 °C), but not always as this ties in with humidity levels to determine a heat index threshold. The same does not apply to drier climates. A heat storm is a Californian term for an extended heat wave. Heat storms occur when the temperature reaches 100 °F (37.8 °C) for three or more consecutive days over a wide area (tens of thousands of square miles). The National Weather Service issues heat advisories and excessive heat warnings when unusual periods of hot weather are expected.In the Northeast, a heat wave is typically defined as three consecutive days where the temperature reaches or exceeds
In Adelaide, South Australia, a heat wave is defined as five consecutive days at or above 35 °C (95 °F), or three consecutive days at or over 40 °C (104 °F). The Australian Bureau of Meteorology defines a heat wave as "three days or more of maximum and minimum temperatures that are unusual for the location". Until the introduction of this new Pilot Heatwave Forecast there was no national definition that described heatwave or measures of heatwave severity.
In the United Kingdom, the Met Office operates a Heat Health Watch system which places each Local Authority region into one of four levels. Heatwave conditions are defined by the maximum daytime temperature and minimum nighttime temperature rising above the threshold for a particular region. The length of time spent above that threshold determines the particular level. Level 1 is normal summer conditions. Level 2 is reached when there is a 60% or higher risk that the temperature will be above the threshold levels for two days and the intervening night. Level 3 is triggered when the temperature has been above the threshold for the preceding day and night, and there is a 90% or higher chance that it will stay above the threshold in the following day. Level 4 is triggered if conditions are more severe than those of the preceding three levels. Each of the first three levels is associated with a particular state of readiness and response by the social and health services, and Level 4 is associated with more widespread response.
A more general indicator that allows comparing heat waves in different regions of the World, characterized by different climates, has been recently developed.This was used to estimate heat waves occurrence at the global scale from 1901 to 2010, finding a substantial and sharp increase in the amount of affected areas in the last two decades.
Heat waves form when high pressure aloft (from 10,000–25,000 feet (3,000–7,600 metres)) strengthens and remains over a region for several days up to several weeks. This is common in summer (in both Northern and Southern Hemispheres) as the jet stream 'follows the sun'. On the equator side of the jet stream, in the upper layers of the atmosphere, is the high pressure area.
Summertime weather patterns are generally slower to change than in winter. As a result, this upper level high pressure also moves slowly. Under high pressure, the air subsides (sinks) toward the surface, warming and drying adiabatically. This warmer sinking air creates a high level inversion that acts as a dome capping the atmosphere, inhibiting convection, thereby trapping high humidity warm air below it. Typically, convection is present along the periphery of the cap where the pressure becomes less. This peripheral convection, however, can add to the high pressure dome by ventilating the upper level outflow of the thunderstorms into it. The end result is a continual build-up of heat at the surface that people experience as a heat wave.
In the Eastern United States a heat wave can occur when a high pressure system originating in the Gulf of Mexico becomes stationary just off the Atlantic Seaboard (typically known as a Bermuda High). Hot humid air masses form over the Gulf of Mexico and the Caribbean Sea while hot dry air masses form over the desert Southwest and northern Mexico. The SW winds on the back side of the High continue to pump hot, humid Gulf air northeastward resulting in a spell of hot and humid weather for much of the Eastern States.
In the Western Cape Province of South Africa, a heat wave can occur when a low pressure offshore and high pressure inland air combine to form a Bergwind. The air warms as it descends from the Karoo interior, and the temperature will rise about 10 °C from the interior to the coast. Humidities are usually very low, and the temperatures can be over 40 °C in summer. The highest official temperatures recorded in South Africa (51.5 °C) was recorded one summer during a bergwind occurring along the Eastern Cape coastline.
Global warming boosts the probability of extreme weather events, like heat waves, far more than it boosts more moderate events.
|80 °F (27 °C)||82 °F (28 °C)||84 °F (29 °C)||86 °F (30 °C)||88 °F (31 °C)||90 °F (32 °C)||92 °F (33 °C)||94 °F (34 °C)||96 °F (36 °C)||98 °F (37 °C)||100 °F (38 °C)||102 °F (39 °C)||104 °F (40 °C)||106 °F (41 °C)||108 °F (42 °C)||110 °F (43 °C)|
|40%||80 °F (27 °C)||81 °F (27 °C)||83 °F (28 °C)||85 °F (29 °C)||88 °F (31 °C)||91 °F (33 °C)||94 °F (34 °C)||97 °F (36 °C)||101 °F (38 °C)||105 °F (41 °C)||109 °F (43 °C)||114 °F (46 °C)||119 °F (48 °C)||124 °F (51 °C)||130 °F (54 °C)||136 °F (58 °C)|
|45%||80 °F (27 °C)||82 °F (28 °C)||84 °F (29 °C)||87 °F (31 °C)||89 °F (32 °C)||93 °F (34 °C)||96 °F (36 °C)||100 °F (38 °C)||104 °F (40 °C)||109 °F (43 °C)||114 °F (46 °C)||119 °F (48 °C)||124 °F (51 °C)||130 °F (54 °C)||137 °F (58 °C)|
|50%||81 °F (27 °C)||83 °F (28 °C)||85 °F (29 °C)||88 °F (31 °C)||91 °F (33 °C)||95 °F (35 °C)||99 °F (37 °C)||103 °F (39 °C)||108 °F (42 °C)||113 °F (45 °C)||118 °F (48 °C)||124 °F (51 °C)||131 °F (55 °C)||137 °F (58 °C)|
|55%||81 °F (27 °C)||84 °F (29 °C)||86 °F (30 °C)||89 °F (32 °C)||93 °F (34 °C)||97 °F (36 °C)||101 °F (38 °C)||106 °F (41 °C)||112 °F (44 °C)||117 °F (47 °C)||124 °F (51 °C)||130 °F (54 °C)||137 °F (58 °C)|
|60%||82 °F (28 °C)||84 °F (29 °C)||88 °F (31 °C)||91 °F (33 °C)||95 °F (35 °C)||100 °F (38 °C)||105 °F (41 °C)||110 °F (43 °C)||116 °F (47 °C)||123 °F (51 °C)||129 °F (54 °C)||137 °F (58 °C)|
|65%||82 °F (28 °C)||85 °F (29 °C)||89 °F (32 °C)||93 °F (34 °C)||98 °F (37 °C)||103 °F (39 °C)||108 °F (42 °C)||114 °F (46 °C)||121 °F (49 °C)||128 °F (53 °C)||136 °F (58 °C)|
|70%||83 °F (28 °C)||86 °F (30 °C)||90 °F (32 °C)||95 °F (35 °C)||100 °F (38 °C)||105 °F (41 °C)||112 °F (44 °C)||119 °F (48 °C)||126 °F (52 °C)||134 °F (57 °C)|
|75%||84 °F (29 °C)||88 °F (31 °C)||92 °F (33 °C)||97 °F (36 °C)||103 °F (39 °C)||109 °F (43 °C)||116 °F (47 °C)||124 °F (51 °C)||132 °F (56 °C)|
|80%||84 °F (29 °C)||89 °F (32 °C)||94 °F (34 °C)||100 °F (38 °C)||106 °F (41 °C)||113 °F (45 °C)||121 °F (49 °C)||129 °F (54 °C)|
|85%||85 °F (29 °C)||90 °F (32 °C)||96 °F (36 °C)||102 °F (39 °C)||110 °F (43 °C)||117 °F (47 °C)||126 °F (52 °C)||135 °F (57 °C)|
|90%||86 °F (30 °C)||91 °F (33 °C)||98 °F (37 °C)||105 °F (41 °C)||113 °F (45 °C)||122 °F (50 °C)||131 °F (55 °C)|
|95%||86 °F (30 °C)||93 °F (34 °C)||100 °F (38 °C)||108 °F (42 °C)||117 °F (47 °C)||127 °F (53 °C)|
|100%||87 °F (31 °C)||95 °F (35 °C)||103 °F (39 °C)||112 °F (44 °C)||121 °F (49 °C)||132 °F (56 °C)|
The heat index (as shown in the table above) is a measure of how hot it feels when relative humidity is factored with the actual air temperature. Hyperthermia, also known as heat stroke, becomes commonplace during periods of sustained high temperature and humidity. Older adults, very young children, and those who are sick or overweight are at a higher risk for heat-related illness. The chronically ill and elderly are often taking prescription medications (e.g., diuretics, anticholinergics, antipsychotics, and antihypertensives) that interfere with the body's ability to dissipate heat.
Heat edema presents as a transient swelling of the hands, feet, and ankles and is generally secondary to increased aldosterone secretion, which enhances water retention. When combined with peripheral vasodilation and venous stasis, the excess fluid accumulates in the dependent areas of the extremities. The heat edema usually resolves within several days after the patient becomes acclimated to the warmer environment. No treatment is required, although wearing support stockings and elevating the affected legs will help minimize the edema.
Heat rash, also known as prickly heat, is a maculopapular rash accompanied by acute inflammation and blocked sweat ducts. The sweat ducts may become dilated and may eventually rupture, producing small pruritic vesicles on an erythematous base. Heat rash affects areas of the body covered by tight clothing. If this continues for a duration of time it can lead to the development of chronic dermatitis or a secondary bacterial infection. Prevention is the best therapy. It is also advised to wear loose-fitting clothing in the heat. However, once heat rash has developed, the initial treatment involves the application of chlorhexidine lotion to remove any desquamated skin. The associated itching may be treated with topical or systemic antihistamines. If infection occurs a regimen of antibiotics is required.
Heat cramps are painful, often severe, involuntary spasms of the large muscle groups used in strenuous exercise. Heat cramps tend to occur after intense exertion. They usually develop in people performing heavy exercise while sweating profusely and replenishing fluid loss with non-electrolyte containing water. This is believed to lead to hyponatremia that induces cramping in stressed muscles. Rehydration with salt-containing fluids provides rapid relief. Patients with mild cramps can be given oral .2% salt solutions, while those with severe cramps require IV isotonic fluids. The many sport drinks on the market are a good source of electrolytes and are readily accessible.
Heat syncope is related to heat exposure that produces orthostatic hypotension. This hypotension can precipitate a near-syncopal episode. Heat syncope is believed to result from intense sweating, which leads to dehydration, followed by peripheral vasodilation and reduced venous blood return in the face of decreased vasomotor control. Management of heat syncope consists of cooling and rehydration of the patient using oral rehydration therapy (sport drinks) or isotonic IV fluids. People who experience heat syncope should avoid standing in the heat for long periods of time. They should move to a cooler environment and lie down if they recognize the initial symptoms. Wearing support stockings and engaging in deep knee-bending movements can help promote venous blood return.
Heat exhaustion is considered by experts to be the forerunner of heat stroke (hyperthermia). It may even resemble heat stroke, with the difference being that the neurologic function remains intact. Heat exhaustion is marked by excessive dehydration and electrolyte depletion. Symptoms may include diarrhea, headache, nausea and vomiting, dizziness, tachycardia, malaise, and myalgia. Definitive therapy includes removing patients from the heat and replenishing their fluids. Most patients will require fluid replacement with IV isotonic fluids at first. The salt content is adjusted as necessary once the electrolyte levels are known. After discharge from the hospital, patients are instructed to rest, drink plenty of fluids for 2–3 hours, and avoid the heat for several days. If this advice is not followed it may then lead to heat stroke.
One public health measure taken during heat waves is the setting-up of air-conditioned public cooling centers.
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Heat waves are the most lethal type of weather phenomenon in the United States. Between 1992 and 2001, deaths from excessive heat in the United States numbered 2,190, compared with 880 deaths from floods and 150 from hurricanes.The average annual number of fatalities directly attributed to heat in the United States is about 400. The 1995 Chicago heat wave, one of the worst in US history, led to approximately 739 heat-related deaths over a period of five days. Eric Klinenberg has noted that in the United States, the loss of human life in hot spells in summer exceeds that caused by all other weather events combined, including lightning, rain, floods, hurricanes, and tornadoes. Despite the dangers, Scott Sheridan, professor of geography at Kent State University, found that less than half of people 65 and older abide by heat-emergency recommendations like drinking lots of water. In his study of heat-wave behavior, focusing particularly on seniors in Philadelphia, Phoenix, Toronto, and Dayton, Ohio, he found that people over 65 "don't consider themselves seniors." One of his older respondents said: "Heat doesn't bother me much, but I worry about my neighbors."
According to the Agency for Health care Research and Quality, about 6,200 Americans are hospitalized each summer due to excessive heat, and those at highest risk are poor, uninsured or elderly.More than 70,000 Europeans died as a result of the 2003 European heat wave.
Our concern now is focusing on predicting the future likelihood of heat waves and their severity. In addition, because in most of the world most of those suffering the impacts of a heat wave will be inside a building, and this will modify the temperatures they are exposed to, there is the need to link climate models to building models. This means producing example time series of future weather.Other work has shown that future mortality due to heat waves could be reduced if buildings were better designed to modify the internal climate, or if the occupants were better educated about the issues, so they can take action in time.
The number of heat fatalities is likely highly underreported due to a lack of reports and misreports.Part of the mortality observed during a heat wave, however, can be attributed to a so-called "harvesting effect", a term for a short-term forward mortality displacement. It has been observed that for some heat waves, there is a compensatory decrease in overall mortality during the subsequent weeks after a heat wave. Such compensatory reductions in mortality suggest that heat affects especially those so ill that they "would have died in the short term anyway".
Another explanation for underreporting is the social attenuation in most contexts of heat waves as a health risk. As shown by the deadly French heat wave in 2003, heat wave dangers result from the intricate association of natural and social factors.
In addition to physical stress, excessive heat causes psychological stress, to a degree which affects performance, and is also associated with an increase in violent crime.High temperatures are associated with increased conflict both at the interpersonal level and at the societal level. In every society, crime rates go up when temperatures go up, particularly violent crimes such as assault, murder, and rape. Furthermore, in politically unstable countries, high temperatures are an aggravating factor that lead toward civil wars.
Additionally, high temperatures have a significant effect on income. A study of counties in the United States found that economic productivity of individual days declines by about 1.7% for each degree Celsius above 15 °C (59 °F).
Abnormally hot temperatures can cause electricity demand to increase during the peak summertime hours of 4 to 7 p.m. when air conditioners are straining to overcome the heat. If a hot spell extends to three days or more, however, nighttime temperatures do not cool down, and the thermal mass in homes and buildings retains the heat from previous days. This heat build-up causes air conditioners to turn on earlier and to stay on later in the day. As a result, available electricity supplies are challenged during a higher, wider, peak electricity consumption period.[ citation needed ]
Heat waves often lead to electricity spikes due to increased air conditioning use, which can create power outages, exacerbating the problem. During the 2006 North American heat wave, thousands of homes and businesses went without power, especially in California. In Los Angeles, electrical transformers failed, leaving thousands without power for as long as five days.The 2009 South Eastern Australia Heat Wave caused the city of Melbourne, Australia to experience some major power disruptions which left over half a million people without power as the heat wave blew transformers and overloaded a power grid.
If a heat wave occurs during a drought, which dries out vegetation, it can contribute to bushfires and wildfires. During the disastrous heat wave that struck Europe in 2003, fires raged through Portugal, destroying over 3,010 square kilometres (1,160 sq mi) or 301,000 hectares (740,000 acres) of forest and 440 square kilometres (170 sq mi) or 44,000 hectares (110,000 acres) of agricultural land and causing an estimated €1 billion worth of damage. High end farmlands have irrigation systems to back up crops with.
Heat waves can and do cause roads and highways to buckle and melt,water lines to burst, and power transformers to detonate, causing fires. See the 2006 North American heat wave article about heat waves causing physical damage.
Heat waves can also damage rail roads, such as buckling and kinking rails, which can lead to slower traffic, delays, and even cancellations of service when rails are too dangerous to traverse by trains. Sun kinking is caused when certain types of rail design like short section rails welded together or fish plate rails expand and push on other sections of rail causing them to warp and kink. Sun kinking can be a serious problem in hotter climates like Southern USA, parts of Canada, the Middle East, etc.
In the 2013 heatwave in England, gritters (normally only seen in snow) were sent out to grit melting tarmac roads.[ citation needed ]
Climate models reveal that future heat waves will have a more intense geologic pattern.The famous heat wave events of Chicago in 1995 and the European heat wave of 2003 regions will experience longer, more frequent and more intense heat waves in the latter 21st century. Heat waves today in Europe and North America happen parallel to the conditions of atmospheric circulation. Increased anthropogenic activities causing increased greenhouse gas emissions show that heat waves will be more severe.
Heat waves and droughts as a result, minimize ecosystem carbon uptake.Carbon uptake is also known as carbon sequestration. Extreme heat wave events are predicted to happen with increased global warming, which puts stress on ecosystems. Stress on ecosystems due to future intensified heat waves will reduce biological productivity. This will cause changes in the ecosystem's carbon cycle feedback because there will be less vegetation to hold the carbon from the atmosphere, which will only contribute more to atmospheric warming.
The 1995 Chicago heat wave was a heat wave which led to 739 heat-related deaths in Chicago over a period of five days. Most of the victims of the heat wave were elderly poor residents of the city, who could not afford air conditioning and did not open windows or sleep outside for fear of crime. The heat wave also heavily impacted the wider Midwestern region, with additional deaths in both St. Louis, Missouri and Milwaukee, Wisconsin.
The 2003 European heat wave led to the hottest summer on record in Europe since at least 1540. France was hit especially hard. The heat wave led to health crises in several countries and combined with drought to create a crop shortfall in parts of Southern Europe. Peer-reviewed analysis places the European death toll at more than 70,000. The predominant heat was recorded in July and August, partly a result of the western European seasonal lag from the maritime influence of the Atlantic warm waters in combination with hot continental air and strong southerly winds.
Adelaide has a Mediterranean climate, with cool to mild winters with moderate rainfall and warm to hot, generally dry summers.
The 2006 European heat wave was a period of exceptionally hot weather that arrived at the end of June 2006 in certain European countries. The United Kingdom, France, Belgium, the Netherlands, Luxembourg, Italy, Poland, the Czech Republic, Hungary, Germany and western parts of Russia were most affected. Several records were broken. In the Netherlands, Belgium, Germany, Ireland and the United Kingdom, July 2006 was the warmest month since official measurements began.
The climate of Sydney is humid subtropical, shifting from mild and cool in winter to warm and hot in the summer, with no extreme seasonal differences as the weather is moderated by proximity to the ocean, although more contrasting temperatures are recorded in the inland western suburbs. Despite the fact that there is no distinct dry or wet season, rainfall peaks in the first half of the year and is at its lowest in the second half. Precipitation varies across the region, with areas adjacent to the coast being the wettest. The city receives around 20 thunderstorms per year.
The climate of Delhi is an overlap between monsoon-influenced humid subtropical and semi-arid, with high variation between summer and winter temperatures and precipitation. Delhi's version of a humid subtropical climate is markedly different from many other humid subtropical cities such as Sao Paulo, New Orleans and Brisbane in that the city features dust storms and wildfire haze due to its semi-arid climate.
Australia's climate is governed mostly by its size and by the hot, sinking air of the subtropical high pressure belt. This moves north and south with the seasons. The climate is variable, with frequent droughts lasting several seasons, thought to be caused in part by the El Niño-Southern Oscillation. Australia has a wide variety of climates due to its large geographical size. The largest part of Australia is desert or semi-arid. Only the south-east and south-west corners have a temperate climate and moderately fertile soil. The northern part of the country has a tropical climate, varying between tropical rainforests, grasslands and desert.
The 2009 southeastern Australia heat wave was a heat wave that commenced in late January and led to record-breaking prolonged high temperatures in the region. The heat wave is considered one of the, if not the, most extreme in the region's history. During the heat wave, fifty separate locations set various records for consecutive, highest daytime and overnight temperatures. The highest temperature recorded during the heat wave was 48.8 °C (119.8 °F) in Hopetoun, Victoria, a record for the state. Many locations through the region recorded all-time high temperatures including capital cities Adelaide, which reached its third-highest temperature, 45.7 °C (114.3 °F), and Melbourne, which recorded its highest-ever temperature on record, 46.4 °C (115.5 °F). Both cities broke records for the most consecutive days over 40 °C (104 °F), while Mildura, Victoria recorded an all-time record twelve consecutive days over 43 °C (109 °F).
A wake low, or wake depression, is a mesoscale low-pressure area which trails the mesoscale high following a squall line. Due to the subsiding warm air associated with the systems formation, clearing skies are associated with the wake low. Once difficult to detect in surface weather observations due to their broad spacing, the formation of mesoscale weather station networks, or mesonets, has increased their detection. Severe weather, in the form of high winds, can be generated by the wake low when the pressure difference between the mesohigh preceding it and the wake low is intense enough. When the squall line is in the process of decay, heat bursts can be generated near the wake low. Once new thunderstorm activity along the squall line concludes, the wake low associated with it weakens in tandem.
The 1906 United Kingdom heat wave occurred across Great Britain in the months of August and September. The heat wave had a comparable intensity to the 1990 heat wave. From 31 August to 3 September, the temperature in the UK exceeded 32 °C (90 °F) consecutively over most of the UK on these four days. In September, CET Central England and Birmingham recorded a highest temperature of 31.5 °C (88.7 °F), and Oxford recorded a highest temperature of 33.1 °C (91.6 °F), the Oxford high surpassed in 1911 with a temperature of 33.4 °C (92.1 °F).
Egypt essentially has a hot desert climate. The climate is generally extremely dry all over the country except on the northern Mediterranean coast which receives rainfall in winter. In addition to rarity of rain, extreme heat during summer months is also a general climate feature of Egypt although daytime temperatures are more moderated along the northern coast.
The 2010 Northern Hemisphere summer heat waves included severe heat waves that impacted most of the United States, Kazakhstan, Mongolia, China, Hong Kong, North Africa and the European continent as a whole, along with parts of Canada, Russia, Indochina, South Korea and Japan during May, June, July, and August 2010. The first phase of the global heatwaves was caused by a moderate El Niño event, which lasted from June 2009 to May 2010. The first phase lasted only from April 2010 to June 2010, and caused only moderate above average temperatures in the areas affected. But it also set new record high temperatures for most of the area affected, in the Northern Hemisphere. The second phase was caused by a very strong La Niña event, which lasted from June 2010 to June 2011. According to meteorologists, the 2010–11 La Niña event was one of the strongest La Niña events ever observed. That same La Niña event also had devastating effects in the Eastern states of Australia. The second phase lasted from June 2010 to October 2010, caused severe heat waves, and multiple record-breaking temperatures. The heatwaves began on April 2010, when strong anticyclones began to develop, over most of the affected regions, in the Northern Hemisphere. The heatwaves ended in October 2010, when the powerful anticyclones over most of the affected areas dissipated.
The Australian summer of 2012–2013, known as the Angry Summer or Extreme Summer, resulted in 123 weather records being broken over a 90-day period, including the hottest day ever recorded for Australia as a whole, the hottest January on record, the hottest summer average on record, and a record seven days in a row when the whole continent averaged above 39°C (102°F). Single-day temperature records were broken in dozens of towns and cities, as well as single-day rainfall records, and several rivers flooded to new record highs.
The 2013 heat wave in the United Kingdom and Ireland was a period of unusually hot weather primarily in July 2013, with isolated warm days in June and August. A prolonged high pressure system over Britain and Ireland caused higher than average temperatures for 19 consecutive days in July, reaching 33.5°C at Heathrow and Northolt. Following a brief period of cooler weather at the end of July, temperatures temporarily rose again, peaking at 34.1°C on 1 August in the United Kingdom, the warmest the country had seen since July 2006, and 31.0°C in Ireland. At 19 days, the July heatwave was the longest continuous period of hot weather in the UK since August 1997.
The 1995 United Kingdom and Ireland heat wave was a severe weather event that occurred between late July and late August, and was part one of the warmest summers recorded in the UK, and one of the warmest Augusts ever recorded in many locations around the UK, as well as being one of the driest summers ever recorded in the UK, with many weather stations having the Summer of 1995 drier than, or comparable with the Summer of 1976. Ireland was also widely affected by the heatwave with temperatures reaching over 30 °C (86 °F) in some locations, as well as exceptionally low rainfall throughout the summer.
The 2018 British Isles heat wave was a period of unusually hot weather that took place in June, July and August. It led to record-breaking temperatures in the UK and Ireland. It caused widespread drought, hosepipe bans, crop failures, and a number of wildfires. These wildfires worst affected northern moorland areas around the Greater Manchester region, the largest was at Saddleworth Moor and another was at Winter Hill, together these burned over 14 square miles (36 km2) of land over a period of nearly a month.
The 2018 European drought and heat wave was a period of unusually hot weather that led to record-breaking temperatures and wildfires in many parts of Europe during the spring and summer of 2018. It is part of a larger heat wave affecting the northern hemisphere, caused in part by the jet stream being weaker than usual, allowing hot high-pressure air to linger in the same place. According to the European Drought Observatory, most of the areas affected by drought are across northern and central Europe.
In 2018, several heat waves with temperatures far above the long-time average were recorded in the Northern Hemisphere: The earth's average surface temperature in 2018 was the fourth highest in the 140 years of record keeping. It is assumed that the jet stream is slowing down, trapping cloudless, windless and extremely hot regions of high pressure. The jet stream anomalies could be caused by polar amplification, one of the observed effects of global warming.