A heat wave
is prolonged period of excessively hot weather, which may be accompanied by high humidity. There is no universal definition of a heat wave; [1] the term is relative to the usual weather in the area. 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. [2]
The term is applied both to routine weather variations and to extraordinary spells of heat 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.
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HEATWAVE TICKETS
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Definitions
The definition recommended by the
World Meteorological Organization is when the daily maximum temperature of more than five consecutive days exceeds the average maximum temperature by 5 Celsius degrees (9 Fahrenheit degrees), the normal period being 1961–1990.
[3]
A formal,
peer-reviewed definition from the
Glossary of Meteorology
is:
[4]
A period of abnormally and uncomfortably hot and usually humid weather.
: To be a heat wave such a period should last at least one day, but conventionally it lasts from several days to several weeks. In 1900, A. T. Burrows more rigidly defined a “hot wave” as a spell of three or more days on each of which the maximum shade temperature reaches or exceeds . More realistically, the comfort criteria for any one region are dependent upon the normal conditions of that region.
A
heat storm is a Californian term for an extended heat wave. Heat storms occur when the temperature reaches for three or more consecutive days over a wide area (tens of thousands of square miles).
In the
Netherlands, a heat wave is defined as period of at least 5 consecutive days in which the maximum temperature in
De Bilt exceeds , provided that on at least 3 days in this period the maximum temperature in De Bilt exceeds . This definition of a heat wave is also used in
Belgium and
Luxembourg.
In
Denmark a heat wave 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.
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.
[5] The
National Weather Service issues
heat advisories and
excessive heat warnings when unusual periods of hot weather are expected.
Incidence
Heat waves often occur during the
Dog Days of summer; indeed the
French term
canicule
, denoting the general phenomenon of a heat wave, derives from the
Italian canicula
applied to the star
Sirius, also known as the "Dog Star."
[6]
Some regions of the
globe are more susceptible to heat waves than others, typically inland desert, semidesert, and
Mediterranean-type climates.
According to climatologist
David Jones the likelihood of heat waves occurring is expected to increase with
global warming.
[7]
How they occur
In the summer in warm climates, an area of high pressure with little or no rain or clouds, the air and ground easily heats to excess. A static high pressure area can impose a very persistent heat wave.
The position of the
jet stream allows air on one side to be considerably warmer than the other side. Heat waves are far more common and more severe on the warm side and at times an unusual position of the jet stream places unusual warmth in an unusual place for hot weather, and imposes a heat wave.
El Niño and La Niña (opposite reaction to El Niño) can severely disrupt the positions of the jet streams.
thumb after the
2003 European heat waveLarge desert zones and dry areas are more likely to get extreme heat because there is rarely any high cloud cover with very low humidity.
Winds from hot deserts typically push hot, dry air towards areas normally cooler than during a heat wave. During the summer an area that has no geographic features that might cool winds that originate in the hot deserts get little mitigation, especially near the summer solstice when long days and a high sun would create warm conditions even without the transport of hot air from other locations. Should such a hot air mass travel above a large body of water, as a
sirocco of Saharan origin crossing the Mediterranean sea, it likely picks up much water vapor with a reduction in temperature but far greater
humidity that makes the original desert air little less moderate as demonstrated in a high
heat index. Heat waves can also come from air originating over tropical seas penetrating far into the middle latitudes, as often occurs in the eastern United States and southeastern Canada. The
heat island effects of large cities only exacerbate heat in large cities that endure heat waves because of the weakness of night-time cooling.
Hyperthermia, also known as heat stroke, becomes commonplace during periods of sustained high temperature and humidity. Sweating is absent from 84%-100% of those affected. 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.
[8]
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 stocking and elevating the affected legs with 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
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.
Mortality
Heat waves are the most lethal type of weather phenomenon, overall. 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.
[9] The average annual number of fatalities directly attributed to heat in the United States is about 400.
[10] The
1995 Chicago heat wave, one of the worst in US history, led to approximately 600 heat-related deaths over a period of five days.
[11] 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.
[12] [13]
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." "Heat doesn't bother me much, but I worry about my neighbors," said one of his older respondents.
[14] 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.
[15]
; Underreporting and "Harvesting" effect
The number of heat fatalities is likely highly underreported due to 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 reduction in mortality suggests that heat affects especially those so ill that they "would have died in the short term anyway".
[16]
Psychological and sociological effects
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.
[17]
Power outage
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.
[18]
The heat wave in Melbourne, Australia also caused major power disruptions leaving over half a million people without power as the heat wave blew transformers and overloaded the power grid.
Wildfires
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 of
forest and of agricultural land and causing an estimated
€1 billion worth of damage.
[19] High end
farmlands have irrigation systems to back up
crops with.
Physical damage
Heat waves can and do cause roads, highways to buckle, water lines to burst, power transformers to detonate, causing fires. See the
2006 North American heat wave article about heat waves causing physical damage.
History
The record for the longest heat wave in the world is generally accepted to have been set at
Marble Bar in Australia, where from October 31, 1923 to April 7, 1924 the temperature broke the benchmark, setting the heat wave record at 160 days.
[20]
20th century
The heat waves of 1972 in New York and Northeastern United States were significant. Almost 900 people perished; the heat conditions lasted almost 16 days.
During another heat wave in the summer of 1983 temperatures over 100 degrees F were common across
Iowa,
Missouri,
Illinois,
Michigan,
Wisconsin,
Indiana,
Ohio,
Minnesota,
Nebraska and certain parts of
Kentucky.(and to this day the summer of 1983 remains on record as one of the hottest summers ever recorded in many of the states affected.) The hundred-degree readings were accompanied by very dry conditions connected by drought affecting the
Corn Belt States and
Upper Midwest. The heat also affected
Georgia and
New York City that same summer. New York Times represented articles about the heat waves of 1983, affecting the
central United States.
[21]
right
During 1988 intense heat spells in combination with the
drought of 1988 caused deadly results across the United States. Some 5,000 to 10,000 people perished because of constant heat across the United States although-according to many estimates-total death reports run as high as next to 17,000 deaths.
[22]
The heat waves of 1999 dominated states in the northeastern United States and other areas. Between 500 and 700 were killed because of blistering spells of scorching heat all over the United States.
21st century
The
European heat wave of 2003 killed around 35,000 people. Much of the heat was concentrated in France, where nearly 15,000 people died . In Portugal, the temperatures reached as high as 48 °C (118 °F) in the south.
The
European heat wave of 2006 was the second massive heat wave to hit the continent in four years, with temperatures rising to in
Paris; in
Ireland, which has a moderate maritime climate, temperatures of over were reported. Temperatures of were reached in the
Benelux and
Germany (in some areas , while
Great Britain recorded . Many heat records were broken (including the hottest ever July temperature in
Great Britain) and many people who experienced the heat waves of 1976 and 2003 drew comparisons with them.
In July 2006, the United States experienced a
massive heat wave, and almost all parts of the country had recorded temperatures above the average temperature for that time of year. Temperatures in some parts of South Dakota exceeded , causing many problems for the residents. Also, California experienced temperatures that were extraordinarily high, with records ranging from 100 to 130 °F (38 to 54 °C). On July 22, the
County of Los Angeles recorded its highest temperature ever at .
[23]
The
European heat wave of 2007 affected primarily south-eastern Europe during late June through August. Bulgaria experienced its
hottest year on record, with previously unrecorded temperatures above . The
2007 Greek forest fires were associated with the heat wave.
During the
2007 Asian heat wave, the Indian city of
Datia experienced temperatures of .
In January 2008,
Alice Springs in Australia's
Northern Territory recorded ten consecutive days of temperatures above with the average temperature for that month being . In March 2008, Adelaide,
South Australia experienced maximum temperatures of above for fifteen consecutive days, seven days more than the previous longest stretch of days. The March 2008 heat wave also included eleven consecutive days above .
[24] The heat wave was especially notable because it occurred in March, an autumn month, in which Adelaide averages only 2.3 days above .
[25]
The eastern United States experienced an early Summer heat wave during June 6-10, 2008 with record temperatures.
[26] There was a heat wave in Southern California beginning late June,
[27] which contributed to widespread fires. On July 6, a renewed heat wave was forecast, which was expected to affect the entire state.
[28] [29]
In early 2009,
Adelaide,
South Australia was hit by a
heat wave with temperatures reaching 40+ °C for six days in a row, while many rural areas experienced temperatures hovering around about mid 40s °C (mid 110s°F). Kyancutta on the Eyre Peninsula endured at least one day at 48°C, with 46 and 47 being common in the hottest parts of the state.
Melbourne, in neighbouring
Victoria recorded 3 consecutive days over , and also recorded its highest ever temperature 8 days later in a secondary heatwave, with the mercury peaking at . During this heat wave Victoria suffered from
large bushfires which claimed the lives of more than 210 people and destroyed more than 2,500 homes. There were also over half a million people without power as the heatwave blew transformers and the power grid was overloaded.
In August 2009,
Argentina experienced a period of unusual and exceptionally hot weather during August 24-30,
2009 during the Southern Hemisphere winter, just a month before Spring
[30] when a unusual and unrecorded
winter heat wave hit the the country. A shot of
tropical heat drawn unusually far southward hiked temperatures 22 degrees above normal in the city of
Buenos Aires and across the northern-centre regions of the country. Several records were broken.
Even though normal high temperatures for late
August are in the lower , readings topped degrees at midweek, then topped out above degrees during the weekend.
[31]
Temperatures hit on 29 August and finally on 30 August in Buenos Aires, making it the hottest day ever recorded in winter breaking the
1996 winter record of . In the city of
Santa Fe, a remarkable degrees on 30 August was registered, notwithstanding the normal high in the upper 15°C/60°Fs.
As per the
Meteorological Office of Argentina August 2009 has been the warmest month during winter since official measurements began
[32].
See also
- Cold wave
- Heat burst
- List of severe weather phenomena
- Urban heat island
Notes
- More Intense, More Frequent, and Longer Lasting Heat Waves in the 21st Century
- On the Definition of a Heat Wave
- Observed coherent changes in climatic extremes during the second half of the twentieth century
- Glossary of Meteorology
- http://www.weather.gov/glossary/index.php?word=heat+wave
- Canicule - definitionfo
- More heatwaves to come, Australians warned
- Extreme Heat
- Hot Weather Tips and the Chicago Heat Plan
- Relation between Elevated Ambient Temperature and Mortality: A Review of the Epidemiologic Evidence
- ''Near-Fatal Heat Stroke during the 1995 Heat Wave in Chicago''. ''Annals of Internal Medicine'' Vol. 129 Issue 3
- Heat Wave: A Social Autopsy of Disaster in Chicago
- ''Dead Heat: Why don't Americans sweat over heat-wave deaths?'' By Eric Klinenberg. Slate.com. Posted Tuesday, July 30, 2002
- ''Floods, Tornadoes, Hurricanes, Wildfires, Earthquakes... Why We Don't Prepare'' By Amanda Ripley. Time. August 28, 2006.
- Most People Struck Down by Summer Heat Are Poor Newswise, Retrieved on July 9, 2008.
- The Impact of Heat Waves and Cold Spells on Mortality Rates in the Dutch Population
- Thermal stress in the U.S.A.: effects on violence and on employee behaviour
- Heat Eases, but Thousands of Southern Californians Still Lack Power
- Climate Impacts
- Australian Climate Extremes: Marble Bar heatwave, 1923-24
- St. Louis Bears Brunt of Heat Wave as U.S. Toll Rises
- Billion Dollar U.S. Weather Disasters
- In Woodland Hills, It's Just Too Darn Hot
- Adelaide, South Australia March 2008 Daily Weather Observations
- Climate statistics for Australian locations
- [1], [1].
- Heat wave continues to blister SoCal, USA Today, June 19, 2008.
- Heat wave coming to scorched California, UPI.com
- Bay Area Braces For 'Scorchers' As Temps Rise, cbs5.com, July 7th, 2008.
- La temperatura llego a 34.7° y ya es un record/Clarin.com
- StarTribune
- Situacion extrema climatica en Argentina durante Agosto 2009 (In Spanish)