A heat wave is a prolonged period of excessively hot
weather, which may be accompanied by high humidity. There is no universal definition of a heat wave;cite journal |last=Meehl |first=George A. |coauthors=Tebaldi, Claudia |title=More Intense, More Frequent, and Longer Lasting Heat Waves in the 21st Century |journal=Science |date= 2004-08-13|volume=305 |issue=5686 |url=http://www.sciencemag.org/cgi/content/full/305/5686/994 |pmid=15310900 |doi=10.1126/science.1098704 |pages=994 ] 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 climatepattern for that area. [cite journal |last=Robinson |first=Peter J. |title=On the Definition of a Heat Wave |journal= Journal of Applied Meteorology|month=April | volume=40 |issue=4 |pages=762–775 |publisher= American Meteorological Society|url=http://ams.allenpress.com/amsonline/?request=get-abstract&doi=10.1175%2F1520-0450(2001)040%3C0762:OTDOAH%3E2.0.CO%3B2 |year=2001 |doi=10.1175/1520-0450(2001)040<0762:OTDOAH>2.0.CO;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.
anomalies, March to May, 2007] The definition recommended by the World Meteorological Organizationis 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. [cite journal |last=Frich |first= A.|coauthors=L.V. Alexander, P. Della-Marta, B. Gleason, M. Haylock, A.M.G. Klein Tank, and T. Peterson |year=2002 |month=January |title=Observed coherent changes in climatic extremes during the second half of the twentieth century |journal=Climate Research |volume= 19 |pages=193–212 |url=http://cccma.seos.uvic.ca/ETCCDMI/docs/Frichetal02.pdf |doi=10.3354/cr019193|format=PDF]
A formal, peer-reviewed definition from the "Glossary of Meteorology" is:<cite book |last=Glickman |first=Todd S. |title=Glossary of Meteorology |publisher=
American Meteorological Society|month=June | year=2000 |location=Boston |url=http://amsglossary.allenpress.com/glossary ] : 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 convert|90|°F|°C|abbr=on. More realistically, the comfort criteria for any one region are dependent upon the normal conditions of that region.
heat stormis an extended heat wave. Heat storms occur when the temperature reaches 100 °F (38 °C) for three or more consecutive days over a wide area (tens of thousands of square miles).
Netherlands, a heat wave is defined as period of at least 5 consecutive days in which the maximum temperature in De Biltexceeds 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). [http://www.knmi.nl/VinkCMS/explained_subject_detail.jsp?id=3777] . This definition of a heat wave is also used in Belgiumand Luxembourg.
Denmarka 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.
United States, definitions also vary by region; however, a heat wave is usually defined as a period of at least three consecutive days above 90 °F (32.2 °C). [http://www.weather.gov/glossary/index.php?word=heat+wave] The National Weather Servicecriterion for the issuance of a heat advisoryis when the heat indexis expected to (or does) reach 105 °F (40.6 °C) with a nighttime low temperature not below 80 °F (26.7 °C), whereas an excessive heat warningis issued when a maximum heat index exceeding 115 °F (46.1 °C) with minimum 80 °F (26.7 °C) is expected (or is occurring).
Heat waves often occur during the
Dog Daysof 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." [cite web |title=Canicule - definitionfō |work=About.com |url=http://frenchfood.about.com/library/blcanicule.htm |accessdate=2006-07-27]
Some regions of the globe are more susceptible to heat waves than others, such as Mediterranean-type climates with a summer dry spell which becomes much hotter than usual during certain years.Fact|date=February 2007
How they occur
In the summer in warm climates, if there is an area of high pressure with little or no rain and clouds, there is nothing to protect the air and ground from being heated excessively. When large high pressure air is trapped, the ground and air will continue to heat and the heat wave will last longer.
The position of the
jet streamis very important because the air on one side is hot while the other side is cold. Heat waves are far more likely and more severe when you are on the hot side. Sometimes the jet stream does not move far enough to make many areas that normally get hot on the hot side; but sometimes many cold areas are made hot abnormally.The effects of El Niño and La Niña (opposite reaction to El Niño) can severely disrupt the positions of the jet streams.
Large desert zones and dry areas are more likely to get extreme heat because there is rarely any high cloud cover with very low humidity, making it like a furnace.
The direction of the wind is a very important part of the reasons for heat waves, because this pushes hot air towards colder areas if they are going away from the deserts and equator.The higher the force of the wind as well as the distance they travel from the hotter to colder areas, generally means hotter weather.
Cities also get hotter because they generate heat from the use of power, usually by about 1-2 °C or so and experience very warm night time minimum temperatures putting further strain on energy demands.
Humidityalso has a serious effect on how hot it feels but this does not make the actual temperatureany hotter. Heat Waves in Eastern North Americaand North Western Europeare usually accompanied by high humidity, aggravating the heat index (one's discomfort), as opposed to the drier heat typically experienced during heat waves in continental Europe, Western North Americaor cities in Australia.
Perhaps the most well-known heat-related illness is
hyperthermia, also known as heat stroke. Classic heat stroke occurs 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.cite web |title=Extreme Heat |work=FEMA:Are You Ready? |url=http://www.fema.gov/areyouready/heat.shtm |accessdate=2006-07-27 ]
edemapresents 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 rashaccompanied by acute inflammationand 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 dermatitisor 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 lotionto remove any desquamated skin. The associated itching may be treated with topical or systemic antihistamines. If infection occurs a regimen of antibiotics is required.
1936 North American heat wave. Record temperatures were based on 112 year records] Heat crampsare 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 hyponatremiathat induces cramping in stressed muscles. Rehydrationwith salt-containing fluids provides rapid relief. Patients with mild cramps can be given oral .2% salt solutions, while those with severe cramps require IV isotonicfluids. The many sport drinks on the market are a good source of electrolytes and are readily accessible. Heat syncopeis 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
last = Klinenberg
first = Eric
title = Heat Wave: A Social Autopsy of Disaster in Chicago
url = http://www.press.uchicago.edu/Misc/Chicago/443213in.html
year = 2002
publisher = Chicago University Press
location = Chicago, IL ] " [http://slate.com/id/2068612/ Dead Heat: Why don't Americans sweat over heat-wave deaths?] " By Eric Klinenberg. Slate.com. Posted Tuesday, July 30, 2002] 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." [http://www.time.com/time/magazine/article/0,9171,1229102,00.html Floods, Tornadoes, Hurricanes, Wildfires, Earthquakes... Why We Don't Prepare] " By Amanda Ripley. Time. August 28, 2006.] According to the Agency for Healthcare 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. [ [http://newswise.com/articles/view/542519/ Most People Struck Down by Summer Heat Are Poor] Newswise, Retrieved on July 9, 2008.]
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".cite journal |last=Huynen |first=Maud M.T.E. |coauthors=Pim Martens, Dieneke Schram, Matty P. Weijenberg, and Anton E. Kunst |title =The Impact of Heat Waves and Cold Spells on Mortality Rates in the Dutch Population |journal=
Environmental Health Perspectives|volume=109 |issue=5 |pages=463–470 |publisher= National Institute of Environmental Health Sciences|month=May | year=2001 |url=http://www.ehponline.org/docs/2001/109p463-470huynen/abstract.html |doi =10.2307/3454704 ]
Psychological and sociological effects
In addition to physical stress, excessive heat causes psychological stress, to a degree which affects employee performance, and is also associated with an increase in violent crime.cite journal |last=Simister |first=John |coauthors=Cary Cooper |title=Thermal stress in the U.S.A.: effects on violence and on employee behaviour |journal=
Stress and Health|volume=21 |issue=1 |pages=3–15 |publisher= International Society for the Investigation of Stress|month=October | year=2004 |url=http://www3.interscience.wiley.com/cgi-bin/abstract/109716549/ABSTRACT?CRETRY=1&SRETRY=0 |doi=10.1002/smi.1029 ]
Heat waves often lead to
electricityspikes due to increased air conditioninguse, 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. [cite news |last=Doan |first=Lynn |coauthors=Covarrubias, Amanda |title=Heat Eases, but Thousands of Southern Californians Still Lack Power |publisher= Los Angeles Times|date= 2006-07-27|url=http://www.latimes.com/news/local/la-me-heat27jul27,1,4111447.story |accessdate=2008-07-28 ]
If a heat wave occurs during a
drought, which dries out vegetation, it can contribute to wildfires. During the disastrous heat wave that struck Europe in 2003, fires raged through Portugal, destroying over 3010 km² (740,000 acres) of forestand 440 km² (108,000 acres) of agricultural land and causing an estimated €1 billion worth of damage. [cite news |last=Bell |first=M. |coauthors=A. Giannini, E. Grover, M. Hopp, B. Lyon, A. Seth |title=Climate Impacts |work=IRI Climate Digest |publisher= The Earth Institute|date=September 2003 |url=http://iri.columbia.edu/climate/cid/Sep2003/impacts.html |accessdate=2006-07-28 ] High end farmlands have irrigation systems to back up crops with.
Heatwaves can and do cause roads, highways to buckle, water lines to burst, power transformers to detonate, causing fires. See the
2006 North American heat wavearticle about heatwaves causing physical damage.
During 1988 extremely intense
heat spellsaccompanied by the Drought of 1988caused deadly results across the United States. Almost 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 17000 deaths. [cite web |title=Billion Dollar U.S. Weather Disasters |publisher=National Climatic Data Center |url=http://lwf.ncdc.noaa.gov/oa/reports/billionz.html |accessdate=2008-07-14]
During 1983 temperatures over 100 degrees were common across
Iowa, Missouri, Illinois, portions of Wisconsin, Indianaand even Nebraska. The hundred-degree readings were accompanied by very dry conditions connected by drought affecting the Corn Belt Statesand Upper Midwest. The death toll was catastrophic and highly staggering. New York Times represented articles about the Heat Spell of 1983affecting the Central United StatesRegion.
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 Fact|date=March 2008.
Heat Waves of 1972in New York decimated the area and stole many lives. Ninety degree temperatures-and in some cases one hundred and greater-affected the Northeastern United Statesin 1972. Almost 900 people perished, the heat conditions lasted almost 16 days.
European heat wave of 2006was the second massive heat wave to hit the continent in 4 years, with temperatures rising to 40 °C (104 °F) in Parisand even Ireland, which has a moderate maritime climate, reporting temperatures of over 32C (90 °F). Temperatures of 35 °C (95 °F) were reached in the Beneluxand Germany, while the United Kingdomrecorded convert|37|°C|°F|abbr=on. Many heat records were broken (including the hottest ever July temperature in the UK) and many people who experienced the heat waves of 1976 and 2003 drew comparisons with them. The Heat Waves of 1999dominated states in the Northeast United Statesand other areas. Between 500-700 were killed because of blistering spells of scorching heat all over the United States.
In early 2006,
Adelaide, South Australiawas hit by a dry heat wave with temperatures reaching 40+ °C for five days in a row, while Port Augustaexperienced temperatures hovering around about mid 40s °C (mid 110s°F) with one day recorded at approx convert|48|°C|°F|abbr=on. Also in Sydneyit reached convert|44.2|°C|°F|abbr=on on the first day of 2006 [cite web | title = 3rd warmest summer on record for Sydney | publisher = Bureau of Meteorology| date = 2006-03-01| url = http://www.bom.gov.au/announcements/media_releases/nsw/20060301.shtml | accessdate = 2008-04-24 ] .
2007 European heat waveaffected primarily Southeastern Europe during late June through August. Bulgaria experienced its hottest year on record, with previously unrecorded temperatures above convert|45|°C|°F|abbr=on. The 2007 Greek forest fireswere associated with the heatwave.
2007 Asian heat wave, the Indian city of Datiaexperienced temperatures of convert|48|°C|°F|abbr=on.
In January 2008,
Alice Springsin Australia's Northern Territoryrecorded ten consecutive days of temperatures above convert|40|°C|°F|abbr=on with the average temperature for that month being convert|39.8|°C|°F|abbr=on. In March 2008, Adelaide, South Australiaexperienced maximum temperatures of above convert|35|°C|°F|abbr=on for fifteen consecutive days, seven days more than the previous longest stretch of convert|35|°C|°F|abbr=on days. The March 2008 heat wave also included eleven consecutive days above convert|38|°C|°F|abbr=on [cite web | title = Adelaide, South Australia March 2008 Daily Weather Observations | publisher = Bureau of Meteorology| date = 2008-04-21| url = http://www.bom.gov.au/climate/dwo/200803/html/IDCJDW5002.200803.shtml | accessdate = 2008-04-24 ] . The heat wave was especially notable because it occurred in March, an autumn month, in which Adelaide averages only 2.3 days above convert|35|°C|°F|abbr=on [cite web | title = Climate statistics for Australian locations | publisher = Bureau of Meteorology| date = 2008-04-23| url = http://www.bom.gov.au/climate/averages/tables/cw_023090_All.shtml | accessdate = 2008-04-24 ] .
Eastern United States experienced an early Summer heatwave during June 6-10, 2008 with record temperatures. [ [http://www.nytimes.com/2008/06/11/nyregion/11heat.html?_r=1&fta=y&oref=slogin] , [http://nws.met.psu.edu/severe/2008/09Jun2008.pdf] .] There was a heat wave in Southern California beginning late June [ [http://www.usatoday.com/weather/news/2008-06-19-socal-heat-wave_N.htm Heat wave continues to blister SoCal] , USA Today, June 19, 2008.] , which contributed to wide-spread fires. On July 6th, a renewed heatwave was forecast, which was expected to affect the entire state. [ [http://www.upi.com/Top_News/2008/07/06/Heat_wave_coming_to_scorched_California/UPI-13351215345710/ Heat wave coming to scorched California] , UPI.com] [ [http://cbs5.com/local/bay.area.heat.2.765444.html Bay Area Braces For 'Scorchers' As Temps Rise] , cbs5.com, July 7th, 2008.]
During July 2008, Japan has suffered from a severe heat wave. [ [http://mdn.mainichi.jp/national/news/20080722p2a00m0na004000c.html Japan sizzles under heat wave] , Mainnichi News, July 22, 2008.]
The record for the longest heatwave in the world is generally accepted to have been set at
Marble Barin Australia, where from October 31, 1923 to April 07, 1924 the temperature broke the 37.8 °C/100 °F benchmark, setting the heat wave record at a scorching 160 days.
2008 Southern US Heat wave
* [http://www.fema.gov/areyouready/heat.shtm FEMA: Extreme Heat]
* [http://chicago.about.com/library/blank/bl_hot_weather_tips.htm Hot Weather Tips]
* [http://www.bom.gov.au/lam/climate/levelthree/c20thc/temp1.htm Marble Bar heatwave, 1923-1924]
* [http://www.vicasting.com/contents.aspx/pid/7119/ WeatherBug Weather Wrap]
* [http://www.ncdc.noaa.gov/oa/esb/?goal=climate&file=events/temp/ Social & Economic Costs of Temperature Extremes] from "NOAA Socioeconomics" website initiative
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