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; 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.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.
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.
A formal,
peer-reviewed definition from
the
Glossary of Meteorology is:
- 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).
Temperature anomalies, March to May,
2007
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. 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."
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.
Heat waves are spans of extreme heat.
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.
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.
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
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. 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 600
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." "Heat doesn't
bother me much, but I worry about my neighbors," said one of his
older respondents. 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.
- 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".
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.
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.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. High end
farmland
have irrigation systems to back up
crop 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.
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 andNew York City that same summer. New York Times represented
articles about the heat waves of 1983, affecting the
central United States.
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.
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.
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 .
- 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 .
The heat wave was especially notable because it occurred in March,
an autumn month, in which Adelaide averages only 2.3 days
above .
- The eastern United States experienced an early Summer heat wave
during June 6-10, 2008 with record temperatures. There was a heat
wave in Southern California beginning late June, which contributed
to widespread fires. On July 6, a renewed heat wave was forecast,
which was expected to affect the entire state.
- 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 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.
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.
See also
Notes
- http://www.weather.gov/glossary/index.php?word=heat+wave
- Near-Fatal Heat Stroke during the 1995 Heat Wave in
Chicago. Annals of Internal Medicine Vol. 129
Issue 3
- 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.
- [1], [2].
- 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)
External links