Extreme Temperature

Changes in temperature extremes tend to follow mean temperature changes in many parts of the world. IPCC indicate that cold extreme cold extremes warm faster than warm extremes by about 30% – 40% globally averaged (Andreas Strerl et al, 2008). Many areas of society are susceptible to the effects of extreme temperatures. Unusually high summer temperatures raise power demand for air conditioning, increase heat stress on crops, and may create dangerous conditions for human health. Low winter temperatures may cause damaging frosts and freezes, increase heating demands, and may disrupt transportation (Henderson et al, 1997).

Although they happen more slowly and are more difficult to see than a tornado or an earthquake, "heat waves" and "cold snaps" are deadly natural hazards. Extreme heat and cold occur somewhere in the world every year and can afflict nearly every location on Earth. Heat waves are periods of unusually high temperatures, usually lasting three days to three weeks. Typically, heat waves are characterized by temperatures of 35°C (95°F) or higher, although lower temperatures accompanied by high humidity levels can also be considered a heat wave. Cold snaps are commonly three days to three weeks in duration, with temperatures usually falling below -15°C (5°F).

Temperature extremes are most common in the mid-latitude regions, especially near the interior of large continents, such as North America. Here, without the moderating effects of the oceans, winter minimum temperatures can drop below -20°C (-4°F) and above 40°C (104°F) for several weeks. In the mid-latitude regions, temperature extremes are most common June through August, and December through February. In Polar Regions and the higher mid-latitudes, extreme low temperatures can occur anytime between late fall and early spring. In the lower mid-latitudes, extreme high temperatures are common from late spring through early fall. Much like high latitudes, high altitudes are frequently subject to extreme low temperatures. In alpine areas, which are typically above 3500 m (11,500 ft) depending on latitude, extreme low temperatures can occur for nine months or more during a year[1].


1.    Heat Wave

Heat wave or extreme heat is the temperatures that hover 10 degrees or more above the average high temperature for the region and last for several weeks are defined as extreme heat. Humid or muggy conditions, which add to the discomfort of high temperatures, occur when a "dome" of high atmospheric pressure traps hazy, damp air near the ground. Excessively dry and hot conditions can provoke dust storms and low visibility. Droughts occur when a long period passes without substantial rainfall. A heat wave combined with a drought is a very dangerous situation[2].

Source: WMO

A basic definition of a heat wave implies that it is an extended period of unusually high atmosphere-related heat stress, which causes temporary modifications in lifestyle and which may have adverse health consequences for the affected population. Thus, although a heat wave is a meteorological event, it cannot be assessed without reference to human impacts[3].



People living in urban areas may be at greater risk from the effects of a prolonged heat wave than people living in rural regions[4]. Heat wave impacts are widespread. While a large number of deaths may not occur in a single city every year, the cumulative impacts across broad regions over several days to weeks can result in heavy loss of life. Many more hundreds of deaths are associated with excessive heat attributed to heart attack, stroke, and also respiratory stress. Most deaths occur in urban areas where concrete, asphalt, and physical structures raise temperatures in urban heat islands, and nighttime temperatures remain above average. Heat waves also impact farming and ranching through loss of cattle and other livestock. Below are several impacts caused by heat waves[5]:

  1. Illnesses caused by exposure to high temperatures include heat cramps, fainting, heat exhaustion, heatstroke, and death.
  2. Population at increased risk especially older and younger people, risk of dehydration, low fitness/excessive exertion, etc.
  3. Another reason of death during heat wave is because of living alone. Studies designed to investigate why some people died during the 1995 and 1999 heat waves in Chicago found that the strongest risk factor was living alone, particularly for those who did not leave home daily.

Learn also about the impacts of the heat wave during the summer 2003 in Europe and the social impacts of heat waves in England.


Emergency Action

What you should do if the weather is extremely hot[6]:

  • Stay indoors as much as possible and limit exposure to the sun.

  • Stay on the lowest floor out of the sunshine if air conditioning is not available.

  • Consider spending the warmest part of the day in public buildings such as libraries, schools, movie theaters, shopping malls, and other community facilities. Circulating air can cool the body by increasing the perspiration rate of evaporation.

  • Eat well-balanced, light, and regular meals. Avoid using salt tablets unless directed to do so by a physician.

  • Drink plenty of water. Persons who have epilepsy or heart, kidney, or liver disease; are on fluid-restricted diets; or have a problem with fluid retention should consult a doctor before increasing liquid intake.

  • Limit intake of alcoholic beverages.

  • Dress in loose-fitting, lightweight, and light-colored clothes that cover as much skin as possible.

  • Protect face and head by wearing a wide-brimmed hat.

  • Check on family, friends, and neighbors who do not have air conditioning and who spend much of their time alone.

  • Never leave children or pets alone in closed vehicles.

  • Avoid strenuous work during the warmest part of the day. Use a buddy system when working in extreme heat, and take frequent breaks.

Learn also the emergency response on extreme heat in CDC (Centers for Disease Control and Prevention) or learn through community response.



Learn about heat wave mitigation using GIS and an action from National Disaster Education Coalition (NDEC).


2.    Cold Wave

A cold wave is a weather phenomenon that is distinguished by marked cooling of the air, or the invasion of very cold air, over a large area. It can also be prolonged period of excessively cold weather, which may be accompanied by high winds that cause excessive wind chills, leading to weather that seems even colder than it is. Cold waves can be preceded or accompanied by significant winter weather events, such as blizzards or ice storms. Other names of a cold wave include cold snap and deep freeze[7].



Some impacts of cold wave[8]:

  • Sudden cold waves can have detrimental effects on human beings. A cold wave that is unexpected can cause frost bites, hypothermia or other serious medical aliments.

  • A lot of damage is caused to animals and wildlife. When a cold wave comes along with heavy and incessant snowfall, animals may not be able to graze and thus die out of starvation. In order to feed livestock, farmers have to pay high prices for buying their food.

  • There can be cases of damage when water pipelines freeze and burst.

  • There is a rise in the demand for fuels and electricity.

See also the effects of cold wave on agricultural in India from 2002-2003 and also news about the effects of cold wave in Peru.


Emergency Action

Emergency response guidelines on cold wave[9]:

  • Stay indoors as much as possible.

  • Listen to the radio or television for weather reports and emergency information.

  • Conserve fuel, if necessary, by temporarily closing off heat to some rooms.

  • Eat to supply heat to the body and drink non-alcoholic beverages to avoid dehydration.

  • Wear several layers of loose fitting, lightweight; warm clothing rather than one layer of heavy clothing. The outer garments should be tightly woven and water repellent.

  • Carry a "basic vehicle emergency kit" in the trunk of your vehicle.



Extreme temperatures cannot be forecasted on a long-term basis and cannot be directly mitigated. They can however be managed by proper disaster plans that regulate authorities and emergency facilities in case of a heat or cold wave[10].

International weather forecasts are the main source of information. For this purpose, consult for example:

  • WMO's World Weather Information Service: http://www.worldweather.org/

  • WMO's Severe Weather Information Centre also provides forecasts on severe weather events, which are likely to occur worldwide. http://severe.worldweather.org/

Regional and National weather service give more precise forecasts and weather information. Below are some examples:

  • Europe Meteoalarm http://www.meteoalarm.eu/

  • Regional forecasts from the WMO http://www.worldweather.org/asia.htm

  • Links to national weather services provided by the WMO: http://www.wmo.int/pages/members/index_en.html

  • South African weather service: http://www.weathersa.co.za/Menus/WXandClimate.jsp

  • United States, NOAA (National oceanic and atmospheric administration): http://www.noaa.gov/wx.html

  • etc