Heat Wave Definition
How do we define a heat wave? The Encyclopaedia Britannica defines it simply as ‘a period of exceptionally hot weather, often with high humidity’. But what is ‘exceptionally hot’? For the temporary residents of Casey in the Antarctic, the highest recorded temperature of 9.2°C must have felt like an exceptionally hot day. By contrast, the population of Marble Bar, a small town in Australia’s Pilbara region, may feel quite comfortable with their average daily maximum of above 40°C in summer. The town holds the infamous record of more than 170 consecutive days above 37.8°C. Despite these high temperatures, even the settlers of European descent think of it as nothing unusual – they are acclimatized.
Heat waves do have a much more dramatic effect on people living in a cool to mild climate. They experience a higher degree of stress to their bodies than acclimatized residents of subtropical and tropical regions do. For example, death rates in Great Britain and the Netherlands increase sharply when the thermometer climbs above 25°C.
Devastating heat waves in the last five years of the 20th century pose the question whether global warming has increased the frequency and severity of heat waves. There is no doubt that the earth is getting warmer. Highest ever temperatures are being recorded throughout the world. But many scientists are still not prepared to link these recent temperature extremes to global warming, as they say heat waves have been a fact of summer since recording started. To prove the trend of global warming, the climatologists require many more years of temperature records.
In the meantime, weather forecasting takes into account the impact of heat on human health. Weather services issue warnings whenever the temperature and humidity is expected to reach a certain level. Scientists developed an apparent temperature table: Heat Index. Community services issue emergency and educational messages through the media that deal with the health implications and prevention of heat-related illnesses. Employers agree to reduce the employee’s workload or stop work altogether on hot days.
Heat injures and kills, as we can see from the thousands of people who die of heat-related illnesses each year. In 1996, Pakistan and India experienced temperatures of up to 49°C in the shade; people died or were hospitalized for heatstroke, circulatory collapse or dehydration. The Indian press reported a death toll of 2500, but acknowledged that the number was probably much higher. The US experienced two particularly disastrous years: according to the Centres of Disease Control and Prevention, 1700 Americans died in 1980. The US National Weather Service reported 1021 deaths in 1995. In the UK and the Netherlands, temperatures above 25°C appear to have a close relationship with death rates for most diseases, excepting cancer.
Depending on the research methods, the figures that each government agency publishes often conflict. They have to rely heavily on death certificates and/or hospital reports issued by a medical officer. But how do these medical professionals classify a heat-related death?
A person died of a heart attack. Did the heart surrender to the demand of the body’s temperature control mechanism to pump large amounts of blood to the skin? Another person drank a considerable amount of alcohol during a hot day. Did the person die as a result of the toxic effect of alcohol, or due to a heatstroke? The heat most likely played a role in both cases. But would the person have lived under different circumstances? What was the primary cause?
These questions can lead to the speculation that the actual heat-related death toll is considerably under-reported. Critics suggest that the official figures should be up to twice as high but even as they currently stand, heat mortality rates are too high.
The media always seems to be preoccupied with death rates. We shouldn’t forget the many victims left with permanent health damage. A lack of records makes it hard to determine the number of people who become ill. But for every dead person there must be many more survivors burdened with brain, kidney or liver damage. Some will develop heat intolerance and will be in particular danger when the next heat wave comes around.
Urban Heat Island Effect
You sit on your shaded veranda and enjoy a cool drink. The sea breeze blows gently through the large open windows and coconut trees provide shade from the sun. Dream on: you are more likely one of the million city dwellers living in a brick or concrete bunker, built to save energy during frosty winter months. An environmentalist at heart, you installed small and double-glazed windows and insulated walls and ceiling. Good on you. To beat the summer heat, you rely on air conditioning – if you can afford it and if you have the electricity to run it. Open the windows? No way, burglars are in the streets. Anyway, the air outside is either hotter than inside or laden with pollutants.
Studies showed that the majority of heat wave fatalities occur in inner-city areas. The asphalt, brick and concrete jungle absorbs heat and retains it well into the night. On average, the inner city is 5 to 8°C hotter than the surrounding countryside – the heat island effect that NASA researched in 1998. Sensors in aircraft and satellites demonstrated that artificial surfaces reach temperatures 20°C-40°C higher than natural surfaces do – Salt Lake City rooftops, for instance, were 71°C. These figures also provide the answer: cities need more natural surfaces, especially trees, to cool down.
Unventilated apartment buildings and rooms without air conditioning can reach temperatures in excess of 50°C during heat wave conditions. Even if ventilation is possible, the temperature drops to just above the outside air temperature. Since hot air rises, the top levels of apartment buildings suffer most. Insulation will keep the heat out for a day or two. But eventually the room succumbs to the environment and the insulation becomes a curse.
Now that we are aware of the heat island effects, we can modify building codes and include simple requirements to protect buildings from the heat, e.g. the inclusion of more natural areas. These will not only modify the climate but save electricity as well. A homeowner should consider the effects of extreme heat on the home.
Simple measures to improve the climate of your home:
- Deciduous trees provide shade in the summer and let the sun’s radiation heat the house in winter.
- Orientate the house according to the elements. There is nothing worse than bedrooms facing the sun. Sleepless nights are virtually guaranteed.
- Include shaded verandas where possible.
- Light-coloured walls and roofs will reflect some of the sun’s radiation.
- The eaves should be wide enough to shade the windows in summer.