Increasingly frequent heat waves: what they are and how they are generated



by LORENZO CIOTTI

Increasingly frequent heat waves: what they are and how they are generated

A heat wave is a period of atmospheric weather during which the temperature is unusually high compared to the average temperatures usually experienced in a given region, in that period and with persistent characteristics.

It should not be confused with the more specific heat bubble phenomenon. The Royal Netherlands Meteorological Institute defines a heat wave as a period of at least 5 days with a maximum temperature above 25°C, of which at least 3 days with a temperature above 30°C.

Often, but not always, heat waves are associated with sultriness. According to scientists, heat waves have become more frequent and intense in recent years due to the current global warming, they would be one of the ways in which this warming would manifest itself at a meteorological level, ie in the short term.

Often, but not always, the most intense heat waves are preceded by another mini heat wave, lasting a few days, which acts as an anticipation of the second one. Like severe cold waves, severe heat waves pose a health risk, especially for the elderly and children and people suffering from chronic diseases In Europe these summer heatwaves are generally linked to the latitudinal shifts of the African subtropical anticyclone which normally station at subtropical latitudes, while in other areas of the world it is always the subtropical anticyclones that determine the heatwaves with their shifts.

Increasingly frequent heat waves: what they are and how they are generated

In the Eastern United States a heat wave can occur when a high pressure system originating in the Gulf of Mexico becomes stationary just off the Atlantic Seaboard.

Warm humid air masses form over the Gulf of Mexico and the Caribbean Sea while warm dry air masses form over the desert Southwest and northern Mexico. The SW winds on the back side of the High continue to pump hot, humid Gulf air northeastward resulting in a spell of warm and humid weather for much of the Eastern States.

In the Western Cape Province of South Africa, a heat wave can occur when a low pressure offshore and high pressure inland air combine to form a Bergwind. The air warms as it descends from the Karoo interior, and the temperature will rise about 10°C from the interior to the coast.

Humidities are usually very low, and the temperatures can be over 40 °C in summer. The highest official temperatures recorded in South Africa (51.5 °C) was recorded one summer during a bergwind occurring along the Eastern Cape coastline.

More than 70,000 Europeans died as a result of the 2003 European heat wave. Mortality due to heat waves could be reduced if buildings were better designed to modify the internal climate, or if the occupants were better educated about the issues, so they can take action on time.

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