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A scientific name for sudden temperature increase events is suggested

Vertical cross section of the simulated air temperature and humidity at 3 p.m. on 27 August 2010 (Collserola on the left and the sea on the right).

Vertical cross section of the simulated air temperature and humidity at 3 p.m. on 27 August 2010 (Collserola on the left and the sea on the right).


In a paper published on the journal Natural Hazards and Earth System Sciences, researchers Jordi Mazon and David Pino, from Castelldefels School of Telecomunications and Aerospace Engineering (EETAC) of the Universitat Politècnica de Catalunya • BarcelonaTech (UPC), and Mariano Barriendos, from the University of Barcelona (UB), suggest to name sudden temperature increase events that last less than two consecutive days as flash heats. Nowadays, there is not any scientific name to refer to these abnormal high temperature events, although the phenomenon has been identified in several occasions. The new name may bring changes in response protocols to prevent heat illness and forest fires, as well as in insurance cover against the damage caused by these phenomena.

On one hand, the World Meteorological Organization defines a heat wave as a phenomenon in which the daily maximum temperature of at least two consecutive days exceeds the average maximum temperature by 5 °C. On the other hand, the American Meteorological Society defines a heat burst as a similar event that usually takes place during a few minutes, and up to one or two hours exceptionally.

Therefore, international organizations identify microscale (heat bursts) and macroscale (heat waves) phenomena, but they do not recognize the ones that belong to the mesoscale. In this context, researchers identify a type of temperature increase event that remains little studied, even if it can have impacts on several fields: health, agriculture, climate change research or electricity consumption. Jordi Mazon, David Pino and Mariano Barriendos suggest naming this type of event flash heats, as they cannot be considered heat waves, nor heat bursts.


Maximum daily temperature recorded in Barcelona

The research is based on surface observations and numerical simulation considering the temperature and humidity data collected in Barcelona on 27 August 2010 and in Heraklion (Crete, Greece) on 21 March 2008. In Barcelona, the temperature reached 39.8 °C, which is the maximum temperature value recorded during 230 years of daily data series. The period of abnormally high temperatures lasted less than 10 hours. The event was described as a small heat wave because we lack a specific name for this phenomenon.

In the case of Greece, an event of abnormal temperature increase that lasted 12 hours was identified in 2008; on 21 March morning, the recorded temperature reached 34 °C. Both events showed a rapid temperature increase by at least 5 °C the average and were caused by the rapid movement of a ridge from North Africa accompanied by a warm air mass. A ridge is a line of relatively high pressure forming an arm out of a defined high, but not forming a closed loop. The ridge from North Africa brings warm air to the Iberian Peninsula and, consequently, temperature is increased.

Besides ridge movements, flash heats are also caused by a persistent and strong Foehn effect. It is a type of dry, warm, down-slope wind that occurs in the lee of a mountain range. It is a rain shadow wind that results from the subsequent adiabatic warming of air that has dropped most of its moisture on windward slopes. Both, ridges and the Foehn effect, mean an increase in temperature that does not last more than 48 hours, so it cannot be considered a heat wave.

Effects on the study of climate change

To differentiate between heat wave and flash heat may help to study more precisely atmospheric behaviour, global warming dynamics and evolution and, thus, to go more deeply into climate change research.

Furthermore, authors analyse possible impacts on agriculture, energy consumption, environment and health. Concerning environment and health, flash heats are likely to be one of the main risks in triggering wild fires and causing heat illness. However, if abnormally high temperature events do not last for more than two consecutive days, they are not considered a heat wave, so fire response protocols are not activated and people do not receive information about how to prevent a heat illness.

Flash heats may also have some effects on energy consumption or cause crop damage. These effects could be prevented if events are identified and better studied. Moreover, the damage caused by them is not usually covered by the insurance because the policy does not include flash heats as they are not recognised by organizations concerned. In most cases, insurance only covers those events identified as heat waves.

After having published the study on the journal Natural Hazards and Earth System Sciences in February, researchers will propose the new term and its definition to the World Meteorological Organization by means of the Meteorological Service of Catalonia and the Agency of Spanish Meteorology.
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