Woman sitting in a fountain under a waterfall during a heat wave

What is a heat wave?

A heat wave occurs when the daily maximum temperature exceeds the average maximum temperature by 9 degrees for more than five consecutive days. It is usually a period of abnormal, uncomfortable, hot and humid weather.

What are the origins of a heat wave?

These waves are caused by very warm and stagnant air masses. Regions experiencing intense heat waves are usually dominated by a surface high pressure system with a mid-tropospheric ridge aloft. Dew points are also high and, to complicate matters, wind speeds are often low.

Clear or partly cloudy skies allow the intense solar energy to heat the ground and the air mass more. High humidity and stagnant air reduce the body's ability to cool itself through perspiration. Lives are at risk when these conditions persist day and night for several days, especially if there is no possibility of to refresh oneself.

What are the consequences of a heat wave?

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A prolonged heatwave can lead to widespread use of air conditioning, resulting in increased demand for electricity, which puts a strain on gas and electricity companies. Transport can be hampered when roads and railways buckle in the heat.

All types of outdoor work, such as landscaping and construction, experience reduced productivity. Agriculture is particularly vulnerable, as heat waves destroy crops and kill livestock.