Last week, Europe went through a heatwave that lasted six days, smashed temperature records, left two people dead in France and another two in Spain, and caused huge fires to break out, including one that spanned 10,000 acres in France.

Why it is happening
The heatwave in Europe is a result of warm air masses from Africa, the World Meteorological Organization (WMO) said. The heatwave in Europe follows extreme heat episodes in India, Pakistan, parts of the Middle East and Australia. More events are expected to follow during this northern hemisphere summer, the WMO said.

Some scientists have blamed climate change for heatwaves. Apart from heatwaves, various climate models have predicted alternating periods of prolonged droughts and heavy flooding in some areas.

What is a heatwave
Classifying a heatwave varies from country to country, because what is seen as extremely hot in one place may seem within normal range in another. In guidelines published in 2016, the WMO listed several factors to be considered while analysing an extreme weather event such as a heatwave.

Definition in India
The India Meteorological Department does not consider a heatwave unless the maximum temperature crosses 40°C in the plains and 30°C in the hills. Where the normal maximum is 40°C or less, the heatwave departure from normal is 5°C to 6°C and the severe heatwave departure is 7°C or more. Where the normal maximum is more than 40°C, the heatwave departure from normal is 4°C to 5°C while the severe heatwave departure is 6°C or more. In places where the maximum temperature reaches 45°C or more, the IMD declares a heatwave irrespective of the normal.