Why are countries around the world experiencing heatwaves?

People cooling themselves in the fountain outside the Louvre in Paris on July 19, 2022. PHOTO: EPA-EFE

The Straits Times looks at the reasons behind scorching temperatures around the world and their link to climate change.

What are heatwaves?

1. Warm air rises from the ground

2. High pressure cells in the atmosphere push warm air back towards the ground

3. The pressure traps hot air like a lid on a pot

4. Warm air compresses as it sinks, releasing more heat

5. Heat causes the ground to lose moisture and become even warmer, increasing the risk of wildfires

6. Fewer clouds are formed and this allows more sunlight to penetrate and warm the earth

Heatwaves around the world

Europe (England, Spain, Portugal, France)

A firefighter standing guard against a fire in the village of Tabara, near Zamora, north-west Spain, on July 18, 2022. PHOTO: AFP

How hot

In England, train tracks buckled, electricity companies reported mass outages and large grassland areas around London caught fire.

The authorities across southern Europe battled against huge wildfires in Spain, Greece and France on July 17, 2022. 

Hundreds of deaths were blamed on soaring temperatures.

Cause

The intense heat felt across Europe in the past few weeks is mainly due to the Azores High - a slow-moving semi-permanent high pressure cell, said Professor Matthias Roth from the Department of Geography at the National University of Singapore (NUS). 

Climate change has exacerbated the frequency of an extremely large Azores High, said National Institute of Education Assistant Professor Wang Jingyu.

What used to happen only once in 10 years in the pre-industrial period now occurs once every four years, said Prof Wang.

South Asia (India, Pakistan)

A girl selling water shielding herself from the sun in New Delhi on April 27, 2022. PHOTO: REUTERS

How hot

Record-shattering extreme temperatures were recorded between March and May, peaking at 50 deg C.

About 300 forest fires occurred in India in a single day on April 28, 2022.

Cause

As the climate warms, intense anti-cyclones are spawned more often, bringing heatwaves to India, said Singapore University of Social Sciences climate scientist Koh Tieh Yong.

Climate change reportedly made heatwaves in the region 30 times more likely.

Singapore

People walking in hot weather near Redhill MRT station on July 19, 2022. ST PHOTO: CHONG JUN LIANG

How hot

The last heatwave was in April 2016, the hottest year recorded, with an annual mean temperature of 28.4 deg C. 

Singapore experienced, on average, one to two heatwaves per decade. 

A heatwave in Singapore is defined as three consecutive days when daily maximum temperatures are at least 35 deg C. The daily mean temperature during the period should be at least 29 deg C.

Cause

Singapore does not have large-scale high pressure systems, but localised systems can still produce heatwaves, said Prof Wang.

The 2016 heatwave was due to a natural climate phenomenon called El Nino, which brings warm and dry conditions.

More frequent and extended heatwaves with higher extreme temperatures are expected to hit South-east Asia as the world warms, said director Benjamin Horton of Nanyang Technological University's Earth Observatory of Singapore.

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