Explainer: What is causing heatwaves around the world and will Singapore be affected?

SINGAPORE — Countries across the world are suffering from one of the hottest summers in history, with the mercury hitting unbearable levels in areas where many are not prepared for such extremities. 

This has led to countries, including China, France and the United Kingdom to issue warnings to their citizens to avoid staying outdoors.  

TODAY spoke to experts to find out what is causing these heatwaves, how climate change has played a part in their occurrences and whether Singapore will have to brace itself for warmer weather. 

WHAT IS CAUSING THE HEATWAVES? 

A heatwave is defined as an extended period of hot weather where temperatures are above the historical average in an area for two or more days.

It is a weather phenomenon that occurs when high pressure in the atmosphere moves in and pushes warm air downwards.  

That air warms up further as it is compressed and people begin to feel a lot hotter.

Professor Benjamin Horton, director of the Earth Observatory of Singapore at Nanyang Technological University, said that the high-pressure system pressing down on the ground expands vertically, forcing other weather systems to change course, which result in a reduction of wind and the presence of clouds in the area. 

This makes the air become more stifling, he added.

Dr Wang Jingyu, an assistant professor at the National Institute of Education whose research interests include climate modelling and land-atmosphere interaction, explained: “The air cannot escape this ‘heat dome’ because of the high pressure. This 'heat dome' acts like a lid on a pot and traps heat from escaping.” 

The abnormally high temperatures in Europe this year are due to a high pressure system called the Azores High, which usually sits off the coast of Spain.

However, it has grown larger and pushed farther north this summer, bringing higher temperatures to France, the Iberian peninsula that includes Spain and Portugal, and the UK.

Dr Wang said that climate change has increased the frequency of an "extremely large" Azores High occurring — from once every 10 years in the pre-industrial period to once every four years in the 21st century.

The heatwaves now plaguing Asian countries such as China and Japan are also affected by a similar high-pressure system called the West-Pacific Subtropical High, which is located over the Tibetan Plateau and North Pacific Ocean. 

“Unfortunately, this system is also abnormally strong this year due to climate change, which creates the heat dome over the majority of East Asia, causing unprecedented heatwaves,” Dr Wang added. 

Experts said that climate change has affected high pressure systems across the globe, which in turn cause more severe and frequent heatwaves.

WHAT ARE THE DANGERS OF HEATWAVES? 

Extreme heat can cause lower blood pressure that, coupled with perspiring, can lead to heat exhaustion. 

Symptoms include nausea, dizziness and fainting. If one's blood pressure drops too far, the risk of heart attack also rises. 

The intense and prolonged heat not only poses a risk to human health, but to infrastructure as well, especially in countries that do not often experience such extreme heat. 

Associate Professor Koh Tieh Yong, a weather and climate scientist at the Singapore University of Social Sciences (SUSS), said: “Infrastructure everywhere is designed to withstand a range of environmental conditions based on historical climate records. So they are expected to handle extreme conditions only rarely. 

“But as the climate changes, heatwaves become more frequent in temperate countries and push the limits of the infrastructure to tolerate hot temperatures.” 

This means that governments need to carry out maintenance works more often until old infrastructure is renewed with tougher tolerance parameters.

HOW HAS THE HEATWAVE AFFECTED COUNTRIES? 

UNITED KINGDOM 

For the first time in the UK, temperature forecasts have hit 40°C — an all-time high — prompting the Met Office, the national weather service, to issue its most severe warning in anticipation of rising temperatures.  

Network rail, the UK's national rail service, has started enforcing railway speed restrictions across most of England and Wales, with trains mostly limited to speeds of 90mph (144km/h), down from 100mph, while some trains will be made to go as slow as 20mph to avoid overheating the tracks, British news media BBC reported recently.

This is because rail temperatures can be up to 20°C hotter than the air, and extreme heat can cause them to buckle. 

To avoid this, workers have painted certain railway tracks white to help reflect sunlight, with the hope of reducing temperatures by up to 5°C.

Such measures, however, have resulted in major train delays and cancellations across the country. 

CHINA

In China, extreme heat has caused roads to buckle and roof tiles to melt. 

News agency Reuters reported that there were state television reports showing a section of a road in a town in Southern Jiangxi province arching up at least 15cm. 

In another report by the New York Times, a museum in Chongqing displaying imperial relics from the Palace Museum was closed for repairs, after its roof tiles melted as extreme heat had dissolved the underlying tar. 

By 3pm on July 12, 86 cities in the country had issued red alerts — the highest in a three-tier warning system for extreme weather, Reuters reported. 

FRANCE 

High temperatures in France have led to wildfires in its southern region during recent weeks.

More than 10,000 hectares of vegetation were destroyed by fires in the Gironde region last Saturday and more than 14,000 people were evacuated from the area since Tuesday, the local authorities said.

SHOULD SINGAPORE AND SOUTHEAST ASIA BRACE FOR WORSE WEATHER? 

Singapore and Southeast Asia seem poised to avoid sudden spikes in temperature during this period.

Assoc Prof Koh from SUSS said: “Southeast Asia lies within the tropics where the weather works differently. The mentioned pressure systems do not affect us directly.” 

Instead, the weather in this region is influenced by tropical ocean-atmosphere interactions such as El Nino and La Nina, which refer to the warming and cooling of sea surface temperatures respectively.

Although the region will not experience sudden spikes in temperature now, the occurrences of heatwaves will become more common in the future due to climate change. 

Prof Horton from the Earth Observatory of Singapore said: “More frequent heatwaves, longer heatwave duration, and higher extreme temperature during heatwaves will occur over the entire Southeast Asia in a warmer world.

“These changes mean that a rare heatwave, such as that occurring once-in-50-years in the current climate, will become common and happen more frequently in a warmer future.”