SINGAPORE – Heatwaves are predicted to become more frequent and intense in East Asia with climate change, increasing the risks to human health and agriculture and creating an urgent need to develop strategies to adapt, scientists said in a recent study.

Heatwaves have been growing in severity and regularity worldwide, and a team of international researchers – led by Professor Kyung-Ja Ha from Pusan National University in South Korea – wanted to analyse the prevalence of two types of heatwaves in East Asia: hot and dry as well as moist and high humidity.

The idea was to figure out the areas most vulnerable to both types and investigate the likely impact of climate change in the coming decades.

“Heatwave events will become a much more common phenomenon in a warmer climate. And heatwaves have a devastating impact on human life, agriculture and water resources,” Prof Ha told The Straits Times.

“Identifying vulnerable regions can assist governing bodies in developing strategies that will mitigate the impacts of severe heatwaves.”

Using historical climate data, the team determined for the first time how and where these two types of heatwaves form and also predicted their occurrence in future under different greenhouse gas emission scenarios.

Dry heatwaves are characterised by stable, hot and sunny conditions with low humidity. Moist heatwaves are often accompanied by very oppressive, humid conditions during the day and night, with heat trapped by clouds.

“We know hot and humid events can be more dangerous than hot and dry events,” Prof Ha said, adding that hot and dry events have a substantial effect on water resources and agriculture.

Temperatures of 35 deg C and above, when twinned with high humidity, are especially dangerous for people because the body is unable to lose heat easily, increasing the chances of heat stress or heat stroke.

According to the study, dry heatwaves occur mostly in north-western East Asia, mainly adjacent to desert regions in parts of northern China and Mongolia, while moist heatwaves are prevalent over southern East Asia, mainly southern China and Indochina.

Based on historical data from 1958 to 2019, heatwaves of both types were observed to have intensified in duration and frequency over the past 60 years.

In their study, published in journal npj Climate and Atmospheric Science, the team defined dry and moist heatwaves as those having relative humidity below 33 per cent and above 66 per cent, respectively.

Using computer model projections, the team found that heatwaves will become more frequent and longer lasting across East Asia in future, even if greenhouse gas emissions were kept to a minimum.

If such emissions keep rising, the heatwaves would increase in severity.