Northern China’s dry summer will be gone as climate change hits hard: study

Heat stress will become a fact of life across the country by the end of the century, with the north to see the biggest change, scientists warn

Science

Victoria Bela

Published: 8:00am, 22 Jun 2024

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Widespread heat stress will be felt by most of China’s population by the end of the century due to climate change, with the north of the country expected to be hit hardest, a study has found.

While the whole country has experienced rising heat and humidity over the last few decades, a team of researchers from China and the US found that the rates at which it has occurred differed in the north and south of China due to atmospheric features.

“The acceleration of wet bulb temperature increases in northern China challenges the conventional understanding of China’s regional summer climates, which historically categorised the south as hot and humid and the north as dry,” the team wrote in a paper published in peer-reviewed journal Nature Communications last month.

Wet bulb temperature is a measurement used to characterise extreme heat events that combines dry air temperature with humidity, which has a human health threshold of 35 degrees Celsius (95 degrees Fahrenheit), the team wrote in the paper.

“The wet bulb temperature is the lowest temperature that can be reached under current ambient conditions by the evaporation of water only,” said Wang Fan, co-author of the paper and a PhD candidate at Baptist University in Hong Kong and visiting student at Harvard.

Wang said that the higher the actual water vapour pressure – or amount of water vapour in a volume of air – the harder it was for water to evaporate.

Moist heat can hamper our ability to sweat and put us at a higher risk of heatstroke in a shorter amount of time, making elevated heat stress “a prominent global climate concern”, according to the paper.

Last year was the world’s hottest on record, with July being the hottest month as the global monthly average temperature reached 1.5 degrees above pre-industrial levels.

Unprecedented heat extremes have been occurring at a higher frequency, including a continuous heatwave in India that began in May, resulting in dozens of deaths as temperatures hit highs of 50 degrees in the capital.

And it is set to worsen, the team wrote, with the global increase in wet bulb temperature seen over the last few decades projected to continue rising due to climate warming, “particularly in tropical and mid-latitude regions, which are home to roughly half of the world’s population”.

02:04

Relative humidity hits 100% in southern China

Although southern parts of China are typically known for having more pronounced heat stress due to the lower latitude, in recent years northern China has been experiencing more extreme heat events, with the region bracing for a hotter than average summer.

The researchers from Baptist University, the University of Science and Technology of China and Harvard University examined stations across China from 1979 to 2018, and found that the north of the country had actually seen a greater rate of wet bulb temperature increase over the period.

“The distinction in the trends of humidity levels between northern and southern China is attributed to a faster warming in the high-latitude regions of East Asia as a result of global climate change which regulates large-scale atmospheric features,” Wang said.

“As a result, moisture transport to southern China from the South China Sea is suppressed, and moisture transport from the Pacific Ocean to northern China is accelerated.”

Some stations in southern China have actually experienced a decreasing trend in humidity since 1979 as a result. However, due to the widespread impact of climate warming, the entire country will be affected by heat stress.

By the end of the century, southern China could experience a 5 degree rise in wet bulb temperature, with the north facing a further 2 to 3 degree increase, Wang said.

03:45

Deadly heatwaves scorch South and Southeast Asia

During the study period, the team found that the Beijing-Tianjin-Hebei region in northern China had the lowest initial wet bulb temperature but the most rapid increase. Other major urban areas like the Yangtze River Delta and Sichuan Basin “also display distinctively upward trends”, the team wrote.

“We further find that the entire eastern China, that accommodates 94 per cent of the country’s population, is likely to experience widespread and uniform elevated thermal stress [by] the end of this century,” the team said.

“Our findings highlight the necessity for development of adaptation measures in eastern China to avoid adverse impacts of heat stress”, as well as investment into renewables, the researchers said.

As more extreme weather events occurred, it would become an issue that could not be avoided, Wang said.

“Policymakers will be under increasing pressure to take action to mitigate these impacts and protect communities from adverse effects,” Wang said.

As wet bulb temperature involves both temperature and humidity, preparing for it meant going beyond general heat mitigation strategies and including measures that reduce humidity levels, he said.

Wang said this could include “increasing ventilation, using dehumidifiers or designing buildings with better air circulation”.