“The wet-bulb temperature is the lowest temperature that can be reached by water evaporation alone under current ambient conditions,” said study co-author Wang Fan, a doctoral student at Hong Kong Baptist University and visiting student at Harvard University.
Wang said the higher the actual vapor pressure, or the amount of water vapor in the air, the harder it is for water to evaporate.
Last year was the hottest year on record, with July being the hottest month ever, with the global monthly average temperature reaching 1.5 degrees Celsius above pre-industrial levels.
And the situation is set to get worse, the team writes, as the global increase in wet-bulb temperature over the past few decades is projected to continue due to a warming climate, particularly in the tropics and mid-latitudes, where about half the world’s population lives.
02:04
Relative humidity in southern China reaches 100%
Relative humidity in southern China reaches 100%
Researchers from Baptist University, the University of Science and Technology of China, and Harvard University looked at observation stations across China from 1979 to 2018 and found that the rate of increase in wet-bulb temperature was higher than expected in northern China during this period.
“The different trends in humidity levels between northern and southern China are attributed to faster warming in high latitudes of East Asia as a result of global climate change modulating large-scale atmospheric features,” Wang said.
“As a result, moisture transport from the South China Sea to southern China is suppressed, while moisture transport from the Pacific Ocean to northern China is accelerated.”
Wang said that by the end of the century, the wet-bulb temperature in southern China could rise by 5 degrees, and by a further 2 to 3 degrees in the north.
03:45
Deadly heatwave hits South and Southeast Asia
Deadly heatwave hits 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 temperatures but also rose most rapidly. Other major urban areas, such as the Yangtze River Delta and Sichuan Basin, also “showed a significant upward trend,” the team wrote.
“Furthermore, we found that widespread and uniform high heat stress is likely to occur across the eastern part of China, where 94 percent of the country’s population lives. [by] “By the end of this century,” the team said.
“Our findings highlight the need to develop adaptation measures and invest in renewable energy to avoid the adverse effects of heat stress in eastern China,” the researchers said.
“Policymakers will come under increasing pressure to take measures to mitigate these impacts and protect local communities from the negative consequences,” Wang said.
Because wet bulb temperature involves both temperature and humidity, preparing for it needs to go beyond general heat mitigation strategies to also include measures to reduce humidity levels, he said.
Wang said this could include “increasing ventilation, using dehumidifiers and designing buildings to improve air circulation.”
