Heat waves more frequent and intense, last longer

Against the backdrop of global warming, the onset of land-based heat waves around the world has significantly advanced in the 21st century, with faster development into peak temperatures. The occurrence of such weather phenomena has become more frequent, intense and persistent since 1979, according to recently published research titled "Earlier and faster heat wave onset on land under a warming climate" in the international academic journal Nature Climate Change.

The study was conducted by a research team at the South China Botanical Garden of the Chinese Academy of Sciences, in collaboration with domestic and foreign scientific institutions.

Their findings offer a new scientific perspective for improving the monitoring and early warning of extreme heat risks, the team said.

"In the past, scientists focused more on whether heat waves were becoming more frequent, stronger and longer-lasting," said Xu Wenfang, an associate researcher at the SCBG of the CAS.

"The latest research indicates that the timing and onset processes of heat waves have also changed in the past several decades," said Xu, adding that if heat waves arrive earlier and peak more quickly, the time window for society and ecosystems to prepare and adapt may be further shortened.

"It is necessary to enhance the timeliness of heat wave monitoring, warning and emergency response, and to promote the timely translation of warning information into risk management actions," she said.

The research team divided the first heat wave into three types of onset: rapid, moderate and slow, based on the relative time it takes from the beginning to reach peak temperatures each year.

From 2001 to 2023, there has been a significant upward trend in the proportion of land areas experiencing rapid onset of first heat waves relative to the total area affected by heat waves each year, indicating a new trend toward more rapid onset of land-based initial heat waves worldwide, according to the research.

"The trend implies that assessing heat risk requires not only considering how intense and how long the heat waves are, but also when they occur and how quickly they reach peak temperatures," said Xu.

Meanwhile, based on global climate data from 1979 to 2023, researchers analyzed the long-term changes in the onset and end times of land-based heat waves, the length of the heat wave season and the speed of the onset of the first heat wave each year.

The results were cross-validated by researchers after using multiple independent climate datasets, she added.

The findings show that the first occurrence of land-based heat waves worldwide has advanced by approximately 3.3 days every decade, translating to an overall advancement of about two weeks over the past 45 years.

Meanwhile, the end of the last heat wave has been delayed by about 5.4 days per decade, with a total delay of approximately 24 days over the past 45 years.

Consequently, the heat wave season has extended by about 8.7 days per decade, amounting to an overall extension of around 39 days in 45 years, according to the research.

Spatially, 72 percent of the world's land area shows a trend of earlier heat wave onsets, 79.6 percent shows a trend of delayed heat wave endpoints and 92.1 percent shows a trend of an extended heat wave season.

"Such changes are particularly pronounced in arid regions," said Xu.

The research also found that the extension of the heat wave season increases the risk of crops being exposed to high temperatures during critical growth stages, as the impact of heat waves is further extending into both the earlier and later phases of the crop growth period.

From 2001 to 2023, the proportion of land area around the world where major crops are exposed to heat waves during key reproductive stages — such as flowering and silking — increased by 1.6 percent to 13.3 percent, compared to the period from 1979 to 2000.

With the increasing frequency of extreme weather, the United Nations launched the Early Warnings for All initiative in 2022 to close gaps and protect everyone on the planet. China became the first country to answer the call, proposing an action plan in 2024 and launching an intelligent meteorological early warning solution in 2025 named MAZU.

qiuquanlin@chinadaily.com.cn