GEOGRAPHY

Super typhoon season ahead of the 21st century? Or related to global warming


Since July, after the “Teli” began the typhoon season, “Sula” just left, “sea anemone” connected, and then “little dog” again, since the beginning of this year, more than ten typhoons have formed in the northwest Pacific and the South China Sea, although the number of typhoons that landed in China is small, but the intensity is strong, the path is complex, the impact range is wide, and the risk of disaster is high.

For example, Super Typhoon Du Surui, which made landfall in Fujian in July this year and then went north, brought extreme rainstorms and serious disasters to many parts of China.

Super typhoons tend to be most frequent in autumn, why do they appear in summer? Recently, the latest research results of Yu Xiping, Chair Professor of the Department of Marine Science and Engineering of Southern University of Science and Technology, and several collaborators from Tsinghua University, Ocean University of China and the University of Hawaii, were published in Nature. They found that since the 21st century, super typhoons around the world have shown a significant phenomenon of early season, and proved that global warming is the main driver of this phenomenon.

Research diagram Courtesy of SUSTech

“August and September are the typhoon season, and we find that the occurrence of super typhoons shows a seasonal trend. According to the statistical pattern of multi-year averages, super typhoons are most frequent in autumn, but in recent years, super typhoons are increasingly occurring in summer. Yu Xiping, the corresponding author of the paper, pointed out.

The reviewers pointed out in their comments that the work found that the season of super typhoon occurred earlier, and this phenomenon showed a significant statistical trend in the world and individual sea areas, and super typhoons are closely related to social life, which enriches the research system for detecting changes in super typhoon activity and has great significance for the wider community.

The global trend of super typhoons is seasonally advanced

Tropical cyclones, also known as hurricanes or typhoons, are among the most devastating natural disasters. The maximum wind speed of super typhoons (strong tropical cyclones) can exceed 60 meters per second, and the wind force reaches more than 16, causing extremely serious impacts on human society and the natural environment.

Over the past few decades, typhoon activity around the world has changed significantly, including an overall increase in typhoon intensity and a frequent number of super-strong typhoon events. These changes have had a profound impact on the sustainable development of affected regions around the world.

In the study, the team found that since 1980, the occurrence of super typhoons has been seasonally earlier. “Our study found that super typhoons occur 3.7 days earlier every decade in the northern hemisphere and 3.2 days earlier in the southern hemisphere.” Yu Xiping, the corresponding author of the paper, introduced.

This seasonal progression is evident in all ocean basins, with the strongest trend in the western North Pacific, where tropical cyclones occur most frequently. It is worth noting that the season of super typhoons is noticeably advanced, but weak typhoons are not.

For example, Typhoon Du Surui, which occurred in July this year, had a serious impact on the Beijing-Tianjin-Hebei region. “We found that the risk of compound disasters in the event of extreme rainstorms caused by summer winds is greatly increased when super typhoons move from autumn to summer, which is strong evidence in South China and the Gulf of Mexico in the United States.” Yu Xiping said that the devastating impact of such composite disaster events far exceeds that of any single disaster event, bringing great challenges to the existing disaster prevention and mitigation system.

Greenhouse gas emissions are the main cause

Today, global climate change has become one of the biggest challenges facing the world, and global warming caused by greenhouse gas emissions has led to a series of serious problems such as rising temperatures, increased extreme weather events, and rising sea levels.

The research team further explored the reasons for the early super typhoon season and found that global warming played a leading role in the early super typhoon season.

“Rapid typhoon intensification is a super-strong typhoon and is a key physical process that distinguishes it from other weak typhoons. Super typhoons typically undergo a rapid enhancement process at least once during their lifetime, with maximum sustained wind speeds increasing by 18 meters per second in 24 hours. Through the results of data analysis, we confirmed that the rapid strengthening process of typhoons also showed a significant seasonal advance trend. Shan Kaiyue, the first author of the paper and a postdoctoral fellow in the Department of Water Conservancy of Tsinghua University, introduced.

After comprehensively analyzing the characteristics of rapid typhoon intensification and seasonal changes of ocean elements, the research team found that there was no obvious seasonal change in atmospheric factors conducive to rapid typhoon enhancement, while marine factors such as typhoon potential intensity and ocean heat content closely related to SST showed significant seasonal advance.

In order to clarify the relative contribution of human activities to the natural variability of the climate system in the phenomenon of seasonal advance of the above ocean elements, the research team used the latest climate models to analyze the relative contribution of greenhouse gases, anthropogenic aerosols, volcanic eruptions and solar activities, and found that the warming of the global climate system caused by human greenhouse gas emissions played a leading role in the advance of the super typhoon season.

“The study not only reveals the existence of early trends in the super typhoon season, but also provides a new perspective on the risk assessment of associated composite disaster events, especially in estuarine areas where storm surges and watershed flooding caused by super typhoons are likely to occur.” Yu Xiping said that this will help improve the early warning and response capacity of such complex disaster events, and ultimately help guide the development of disaster emergency management and mitigation strategies. (Source: China Science News, Diao Wenhui, Liao Yang)

Related paper information:https://www.nature.com/articles/s41586-023-06544-0



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