Amid the COVID-19 pandemic, researchers from around the world gathered virtually in July for a joint conference of the Japan Geoscience Union and AGU (JpGU-AGU Joint Meeting 2020), and one topic they discussed is of critical importance to the region: the growing threat from typhoons as the planet heats up.
Typhoons and hurricanes are one of the drivers of intensifying natural disasters, which in 2019 caused some $150 billion in damages around the world, according to the insurer Munich Re. It was a consecutive year of record losses from typhoons in Japan, which suffered $17 billion in damages in the wake of Typhoon Hagibis, 2019’s costliest event. Researchers are trying to understand how and why typhoons are becoming more ferocious in the region.
More Storms Landing in China
In a long-term study that was the basis for a poster submitted to the conference, scientists found that severe typhoons making landfall have increased abruptly in China since 2004. The researchers analyzed tropical cyclone data from the China Meteorological Administration’s Shanghai Typhoon Institute for the July–September period from 1973 to 2017. They showed that about 9.7% of landfall typhoons in southern China underwent a rapid intensification in the 24 hours before coming ashore during the 2004–2017 period, more than double the 1.6% and 3.1% intensification over the previous periods. Citing previous research exploring the relationship between more intense typhoons and global warming, the scientists noted that overall, warmer oceans are driving such storms, whereas warmer land surfaces in southern China are helping attract them.
“The intensifying typhoons are controlled by several factors,” said study coauthor Zhixiang Xiao of the Guangxi Institute of Meteorological Sciences. “However, our results show that the warming ocean, especially the warming northern South China Sea, benefits typhoon enhancement before landfall.”
Because of the complexity of the various interacting systems at play, Xiao said that it’s very difficult to make predictions that could result in better policy making to mitigate storm impact and suggested that computer simulations using deep learning techniques could be more effective than traditional prediction methods.
Rising Super Typhoons
Researchers in Taiwan, meanwhile, looked at how super typhoons, which have average maximum wind speeds of over 209 kilometers per hour, or 113 knots, are increasing in the northwest Pacific. In a study submitted to the conference as a poster, the researchers used satellite infrared imagery and wind vector plots for each typhoon and considered environmental factors that can strengthen such storms.
They found that southwest airflows and northwest cold air masses play crucial roles in strengthening super typhoons in summer and winter, respectively; southwest air flows also boost most winter super typhoons as well, making them more intense than their summer counterparts. The scientists noted that the period 2013–2016 had the highest average number of super typhoons per year at seven, with nine in 2015, second only to 11 in both 1965 and 1997.
“The increasing strength of typhoons in the Northwest Pacific Basin in recent years is in response to global warming,” study coauthors Yuei-An Liou, a professor at the Center for Space and Remote Sensing Research at Taiwan’s National Central University, and Ravi Shankar Pandey, a Ph.D. student, said in an email. “This issue needs proper attention to mitigate the risk involving them in the region.”
Scientists in South Korea also called for further research to cushion typhoon blows, particularly for storms that come relatively late in the season. In a conference poster based on 65 years’ worth of data, researchers at Inje University in South Korea found the frequency and intensity of typhoons affecting the Korean Peninsula in September and October, known as autumn typhoons, have been increasing. A study of typhoons from 1954 to 2019 using statistical analysis and numerical modeling showed that five of the eight October typhoons to affect the peninsula since 1954 occurred from 2011 to 2019; three of Korea’s seven typhoons in 2019 occurred in September and caused significant damage.
Typhoons’ maximum instantaneous wind speeds, a driver of wind damage, were also up. The researchers attribute this increase to rising sea surface temperatures (SSTs) in the northwest Pacific, noting that regional SSTs are increasing faster than the global average and that SSTs remain high around Korea in September and October. But they also said a hypothetical storm approaching the peninsula in October will not weaken, which was the case in the past, because while the land begins to cool, the sea remains warmer longer.
“This will develop into a powerful typhoon due to the greater temperature difference around the Korean Peninsula, which lies on the border between the cold continent and the hot sea,” said study coauthor Woo-Sik Jung of the university’s Department of Atmospheric Environment Information Engineering. “In other words, the larger the temperature difference, the stronger the wind, the more powerful the autumn typhoon around the Korean Peninsula can be compared to the summer typhoon.”
One scientist based in Japan who was not involved in these studies said there’s conflicting findings from research about whether the number of typhoons is increasing or decreasing amid climate change.
“However, most studies have shown that the typhoon intensities in terms of wind and rainfall would increase under global warming,” said Sridhara Nayak of the Disaster Prevention Research Institute at Kyoto University, who participated as a convener for a session on extreme weather events at JpGU-AGU Joint Meeting 2020. “So the super or severe typhoons are expected to occur in the future warming climate, which would bring much stronger winds compared to present typhoons and heavy rains to the landfall region and would be a more severe threat to human life and property.”
—Tim Hornyak (@robotopia), Science Writer