Kyoto, Japan -- Every year in the West Pacific, as summer ends and September rolls around, typhoons are not far behind. Typhoons are the most impactful extreme weather events affecting Japan and East Asia, and due to climate change, extremely strong typhoons are becoming more frequent. In order to adapt critical infrastructure to these massive storms and protect coastal areas, accurate accounting for their future impact is essential.
Assessing the disaster risks of a typhoon season involves quantitatively predicting storm intensity and frequency, relying heavily on the characteristics of regional meteorological fields and natural variability inherent in the climate system. Though varying typhoon characteristics are related to sea surface temperatures -- SST -- probabilistic evaluations that account for SST have been insufficient.
This motivated a team of researchers at KyotoU's Disaster Prevention Research Institute to analyze typhoon intensity through spatial SST patterns. They combined a slab-ocean model with the Global Atmospheric Climate Model developed by the Meteorological Research Institute of the Japan Meteorological Agency, resulting in a unique simulation that successfully represents atmosphere-ocean interactions on a global scale.
Using this, the team conducted ensemble experiments specialized for typhoon evaluation, probabilistically assessing the relationship between spatial patterns of SST in the Pacific and typhoon intensity characteristics. They performed these simulations under both historical and future conditions to assess changes while accounting for natural variability. Furthermore, they ran the experiments at both a conventional 60-kilometer resolution as well as with a horizontal 20-kilometer scale.
The team's results revealed that about 50 to 60 percent of the variance in typhoon intensity can be explained by the combination of spatial SST pattern differences and increasing average SST due to climate change. The probabilistic typhoon evaluations enabled by this study also led the team to discover that, while extreme typhoons occur once every 100 years in the present climate, they may occur four to five times per century under future scenarios.
"The impact of SST influence on the typhoon intensity in severe typhoons is clearer than we expected, as is the impact of global warming on the increase in the frequency of severe typhoons," says team leader Nobuhito Mori.
This study provides a framework for high-resolution, global-scale ensemble experiments using combined atmosphere-ocean models, reducing uncertainty in climate projections by providing a highly reliable foundation for risk assessment. These findings have particular potential for policymakers involved in infrastructure development, such as coastal protection and disaster management planning.
Next, the team intends to further refine their model to strengthen their results. "We want to understand how extreme weather is changing due to climate change," says first author Yoshiki Matsuo. "This is an important challenge from both an engineering as well as a social perspective."
