NTU HIGHLIGHTS

Prof. Chun-Chieh Wu, Department of Atmospheric Sciences

Recent research from our group sheds new light on how tropical cyclone (TC) activity over the western North Pacific would change as the climate warms. By examining multiple model outcomes under one future warming scenario, we identify a clear trend: the most intense storms—those in Categories 4 and 5—are expected to become even stronger. This pattern holds true across different sea surface temperature warming patterns and various storm track types.

Global climate models tend to underestimate how strong and how frequent intense tropical cyclones can be. To address this, we used a high-resolution "downscaling" method that combines the broad perspective of global models with the fine detail of regional models. This approach, which simulates storms at a detailed 5-kilometer scale, reveals a much sharper increase—about 12%—in the frequency of intense cyclones by the end of the 21st century. This is more than double the 5% increase suggested by global models alone. Additionally, the method shows that these powerful storms may intensify faster and could shift where they make landfall (see Figure 1).

Our analysis categorized tropical cyclone tracks into six distinct clusters, revealing two particularly important groups. One cluster includes storms that affect a wide range of coastal areas and are expected to grow significantly stronger, signaling a systematic increase in TC intensity not limited to intense storms. Another cluster features storms whose peak strength shifts northward, raising the risk of landfalls in Japan and the Korean Peninsula (see Figure 2).

To better understand these changes, we apply the Carnot heat-engine framework, which assesses TC potential using the "ventilation index"—a combined measure of atmospheric and oceanic conditions. However, seasonal average changes in this index were small or inconsistent with the observed changes in cyclone activity (see Figure 3). This suggests that the processes driving these shifts are not yet fully understood.

Looking ahead, our research will focus on how the frequency of tropical disturbances (the initial seeds of cyclones), short-term environmental fluctuations, and potential changes in cyclone structure are likely to influence storm intensity and behavior under a warming climate.