Tropical cyclones can cause devastating and lethal damage to East and Southeast Asian countries. But accurately tracking changes in the frequency and intensity of typhoons is challenging in part because the data on these storms hasn’t always been consistently kept, and in part because there’s simply a lot of variability in the number of storms that make landfall.

In a recent issue of Nature Geoscience, new cluster and bias-corrected analyses of storm data show that the intensity and frequency of these dangerous storms have increased considerably. This increase is most likely due to oceanic warming related to climate change.

The authors of this paper focused on typhoons that strike East Asia, which limits the analysis to the northwest Pacific Ocean. They used a regional cluster analysis to probe the storm data, grouping the cyclones according to the part of the ocean where they formed and their movement patterns. This clustered analysis allowed the researchers to organize the inconsistent data in a way that allowed them to make inferences despite data variability.

The analysis showed that the frequency of typhoons that make landfall has increased 12 to 15 percent in the last 37 years. In addition to the increase in typhoon frequency, there has been a marked and significant increase in Category 4 or Category 5 storms, which are the most dangerous and deadly. This doesn't mean that the number of storms increased, just that more of the storms that made landfall were strong enough to be rated typhoons.

Having seen this increase in dangerous storms, the authors examined changes in sea surface temperature, which can feed energy into storms. They hypothesized that a relationship exists between the increase in storm intensity and human-driven oceanic warming. When looking at the four clusters of storm data separately, they saw that the two clusters of storms that form in regions with more pronounced oceanic warming saw steeper increases in both frequency and intensity.

Storms that form off the coast of East Asia and Southeast Asia have large and robust increases in both frequency and duration, whereas the rate of change for storms that form in the open water, far from the coast, is more modest. These data also seem to show that the increase in severe tropical cyclones is related to locally enhanced warming of the ocean adjacent to East Asia and Southeast Asia.

When changes in storm frequency and intensity over time were compared to the changes in ocean surface temperature over time, the authors found that the intensity curve for storms closely matched the warming curve for oceanic temperatures. The authors suggest that this increase in storm intensification may be because a warmer ocean diminishes the negative feedback that is otherwise caused by the typhoon mixing the surface with cooler upper-ocean waters.

The exact role of climate change in storm strength has been met with controversy. Although continued warming is almost certain to affect future storms, identifying a clear effect in past data is often difficult, largely because weather events like storms have an inherent degree of randomness.

Because they analyzed data from several different tropical cyclone data sets, the authors feel confident in the robustness of their findings. Despite inconsistencies, the data all led toward the same conclusions. This link between oceanic surface temperature and increase in typhoon intensity will likely provide important information that researchers can incorporate in climate and weather models, hopefully helping with severe weather preparedness and anticipation.

Nature Geoscience, 2016. DOI: 10.1038/NGEO2792 (About DOIs).