Tropical Cyclone Size and Climate Change

21 11 2017

Dale C. S. Destin |

This is a continuation of our series – Tropical Cyclones and Climate Change – TCs (tropical depressions, tropical storms, hurricanes). In our previous blog in this series, we looked at Tropical Cyclone Rainfall Rates and Climate Change. In this blog, we will look at whether climate change is having an impact on TC size.

The soon ended 2017 Atlantic hurricane season has produced 17 named storms – five more than the average or 42% more than usual. This is still the most since 2012, when 19 formed. Meanwhile, there have been 10 hurricanes – four more than the average or 67% more than usual. This season remains tied with 2010 for the most hurricanes since 2012. The number of major hurricanes remains unchanged at six – three more than average or twice the usual amount. This is the most major hurricanes since 2005.

Have TCs size increased?

The Intergovernmental Panel on Climate Change (IPCC) is silent on this question. Further, the research on TC size has been quite few and the datasets very limited; however, the current answer is likely no based on available data.

Studies have shown that the size of TCs varies within and across ocean basins. Generally, the size of TCs increases with the increase in latitude or as you move poleward. For the Atlantic, this means that they generally increase in size as you go northward.

Hurricanes Katia (left), Irma (middle) and Jose (right)

Hurricanes Katia (left), Irma (middle) and Jose (right). All three were small hurricanes in terms of the extent of the hurricane and storm winds from their centres.

The initial size of a TC is also indicative of its eventual size when it reaches the maximum intensity. The rate of growth is largest at intensification.

There appears to be a trend toward smaller TCs in most ocean basins that they do form over; however, this trend is not deemed to be significant globally or regionally.

While there appears to be a negative trend in most ocean basins, no significant trend in size have been detected globally or regionally. However, the confidence level of this finding is considered relatively low since the dataset used is relatively short and somewhat subjectively obtained.

Will TCs increase in size in the future?

Although some studies have indicated a decrease in size, it is not clear how size will change in the future with a warming climate. The increase in intensity could be theorized to have both a positive or negative trend on size.

More intense TCs could mean higher pressure gradients due to a tightly ‘rap’ system and no change in central pressure, in that case, the trend in size could be toward smaller systems. On the other hand, if cyclones exhibit lower central pressure, then the trend in size could be toward larger systems. Much more research is needed in this area.

There are lots of talk in the press about TCs becoming larger due to climate change; however, there is no clear evidence to support this claim. There are two main scientific papers that address this matter – one found that the size is decreasing and the other said that the size will increase. However, both papers agree that no change in size has yet occurred due to climate change.

Our next blog in this series will look at the impact, if any, of climate change on tropical cyclone duration.


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