Calm before the Storm?

Climate change gets a lot of attention in the media, and it is easy to start believing every extreme weather event is caused by global warming. The media hype can also lead one to conclude that extreme events are getting more frequent and more severe. If that is true, perhaps Canada will start seeing more losses from hurricanes.

Historically, Canada has not been significantly impacted by North Atlantic hurricane activity. On a few rare occasions, fast-moving hurricanes – the Great New England of 1938 and Hazel of 1954 – have tracked into Canada with wind speeds high enough to cause power outages and some damage to trees and small structures.

Neither of these storms produced strong hurricane force winds in Canada, but Hazel caused devastating floods in and around Toronto and still ranks as one of Canada’s greatest natural disasters.

Hurricane Hazel made landfall as a Category 4 storm in the United States about 10 miles north of Myrtle Beach, South Carolina – far from the Canadian border. However, because of its very fast forward speed – nearly 50 miles/hour (mph) – the storm was able to travel hundreds of miles across the mid-Atlantic states without losing hurricane strength.

The storm would likely have weakened to tropical storm status before entering Canada, but while over Pennsylvania, Hazel interacted with another storm system – a strong cold front – that enabled it to maintain hurricane strength as it crossed over the Great Lakes and into Ontario.

The combined storm system then stalled over Toronto as a Category 1 hurricane, dumping several inches of rain on the city. Exacerbating the situation was the fact that the Toronto area had experienced unusually high rainfall amounts in the weeks before Hazel’s arrival, so the ground was already saturated. The record amount of rainfall that fell as a result of Hazel ran directly off the surface and into the area streams and rivers, causing all of the major rivers in Toronto to overflow their banks.

There were 81 fatalities in Canada as a result of the storm and unprecedented devastation. Along with homes and commercial structures, roads and infrastructure were washed out. The cost and economic damages of Hazel occurring today are estimated to be well over US$1 billion.

FREQUENCY AND SUSCEPTIBILITY

Could the changing climate make events like Hazel more frequent in Canada in the future? Is climate change making Canada more susceptible to hurricane damage?

As indicated earlier, many people may think hurricanes are already becoming more frequent and severe. It would be surprising to learn that is not the case.

The Intergovernmental Panel on Climate Change (IPCC) collects and synthesizes the global research and scientific consensus on climate change and its many potential impacts. IPCC’s most recent report in 2013 shows that climate change has not had an observable impact on hurricane activity to date.

Ability to observe activity

The apparent increase in tropical cyclone activity in the North Atlantic is, in reality, simply a result of the ability to observe more of that activity. That is, advances in technology over the past several decades have enabled scientists to detect and track more storms. And after adjusting for advances in detection technology, the scientific consensus is that there is no statistically significant increasing trend in tropical cyclone frequency.

Scientists also generally agree that demographic changes have accounted for the upward trend in hurricane losses to date, with the increasing numbers and values of properties constructed in areas prone to catastrophes being the primary driver of increasing losses. Notes the IPCC report, “There is low confidence in any observed long-term increases in tropical cyclone activity (intensity, frequency, duration) after accounting for past changes in observing capabilities.”

Future developments

What about the future? Perhaps, again surprisingly, the current scientific consensus is it is likely the global frequency of tropical cyclones will either decrease or stay the same with climate change. This counterintuitive conclusion is a result of the complex interactions and feedback loops in the atmosphere.

For example, while rising sea surface temperatures (SSTs) have a positive impact on tropical cyclone formation, higher SSTs also create more instability in the atmosphere, most notably, more vertical wind shear. Wind shear is the difference in wind speed and direction between winds in the upper atmosphere and at the surface – a detrimental factor for storm development.

While tropical cyclone frequency is likely to either stay the same or decrease on a global basis, the IPCC reports, the maximum intensity of hurricanes is likely to increase by the end of this century. The IPCC’s projected range is for peak wind speeds to increase from 2% to 11% over the next several decades.

If peak wind speeds do increase, more storms could make their way into Canada and make some areas of the country more vulnerable to hurricane damage – from both wind and rain.

HIGH WINDS, BIG POTENTIAL LOSSES

While 2% to 11% does not sound like a significant increase, hurricane damages increase exponentially with wind speeds. Studies by Karen Clark & Company (KCC) show that a 2% increase in maximum winds will lead to a 15% increase in insured losses, while an 11% increase in wind speeds will lead to a doubling of losses.

Increasing wind speeds also mean the geographical extent of the storms will be greater and the impacted area larger. Northeast hurricanes already tend to be relatively large and fast-moving.

Consider that the Great New England Hurricane made landfall across Long Island, New York travelling at more than 50 mph. Peak sustained winds at landfall are estimated to have been approximately 120 mph, and hurricane force winds covered hundreds of square miles.

Figure 1 below shows the track and wind footprint of the 1938 event, while Figure 2 shows what the likely wind footprint would be if peak winds are increased by 11% to 133 mph.

Clearly, the hurricane will impact a much larger area – KCC estimates insured losses in the U.S. will increase from US$40 billion to over US$80 billion. More importantly for Canada, the more intense storm will likely cause hurricane force winds well into Quebec, resulting in extensive damage in Montreal.

It may be many decades before hurricanes are a serious concern for Canada, but potential losses from other perils such as floods and earthquakes continue to rise – primarily as a result of demographic factors. While there may be temporary lulls in catastrophe activity, the demand for catastrophe reinsurance will continue to increase over the long term.