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Severe weather to increase in frequency & intensity: AIR Worldwide

30th June 2017 - Author: Staff Writer

Catastrophe risk modeller AIR Worldwide compiled the latest findings of climate science in a report on the potential impact of climate change to extreme weather; bringing attention to tropical cyclones, extratropical cyclones, severe storms, wildfire, and floods and warning of an overall increase in frequency and intensity of severe weather phenomena globally.

Hurricane image from the Space StationRegulators and rating agencies have begun to require firms to incorporate impact of climate change into policies affecting decision-making processes – contributing to an increased focus in the insurance world to climate change impact on variability of severe weather.

Dr. Peter Sousounis, assistant vice president and director of meteorology at AIR Worldwide, said; “Many in the insurance world are paying increased attention to climate change in light of reports of increasing variability of atmospheric perils such as windstorms and floods.”

“As a result, clients have asked AIR to keep them apprised of the current state of the science regarding climate change impacts on extreme weather.”

The AIR report presents the latest findings from the scientific community about how climate change is likely to impact the characteristics of some key weather phenomena, however, the authors reiterated that projections of how climate warming will affect severe weather patterns are notoriously difficult to predict and subject to multiple variables in both the atmosphere and impact of human activity such as emissions levels.

The findings indicate that by the end of the 21st century, global surface temperatures will likely increase by a few degrees Celsius.

However, the speed of this climate warming will not be regionally uniform or see linear inter-annual progression;  “due to the geographic variability in the climate response and to the presence of internal variability, warming (and changes in other climate variables).”

The net result of earth surface warming will be an increase in the inherent convective instability of the atmosphere; thermodynamic instability from a combination of surface warming and cooling or less warming at upper atmospheric levels – especially at mid latitudes – and this is expected to increase the frequency and intensity of severe weather events.

Overall, the weather risk showing the strongest evidence to increase in severity, is inland and coastal floods; this is down to climate change induced heavier precipitation causing river overflow and rising sea levels threatening coastal areas.

Cyclones are a peril forecast to show a more unusual pattern, as climate change is expected to decrease amounts of cyclones, but increase cyclones in the “strong to extreme” category.

The report explains this could be due to tropical cyclones (TCs) deriving their energy from latent heat acquired from evaporation of water at the ocean surface that is “subsequently released upon condensation at greater heights.

“With a weaker ambient horizontal temperature gradient, there will be fewer opportunities for storms to initiate development.

“However, once they do, other processes that complement baroclinic development, such as latent heat release, will lead to considerable intensification.”

“At a global scale, Holland and Bruyère (2014) estimate that the proportion of Category 4 and 5 storms has increased over the last several decades by ~25‐30% per degree of warming.”

Wild fire is another peril forecast to increase across the globe as the earth gets hotter and drier and precipitation levels change patterns.

Canada, which recently suffered one of its most extreme wildfire events in history in Fort McMurray, is forecast to see a stark increase in fire risk;  “Findings from the CGCM1 showed an increase in fire risk almost everywhere across Canada—with highest increases in eastern Manitoba, western Ontario, and western Northwest Territories.

“The increased risk was almost equally from Climate Change Impacts on Extreme Weather 35 increases in lightning and human cause. Overall, the average increases were approximately 75%, but some places in the areas of highest risk showed over 100% increases.

“Findings from the HadCM3 also showed increases that were generally twice those from the Canadian Model, but the highest risk areas were southern British Columbia, central Ontario, and central Quebec. Moreover, the majority of increases were from lightning rather than human cause. ”

Western Europe, (British Isles, France, and Portugal) and the U.S. Northwest Pacific coast are projected as being vulnerable to an increased risk from an extratropical cyclone-induced storm surge, with areas lacking existing infrastructure, such as sea walls, at significantly higher risk.

The report said Europe had already witnessed an increase in frequency and intensity of heavy precipitation events “while in other continents the trends are less clear, perhaps reflecting data availability or limited analysis (Collins et al. 2013).”

The overall trend observed is for precipitation to increase in areas where precipitation already occurs with some relative frequency, the report said, signalling the potential for both increased loss frequency and severity for the insurance and reinsurance industry.

However, areas with infrequent precipitation are likely to see even less: “Areas of significant precipitation reduction are fewer: parts of western Canada, equatorial Africa, eastern Asia, and eastern Australia.

Asia has seen “statistically significant decreases of precipitation in southwest, central, and northeast Asia; and statistically significant increases of precipitation in northwest and southeast Asia during the period of 1978 to 2002.”

The AIR report also underlined and explained the U.S.’ particular vulnerability to severe weather events; “Geography also plays a role in generating preferred environments. One of the reasons the United States has the highest probabilities of severe weather has to do with the country’s geography.

“The Gulf of Mexico is the primary source of warm moist unstable air for the Great Plains. As low pressure systems develop on the lee side of the Rocky Mountains, southeasterly winds ahead of the low draw the warm moist unstable air northwestward.

“At upper levels, strong southwesterly winds bring air from the Mexican Plateau, which is much drier and cooler. This configuration creates both a thermodynamically unstable environment as well as one with both wind speed and directional shear.”

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