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Tuesday, 24 January 2012

Canadian Weather that Kills – how do various extreme events stack up?

Achy joints in cold damp weather?  Headaches when the wind blows?   Sometimes it seems that popular beliefs regarding our wellbeing and the weather are better developed than rigorous medical evaluations.  If there is something that Canadians can agree upon, we have no shortage of weather to open conversations with.  It should not be surprising that the most visited website in Canada is the official weather site of the Meterological Services of Canada Weather office

We do know that heat can kill, so can cold.  Floods, lightening strikes, tornados, hurricanes and other extreme weather events are notorious for racking up mortality statistics, and presumably related morbidity.   There are other issues that are weather related like avalanches, ultraviolet light exposure and air quality that also contribute to our wellbeing. 

We spend a substantive budget on weather forecasting and reporting, for which there are some 1 ½ Million forecasts issued every year.  With that comes some 15000 severe weather warnings, in part designed as a way for individual Canadians to make healthier choices.  So the question that is seeking an answer, is which of these risks is likely the most concerning.   It appears that while some attempts have been made, none are public since the approaches used vary from counting bodies to sophisticated Poisson regression techniques with define lag times.  

Here goes an attempt, from least to most, and an invitation to readers to contribute to helping define weather attributable mortality in Canada (please either post a comment or send to drphealth@gmail.com).  

Weather condition
Estimated annual deaths
Annual rate of about 2 deaths
Natural Resources Canada reports 195 deaths over 168 flooding disasters for the 20th century
Lightening strikes
Excellent data provide an annual national incidence of 0.11 deaths per Million population
Average of 14 per year
Excellent statistics of 329 deaths over 30 years.  An extreme 1910 avalanche in Rogers Pass killed 62
Extreme episodic events – tornados, floods, etc
Average difficult to determine, likely <20.  Even the extreme events are <100.
Annual incidences vary widely.  The most tragic events in last 100 years:   Hurricane Hazel - 1954, 81 deaths, Escumina hurricane 1959 – 35 deaths; 1998 Ice storm – 28 deaths ;  Regina tornado 1912 – 28 deaths, Edmonton tornado 1987 – 27 deaths,
UV exposure
Based on all melanoma deaths and not attributing any to tanning salons
Several studies have estimated excess deaths in Toronto at ~120 per year and Vancouver ~20 per year.   Using these as an incidence provides a rough estimate nationally.
The toughest estimate to obtain but the impact is likely in the order of several times the number of deaths caused by heat.  UK estimates put the heat:cold mortality ratio near 10 times.  A gross analysis of the number of excess deaths during winter months will provide an estimate of about 5000 excess deaths for Canada annually.
Air pollution
Health Canada estimates of about 4000 while the Canadian Medical Association has issued an estimate of 20,000.  Estimates are based on times series regressions linking mortality databases with air pollution monitoring data

Were you surprised given our high attention to extreme weather events, avalanches and even heat based events?    More on air quality in a future posting.  

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