Clarifications
- This story has been updated to include comment from Environment Canada on heavy rainfall events in the Windsor region.Nov 20, 2015 12:06 PM ET
"A lot of it has to do with the frequency of the storms and I think you could even extrapolate that it's got to do with climate change," ...
... "we're getting 20 times more storms now than we were 20 years ago."
However, Environment Canada says it has recently looked at the trends in heavy rainfall events and there were "no significant changes" in the Windsor region between 1953 and 2012.
It appears that the interviewee based statements on an insurance industry newsletter.
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| Excerpt. CBC response to complaint on storm statistics and frequency causing flooding. |
****** Updated Post Below *******
(Originally) no fact checkers at cbcnews.ca this week for a story on storm frequency. Hence bogus statements introduce an article on why storm damage claims are increasing:
"The more storms Mother Nature dishes out, the more problems homeowners have with their sewers and basements.
And with an increasing frequency of storm events, insurance companies serving homeowners in Windsor and Essex County are taking a harder line on what coverage they can offer and what their customers must pay to receive it."
And the interviewee seems to back this up by doubling down:
"On a statistical basis ... "we're getting 20 times more storms now than we were 20 years ago.""
Well this embodies the quote about there being lies, damn lies and statistics, because the true statistics on rainfall frequency shows the opposite in Windsor-Essex, from whence many a Tecumseth tall tale teller hail. Environment Canada statistics show us decreasing intensities - i.e., REAL downward trends in annual maxima for rainfall volumes over a range of durations from 5 minutes to 24 hours.
This data is freely available to anyone with an internet connection, and is readily applied by those water resources engineers and municipal drainage designers who work with rainfall statistics as part of their professional practice. Certainly, storms did not increase twenty times and storms cannot explain the change in insurance claims over the past decades. Storm intensities are decreasing at the Windsor Airport gauge (station ID 6139525) since the mid 1940's (CBC has clarified through Environment Canada correspondence that "there has been no significant change in rainfall events over several decades"). Other possible factors affecting damages:
1) Runoff increased due to development
2) Overland drainage systems have been compromised
3) More expensive stuff in basements
No doubt cbcnews.ca needs better fact checking (some fact checking?). There is no QA/QC in reporting on extreme weather in Canada. Sad. It took all afternoon to summarize the trends in rain intensity for climate stations across Canada in one simple graph, but its not hard to do because Environment Canada does the trend analysis on the raw data and categorizes trends as significantly significant or not in their publications - this summary of rain intensity trends is for 565 stations:
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| Real climate data from Environment Canada shows no change in historical rainfall intensities. |
The statistics for 565 weather gauges show us the following:
- there is no statistically significant change in rainfall intensity for 86% of data points
- there is a statistically significant decrease for 2 to 3% of data
- there is a statistically significant increase for 3 to 5% of data
- there is incomplete data for trend analysis 7% of the time
- for shortest duration rainfall that affects urban flooding, just less than 3% of data shows increases in intensity (5 minute intensity increases at 2.7% of gauges)
If the rainfall frequency distribution is stationary (no change), after a long, long time, half of gauges would have increases and half decreases. Looking at all data points including the non-significant trends what are the changes? :
- 41% of data showed a decrease in intensity
- 52% of data showed an increase in intensity
- 7% of data was incomplete (no data trend)
So it is not like there are a lot of increases just shy of statistical significance ... its a fairly even split for a random sample. I redid the analysis screening out rain gauge records shorter than 20 years (the data above was 10+ years) and using only gauges whose record ended in since the year 2000 to focus on newer data and more long-term reliable records. For these screened 345 gauges we find more or less the same:
- 42% of data showed a decrease in intensity
- 56% of data showed an increase in intensity
- 2% of data was incomplete (no data trend)
So has Mother Nature dished out more rain, or have developed municipalities dished out more runoff over the decades? Saying there are 20 times more storms than there were 20 years ago is just plain wrong - in fact it is a 'worse-than-useless' statement because it diverts attention from real risk factors and effective management approaches. Canada needs evidence-based policy on flood risk management and open data to support better decision making. The real Environment Canada data is available for download here:
http://climate.weather.gc.ca/prods_servs/engineering_e.html
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| Environment Commissioner of Ontario infographic non-data |
The cbcnews.ca data is available in the Government of Ontario infographic at right. Notice there is no real data there, no labels on the access, no data sources, nothing really. But it seems quite definitive with the exclamation point and all.
Further Government of Ontario climate data is available in the rubber-chicken graph below, because data does not matter to those who do not believe in evidence based policy, science, statistics, or informed decision making.
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| Government of Ontario climate data. Oh my, it is getting big and scary just like the infographic and cbcnews.ca foretold! |