Long Term Climate Change - Short Term Extreme Rainfall Impacts - What Muzzled Scientists Can't Say


Previous posts have summarized trends in extreme rainfall for 565 climate stations across Canada. Its clear that while temperatures are up (global warming), climate change impacts are not affecting storm intensity.

Tables and maps have shown the trend direction (increasing or decreasing) and the strength of the trend (statistical significance). The complete list includes "out of service" stations and those with short periods of record, meaning their data are not as relevant to recent climate change trends. 
To focus on recent trends and more reliable long term records, the table below screens Environment Canada's stations to show only those with more than 45 years of record, and those whose last record is more recent than 2005. Only 26 stations meet this quality screening for long term, recent data sets.

Findings:

Short term extreme weather trends in western Canada show no statistically significant increase or decrease, meaning trends are minor / mild. Increases (shown as light red shading) are more prevalent than decreases (light green shading). Decreases have been observed over short durations (e.g., Calgary 5 and 10 minutes) and longer durations (e.g., Vancouver 6, 12 and 24 hour periods).

In Ontario, decreases in rainfall intensity are slightly more prevalent than increases. Statistically significant decreasing trends in rainfall extremes were observed in southern Ontario at two stations: Windsor Airport and Toronto City (aka 'Bloor Street'), shown with dark green shading. These decreases were for 7 statistics covering both short and long durations (10 minutes to 24 hours). Statistically significant increases were observed in eastern and northern Ontario for two statistics: Thunder Bay 30 minute duration, and Ottawa Airport 24 hour duration.
In the Maritimes and Newfoundland, increases are more prevalent than decreases. Statistically significant increases were observed in Moncton, New Brunswick, Shearwater Nova Scotia, and Gander, Newfoundland.

Climate Station
Province / Region		 Station ID
Engineering Climate Datasets
Annual Maximum Rainfall
Trend and Significance
Length
of
Record (Years)
Most

Recent

Year
5 min 10 min  15 min 30 min
1
hr
2
hr
6
hr
 12 hr 24 hr
British Columbia
Victoria Intl A BC        1018621 4 4 4 4 4 4 4 4 4 46 2013
Mission West Abbey BC        1105192 4 4 4 2 2 2 4 4 4 48 2010
Vancouver Intl A BC        1108395 4 4 4 4 4 4 2 2 2 59 2013


Alberta
Edmonton Int'L A AB        3012205 4 2 2 2 4 4 2 2 4 46 2011
Red Deer A AB        3025480 4 4 4 4 4 4 4 4 4 47 2012
Calgary Int'L A AB        3031093 2 2 4 4 4 4 4 4 4 56 2009


Saskatchewan
Estevan A SK        4012400 4 4 4 4 4 2 4 2 4 48 2011
Kindersley A SK        4043900 4 4 4 4 4 4 4 4 4 47 2013


Ontario
Ear Falls (Aut) ON        6012199 4 4 4 4 2 2 4 4 4 49 2006
Geraldton A ON        6042716 4 4 4 4 4 4 4 4 4 48 2006
Thunder Bay Cs ON        6048268 4 4 4 5 4 4 4 4 4 47 2006
Timmins Victor Power A ON        6078285 4 4 4 4 4 4 2 2 2 47 2006
Kingston Pumping Station ON        6104175 4 4 2 2 2 2 2 2 2 63 2007
Ottawa Cda Rcs ON        6105978 2 2 2 2 2 2 4 4 5 50 2007
St Thomas Wpcp ON        6137362 4 2 2 2 4 2 4 4 4 75 2007
Windsor A ON        6139525 2 1 2 2 2 1 1 1 2 60 2007
London Cs ON        6144478 4 4 4 4 2 2 2 2 2 57 2007
Toronto City ON        6158355 2 2 2 2 2 2 1 1 1 59 2007
Toronto Intl A ON        6158731 2 4 4 4 4 4 2 2 2 60 2013


Maritimes / Newfoundland
Charlo Auto NB        8100885 4 4 4 4 4 4 4 4 4 51 2013
Moncton Intl A NB        8103201 4 4 4 4 4 4 4 5 5 64 2013
Sable Island NS        8204700 4 4 4 4 4 4 4 4 2 50 2012
Shearwater Auto NS        8205091 4 4 4 5 4 4 4 4 4 53 2009
Sydney Cs NS        8205702 4 4 4 4 4 4 4 2 4 50 2013
Gander Airport Cs NL        8401705 4 2 2 4 4 4 5 5 5 65 2009
Goose A NL        8501900 4 4 4 4 4 4 4 2 2 50 2013

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Sensitivity analysis on the screening criteria do not change the overall trends. We looked at period of record greater than 38 years, instead of 45 years, and this doubled the number of stations. Highlights:
  • The Ottawa International Airport station was added and had a statistically significant decrease in short term rainfall intensity (10 minutes, 15 minutes, 1 hour) - this is consistent with Ottawa CDA which had decreasing non-significant trends for 5 minute to 2 hour durations.
  • In the northern Ontario, Sault St. Marie Airport was added with a statistically significant increase over a one hour duration, just like Thunder Bay.
  • Statistically significant increases in rainfall over long durations (12-24 hours) were added in British Columbia (Tofino Airport, Blue River Airport).
  • A statistically significant increase was added at Fredericton CDA (5 minute duration).
Environment Canada's recent article on extreme rain trends published in Atmosphere-Ocean confirms there are no overall trends in rain intensity, and there are some regional minor increases and decreases - click for abstract.

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