This blog has reviewed annual maximum rainfall series trends in the past, including all the v2.30 Engineering Climate Dataset trends across Canada. Also v3.00 trends for stations with long term records and southern Ontario derived IDF trends for long-term stations.
Overall most trends are not statistically significant and the few percentage of significant increases and decreases can be explained largely by chance. The follow charts compare the trends for all Environment and Climate Change Canada's Canadian stations using the v2.30 data and the newest v3.00 data release in winter 2019.
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| Maximum rainfall trends in Canada. Environment and Climate Change Canada's Engineering Climate Datasets. |
What do the charts show? Not much change after adding 15% more stations and up to 10 years more data. The following tables illustrate the percentages of significant ups and downs (red and green bars), non-significant changes (the grey bars) and no data (not shown in the charts).
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| Maximum rainfall trends in Canada - Direction and Statistical Significance. Environment and Climate Change Canada's Engineering Climate Datasets v2.30 and v3.00 Comparison. |
The data show that in v2.30 over 86% of trends were not significant. In v3.00 a bit fewer statistics were non-significant. The increase in statistically significantly trends was 0.09%. The increase insignificantly significant decreases was 0.03%. These are essentially zero changes.
Nationally, there are more significant increases than decreases. Some regions, however have trends that go against these averages. In southern Ontario, there are a few more decreases than increases, but twice as many statistically significant decreases than increases:
Decreasing annual maximum rainfall volumes over all durations 5 minutes - 24 hours = 43.4%
Zero trend in annual maximum rainfall volumes over all durations 5 minutes - 24 hours = 4.3%
Increasing annual maximum rainfall volumes over all durations 5 minutes - 24 hours = 42.1%
Number of statistically significant decreases = 12
Number of statistically significant increases = 6
