Annual Maximum Rainfall Trends in Canada - Environment and Climate Change Canada's Updated V3.20 Datasets Show Few Significant Trends

Previous posts have presented overall trends in annual maximum observed rainfall amounts at Canadian climate stations (link: https://www.cityfloodmap.com/2020/12/design-rainfall-trends-in-canada.html).

Environment and Climate Change Canada (ECCC) periodically updates trend analysis on the annual maximum series (AMS) for each station, and these series are used to derive design intensities, i.e., Intensity-Duration-Frequency curves. Data area available here (link):  https://climate.weather.gc.ca/prods_servs/engineering_e.html

In May 2021 additional analysis has been included in these Engineering Climate Datasets. The "Whats_New_EC_IDF_v3-20.pdf" file includes a summary table that provides counts of stations and additional station years added with recent update:

The v-3.20 update adds 490 station-years of data. There are currently 17,133 station-years of data. The average length of record is 25.3 years. This represents a slight decrease in record length compared to 25.5 years in v-3.10, as new short record stations are factored in.

Trends in annual maximum rainfall have not change all relative to the 2020 v-3.10 data. The majority of station data show no statistically significant trend. The table below compares trends in earlier datasets, averaged across all durations. 

Trend in Maximum Rain    v3.20       v3.10       v3.00         v2.30

Significant Increase              4.16%     4.28%       4.18%        4.09%

Significant Decrease             2.25%     2.24%       2.33%        2.30%

No Significant Trend          85.73%    85.80%     85.55%      86.37%

No Calculation                      7.86%      7.68%       7.94%        7.24%

 

The v-3.20 datasets  have the following trends within various durations:


Excluding 'No Calculation" data, annual maximum observations with 'No Significant Trend' represents 92-94% of series, with an average of 93.0%. Excluding the 'No Calc' data results in an average of 4.5% significant increases and 2.5% significant decreases.

The following chart shows that majority of station data show no statistically significant trend.



There has not been any appreciable change in the annual maximum rainfall trends considering earlier datasets (see v-2.30 to v-3.00 update https://www.cityfloodmap.com/2020/02/annual-maximum-rainfall-trends-in.html)

In Canada, the number of stations with annual series used to derive extreme rainfall statistics continues to increase. A previous post explored how manually-operated climate stations have been declining while this increase occurs (link: https://www.cityfloodmap.com/2020/06/do-we-have-enough-climate-stations-in.html). In 1990 there were only 11,268 station-years of data. Today with 17,133 station-years of data we have 52% more information to guide assessments of extreme rainfall.  

This table summarizes the rise in climate station count and rise in station-years as new data is added.


Some have confused the decline in manual stations with a decline in overall data (see the above post). This chart shows the rise in climate stations with IDF data used for engineering design (orange lines), along with the decline in manual station data (blue bars).







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