The frequency of extreme rainfall intensities over different durations is an important engineering climatological measure used by the engineering and construction industries in planning and designing drainage structures.
Such data are also important for estimating the extent and rarity of extreme rainfall events. Environment and Climate Change Canada (ECCC) provides official Intensity-Duration-Frequency(IDF) information for Canada based on precipitation data from weather stations across Canada. These data are made publicly available by ECCC .
ECCC Extreme Rainfall Analyses
Short duration (5 minutes to 24 hours) IDF data are available for 51 locations in the Atlantic Provinces (565 sites cover all of Canada). Annual maximum rainfall (the largest rainfall event for a given duration in each year)is
identified at each location after undergoing rigorous quality control. At least 10 years of data are required for analysis. The resulting Annual maximum rainfall
series are fitted to the Gumbel Extreme Value distribution to compute the return period values. The return period is an estimate of how frequently an extreme rainfall
event can be expected at a location. A comprehensive national update to the ECCC IDF data was completed in 2014.
Extreme Rainfall Trends
Existing IDF rainfall climatologies assume that the probability extreme rainfall does not change through time. Therefore it is
assumed that older analyses and data reflect future conditions. Recent analyses show that this is not the case in Atlantic Canada and adjacent areas of the
United States. An Environment and Climate Change Canada research paper
indicates that in coastal areas of eastern Canada 1-hour and 2-hour duration rainfall extremes have shown significant increases. For shorter 5- and 15-minute durations, both increasing and decreasing trends have occurred.
