|Toronto: temperature up - rainfall down|
The tables at right show intensities for "Toronto City" Climate Station ID 6158355 (aka "Toronto" 6158350) for three recent Environment Canada IDF curve updates:
- Up to 1990 (47 years of record)
- Up to 2003 (57 years of record)
- Up to 2007 (61 years of record)
Design rainfall intensities are shown for short durations of 5 minutes, 15 minutes and 1 hour in the three tables.
- Up to 1990 (38 years of record)
- Up to 2003 (51 years of record)
- Up to 2007 (54 years of record)
- Up to 2013 (60 years of record)
What do the Toronto and Mississauga "Toronto Pearson" IDF trends mean for drainage design? Hopefully nothing. Although downtown Toronto trends have been steadily decreasing, the most recent 2013 storm is not included and could moderate the downward trend in severe rainfall statistics. Although Mississauga Pearson has some increasing intensities, this is skewed by the timing of the most recent record and absence of even more recent below average data points. And although some Mississauga intensities increase (above 5 year, 1 hour data), short duration values remain below downtown Toronto values in an absolute sense, meaning the Mississauga values are just 'catching up' to the historically higher Toronto ones. To illustrate this, up to 1990 the 5 minute Toronto 100 year design intensity was 21% above the corresponding Pearson value. In 2007, that Toronto statistic was still 20% higher.