Except that these so called 100-year event are happening more and more often - and the trend with increasing temperature is upward. Like today we are dealing with basically all highways in the core and all heavy transit getting interrupted - that’s unacceptable.
AoD
This is correct. The generally accepted standard in Toronto has been that the DVP should be flooded ideally no more than once in 25 years; though in practice once in 5 was tolerable.
We're now closing in on once every 2 years, at least briefly..........
*****
This is not just something to blame on climate change, though that may have a role; its sprawl and increased hardscape. Remember my arguments against paving over backyards and cutting down tree canopy; this (in part) is the result.
So is greater density (greater base flow in the sewer means it overflows sooner).
So its a combination of more intense rainfall over a shorter period, combined with fuller sewers, and less natural storage/infiltration for water.
This is why we need to be careful about cutting down mature trees and replacing homes w/lawns w/buildings that occupy more lot area.
That doesn't mean you can't build better, somewhat denser, and w/less paved area.........that you can do......but its a thoughtful, nuanced exercise in which some of the land you recover by building taller you devote to more parkspace.
Its not an argument for SFH-based sprawl, nor against towers, its an understanding of math.....volume of water, stored, and displaced. Hard surfaces cause problems, for which mitigation can be extremely expensive.
And if you don't do green roofs that fully offset permeable space loss........you need even more............but of course doing fully green roofs is expensive and means things like mid-building mechanicals.....which in turn makes housing less affordable, its all rather nuanced and complicated which is why I have an allergy to simplistic arguments from any perspective.
. Here are the pics: