Why Flood Damages Are Increasing in Urban Areas in Canada

The important factors that explain why urban flood damages are increasing in Canada.
The only houses that flood directly because of Rain do not have a roof - not many.  Floods occurs because of the Flow of Runoff, not Rain.

Rain intensities are not increasing in Canada, on average, or to any statistically significant degree, in relation to urban flooding (short duration intensities, as opposed to number of days with rain through the year).

Rain turns into Runoff and is influenced by land use development patterns and any mitigation measures that control runoff (stormwater management).  Hydrology ([hahy-drol-uh-jee]) is the study of the rain-runoff transformations.  Stormwater management is a specialized field of Civil Engineering.  Runoff is increasing in urban areas through intensification.

Runoff turns into Flow as it is collected and concentrated in urban infrastructure, or conveyance systems (sewers, overland flow routes).  As Runoff has increased, so has flow, sometimes despite earlier mitigation efforts.

When Flow exceeds the conveyance systems capacity (Rain is above the designed level of service, or Flow capacity is reduced), collected Runoff backs-up, surcharges or spills into homes, causing Floods.  Sometimes, modifications to the conveyance system for environmental protection (prevent sewage splils) reduce capacity and contribute to Floods.

Interested in reading more detail?

Rain storm intensity not increasing shows how junk reporting has metastasized through media, economic reports and policy statements, ignoring and misrepresenting Environment Canada data

Rain - cbc news reports bogus insurance industry claim on increasing storm frequency shows that no fact checking occurs when reporting even the most outrageous claims on insurance flood damages (i.e, that there are 20 times more storms now)

Runoff and Flow - Go Train flooding not new per 1981 provincial inquiry highlights incorrect explanation of recent rail flood damages by climate change, as explained decades ago to Premier Davis using science and engineering principles like runoff hydrology (Don Watershed development) and flow hydraulics (Keating Channel dredging)

Flow -  Toronto overland flow factors affect flood risk includes recommendations on urban flood hazard management, backed up by informative new overland flood risk mapping.  Given this exposed correlation of historical basement flooding incidents and overland flow risks, you would be right to question whether insurance companies have indirectly, inadvertently insured overland flood risk in conventional sewer back-up policies. Flow is a continuum from flood plains to floor drains, whether property insurance policies try to make a distinction or not.

 And Connecting dots on climate change shows how infographics and anecdotes have replaced data and statistics in the myopic explanation of flooding that points to climate change, and ignores factors in the rainfall-runoff process (watershed development, stormwater management), and runoff conveyance (infrastructure design and operation) and ignores Environment Canada rain data.