BC Earthquake and Flood Hazard Zones - Natural Hazard Locations Key To Risk Management

BC Earthquake
BC Earthquake Risk Map
BC Earthquake
BC Earthquake December 2015 in High
Shake Hazard Zone
Location , location , location.

Was the December 30, 2015 earthquake in BC unexpected? No. It occurred in a high shake hazard zone as shown in the image to the left. Certainly risks can be managed when hazards are better known and policies are put in place to manage them.

Flood risks are like earthquake risks, as they are based on location.  For river flooding, floodplain maps show hazards due to high river flood levels.  This post shows the hazard zones maps available in BC.

Urban overland flood hazards can be predicted as well, beyond
regulated valley limits with river flood plain hazard zones.
We cannot predict where the next major storm will occur but the physical characteristics of the your location will put you in a hazard zone when and if that storm comes.

Calgary flooding was in a river flood hazard zone, known to be high risk, but ignored in terms of land use planning and flood plain regulation. Other urban flooding hazard locations have been thought to be difficult to map and manage, but research by CityFloodMap.Com shows those locations, beyond tranditional river valley flood plains, can be mapped as well - see image to right and our previous post on the details of analysis of Toronto flood events. Urban overland flood paths are like earthquake fault lines - you can't see them most of the time as they are usually inactive. And they both have wide areas of influence beside them - for overland flood paths this influence is because properties in the flow path are connected to many others by an underground sewer network - for fault lines the earth is connected.

Sometimes media get confused about location and assign risk from one area to another by mistake. In Toronto, when the GO Train was stranded in the Don River flood plain, the media, the train operator and the Environmental Commissioner of Ontario explained it as an unprecedented weather event, some linking it to climate change. How wrong.

Natural hazard reporting needs better
science in reporting causes.
In fact the record rainfall on July 8, 2013 that stranded the GO Transit commuter train was in Mississauga, in the Etobicoke Creek Watershed, several watersheds away from the Don River`s watershed. Rainfall in the East York area on the Don River Watershed recorded only 51 mm of rainfall according to the closest Environment Canada gauge - much less than the record 126 mm of rainfall in Mississauga`s Pearson International Airport.  The rail line was also in a high risk flood zone, not unlike "High River" Alberta was (and is).

More details on GO Train flooding are in a previous post. The following illustration shows how basic physical facts, including location, are ignored when reporting on the location of natural hazards and incidents:
BC Earthquake
Reporting on natural hazards should focus on basic facts, unlike the Toronto GO Train flood reporting that linked the stranded commuter train to record rainfall in a different watershed beyond the flooded Don River flood plain.
Location, location, location is important for assessing natural hazards and interpreting extreme rainfall.
Often media reports will not identify the spatial variability extreme rainfall, and may only have access to information available through Environment Canada which has a few active rain gauges (climate stations) that record short duration rainfall intensities.  The image above shows scattered Environment Canada stations. Below, more detailed City of Toronto data is explored.

Toronto Water, the group responsible for Environmental Assessment Studies that investigate flood causes and recommend solutions, summarized rainfall patterns for a Ward 11 community meeting on July 19, 2013 shortly after the July storm - recorded rainfall data is available from locations than Environment Canada sites. The presentation to the community showed very little to moderate rain recorded in the eastern part of Toronto, and few reported basement floods. The Don Watershed limits have been added to the a community meeting slide to show that only moderate rainfall was observed overall in the Don River Watershed.

Moderate rainfall in the Don River Watershed corresponds to an overall 5-10 year return period design event, with some Toronto gauges recording less than 2 year return period rainfall (19 mm) in the eastern part of the Don River Watershed, and some gauges on the western edge recording higher total.

As a result of the variable rainfall pattern The Toronto Observer reported that according to the Insurance Bureau of Canada, the Scarborough community was 'unscathed' by the July 8, 2013 event. This is supported by comments provided by Toronto Water in the report:

July 8, 2013 Storm Variability Toronto
Toronto Water received over 4,700 calls regarding basement flooding, but only 50 came in from Scarborough, said Ted Bowering, director of water infrastructure management for Toronto Water.

In Scarborough in fact the storm wasn’t all that intense. It was kind of like a normal summer thunderstorm,” he said. “So the impact was not that great at all.”

Flood reports vary after July 8, 2013 storm in Toronto. Less than 2% of
reported floods were from East Toronto (Scarborough). 
A City of Toronto staff report provides a less cluttered summary map of the rainfall variability and a summary table of reported flooding. The table shows less than 2% of reported flooding was in eastern Toronto, demonstrating the variability in rainfall severity.

Location can be miscommunicated even by the best managers. For example the TRCA summarized extreme rainfall events in Ontario and implied Mississauga rainfall was in Toronto and did not distinguish between watersheds where rainfall occurs and where it causes flooding:
Go Train flood toronto
Mississauga's CN Tower? Location matters in hydrology. Extreme rainfall is not evenly distributed and can be high in one watershed and low in another. This was the case for Hurricane Hazel and also the July 8, 2013 storm - both storm were light on east Toronto (including the Don River Watershed) and heavy in the western watersheds including those outside of Toronto.
Note: August 19, 2005 storm appears mislabeled as '2013'.

So location matters for natural hazard risks. Extreme rainfall is highly variable in terms of its spatial pattern. Sometimes local data, beyond that which is available from Environment Canada, can be used to assess the variability in rainfall across watersheds and drainage catchments,


To help assess flood risks, CityFloodMap.Com has created Canada-wide mapping of extreme rainfall trends so that risks of flooding due to higher rainfall can be assessed for 565 climate stations locations. Fortunately, this Environment Canada data shows that only a few percentage of the stations have a statistically significant increase in observed extreme rainfall. CityFloodMap.Com has also created tablular summaries of extreme rainfall trends, summarized by province.