|BC Earthquake Risk Map|
|BC Earthquake December 2015 in High|
Shake Hazard Zone
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.
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.
|Natural hazard reporting needs better|
science in reporting causes.
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.
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|
“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).
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:
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.