Research and Policy Programs to Address Canada’s Increasing Flood Risk.

The objective of this paper is to present results of a climate-impact assessment of fluvial and pluvial flood damages to residential properties in Canada. It also includes information on coastal flooding, future development, and four major policy programs currently underway to address the country's increasing flood risk. Flooding is the costliest natural hazard in Canada, with flood generating mechanisms including intense rainfall, snowmelt runoff, rain on snow events, ice-jams, coastal storms, cyclones and hurricanes, and glacial melt. Recent flood events in Canada have also been triggered by complete or partial failure of engineered flood management structures such as dams and levees. Canada's climate is warming at a rate twice the global average, with the northern regions seeing three times the rate of warming (Bush et al., 2019). Climate change is expected to increase the frequency, magnitude and intensity for all types of flooding in Canada. For this presentation, we will focus on three broad categories of flooding: pluvial (caused by extreme rainfall), fluvial (caused by river overtopping), and coastal flooding.

Public Safety Canada is Canada’s federal department responsible for emergency management, and has a mandate to keep Canadians safe from a range of risks, including natural disasters. At Public Safety, we use two general types of flood mapping: targeted, local-scale engineered flood mapping, performed by provinces and territories for regulatory purposes, and mapping generated by large scale flood modeling, often undertaken primarily to estimate risk across large areas, at multiple return periods and flood generating mechanisms. The latter is used to fill the gaps in regulatory flood mapping where detailed data for hydrologic and hydraulic modelling is unavailable. The current picture of flood mapping in Canada is that there is inconsistency between jurisdictions, and many areas are unmapped or have flood hazard maps that are out of date.

Several federal partnership programs have worked to address these gaps. The first of these initiatives was the Flood Damage Reduction Program (FDRP) spanning 1975-1996 when the Government of Canada collaborated with provincial governments to identify flood hazard areas with the aim of implementing actions aimed at reducing future flood losses (Watt, 1995). The second major initiative in Canadian flood hazard mapping began with the launch of the National Disaster Mitigation Program (NDMP) spanning 2015-2020, a $200 million initiative aimed at supporting provincial and territorial efforts to reduce flood risk, including through mapping (Public Safety Canada, 2021). Most recently, in 2021, the Flood Hazard Identification and Mapping Program (FHIMP), a $63 million (plus new funds) initiative intended to support provincial and territorial endeavors in conducting flood hazard assessments, mapping flood-prone areas, and disseminating flood hazard information to the public, was launched (Natural Resources Canada, 2022).

Public Safety Canada is conducting research to estimate current and future flood damage across Canada in support of major policy programs. A preliminary study was conducted to estimate future flood damage from fluvial and pluvial floods over 15.4 million residential properties in Canada. The study used the KatRisk flood modelling framework (https://www.katrisk.com/). In the model, a worldwide precipitation dataset is used to generate 50,000 years of stochastic precipitation events, which are routed through hydraulic and hydrological models on a local Digital Elevation Model (DEM) grid to model pluvial and fluvial floods for all catchments in Canada south of 60 degrees North. The pluvial model utilizes finite volume methods to allow water to flow over the utilized DEM, tracking flood maximums at each time step. Fluvial flooding is calculated for all catchments with one or more upstream catchments. The input flow for each catchment is determined by the output flow from the upstream catchments using canonical routing equations with lateral inflow from a hydrological model added along the river channel. With the upstream flow computed, KatRisk then allows the water to travel from the head to the mouth of the catchment using the 2-D Shallow Water equation on the above mentioned DEM data set. The future precipitation extremes are modelled as a function of future changes in temperatures following Clausius-Clapeyron relationship which increases extreme precipitation by 7% every 1℃ increase in temperatures.

The findings from our work indicate that climate change is likely to exacerbate flood damages from fluvial and pluvial flooding in Canada under all climate scenarios. Increases in coastal flood damages, and damages due to increased development, are also expected. This presentation will focus on the results on this analysis, and the major public policy programs underway in Canada to address Canada’s rising flood risk.

References

Bush, E. and Lemmon, D.S., editors (2019): Canada’s Changing Climate Report; Government of Canada, Ottawa, ON. 444 p.

Natural Resources Canada (2022) Flood Hazard Identification and Mapping Program. https://www.nrcan.gc.ca/scienceand-data/science-and-research/natural-hazards/flood-hazard-identification-and-mapping-program/24044

Public Safety Canada (2021) National Disaster Mitigation Program. https://www.publicsafety.gc.ca/cnt/mrgncmngmnt/dsstr-prvntn-mtgtn/ndmp/index-en.aspx.

Watt, W. E. (1995) The National Flood Damage Reduction Program: 1976-1995. Canadian Water Resources Journal, 20(4), 260 237–247.