Flood gullies at Mount Chester in Bow River basin (C Loewen @Loewen_Ecology)
The southern Canadian Rockies were battered by a large flood in the summer of 2013. High waters surged across much of southern Alberta and parts of south-eastern British Columbia, causing multiple fatalities and billions of dollars of damages. The event was the most costly natural disaster in Canadian history and generated serious concern over whether flood patterns might be changing with climate.
Peak flows in Canada’s mountain streams typically occur in late spring or early summer as they swell gradually with meltwater from snow accumulated over the winter. However, the snow cover was late to melt in 2013 – fed by major snowstorms in May – and as warm, wet conditions settled over southern Alberta, they brought heavy rainfall to an unseasonably large snowpack from June 19–22. This rain-on-snow event accelerated snowmelt at high elevations, creating a ‘perfect storm’ as runoff from the melting snow intensified flooding from the unrelenting rains.
Although similar magnitude floods have occurred in Alberta’s past, it is unclear how climate or land cover variations, such as those associated with differing fire regimes, may contribute to the severity and frequency of flooding. To better understand these potential connections and how mountain floodwaters might be changing over time, researchers from the University of Saskatchewan and Environment and Climate Change Canada compared climate and wildfire data with historical streamflow measurements collected at the Bow River hydrometric station at Banff, Alberta. Looking at all available records, it appeared that flood magnitudes and volumes were decreasing since the early 1900’s; however, no significant trends were found when rain-on-snow events were analyzed separately from the more common snowmelt floods. Researchers also failed to find any clear associations between local flood characteristics and climate or wildfire. These results suggest that the Upper Bow River has been tremendously resistant to change over the past century, but also highlight the potential severity of large rain-on-snow events. Although sustained heavy rainfalls over deep snowpacks are relatively rare in the Canadian Rockies, it remains to be seen how precipitation patterns may shift with future climate change.
This is a summary article authored by Charlie Loewen. For further information, please see the original published research:
Paul H. Whitfield and John W. Pomeroy (2016) Changes to flood peaks of a mountain river: Implications for analysis of the 2013 flood in the Upper Bow River, Canada. Hydrological Processes, DOI: 10.1002/hyp.10957 (doi:10.1002/hyp.10957).
John W. Pomeroy, Ronald E. Stewart and Paul H. Whitfield (2016) The 2013 flood event in the South Saskatchewan and Elk River basins: Causes, assessment and damages. Canadian Water Resources Journal, 41:105–117 (doi:10.1080/07011784.2015.1089190).