There is an increased frequency with flood events.
Extreme weather events have always occurred. This is nothing unusual. What is unusual is how frequently they now occur. These occurrences have been formally studied and there is significant evidence to back up this claim. For example, in the last five years, Southern Alberta has seen, not only flooding, but an increase in the severity of the flooding and a change in the timing of flooding (that is, earlier in the season than usual) (Cole, 2018). This flooding is due to a few different causes (Sutherland, 2016):
- a large amount of precipitation falling at once;
- melting snowpack; local rivers breaching their banks;
- warmer than seasonal temperatures;
- the inability of soils to absorb the water; and
- the geography of the area (at the base of a slight downward slope from the foothills)
The earth’s changing temperature is likely one of the main causes of this flooding phenomenon (Hirabayashi et al., 2013). And, according to Milly et al. (2002), the frequency of great floods around the world have increased substantially during the 20th century—and this trend, according to climate models, is expected to continue.
Much of Southern Alberta is in flood plain and downslope from the Rocky Mountains, so that region is naturally at risk with warmer spring temperatures that melt the mountain snow quickly. Add to that the excessive precipitation and a frozen or saturated ground, there is nowhere for extra water to go, causing flooding.
Because of Southern Alberta’s geography and hydrology, they are not strangers to flooding. In the past 150 years, there have been some major floods, but the last one was before 1932, then a very long ‘dry’ stretch, and then about five major floods in the last 23 years (The Weather Network, 2013). It is more likely than not that these great floods will occur again in the 21st century. In fact, there’s almost a 30 per cent chance it will happen again by 2050 (The Weather Network, 2013).
References
Cole, Y. (March 27, 2018). Rapid spring melt puts Taber region on flood alert. Retrieved from http://calgaryherald.com/news/local-news/state-of-emergency-continues-in-taber-region-as-concerns-about-overland-flooding-grow
Hirabayashi, Y., Mahendran, R., Koirala, S., Konoshima, L., Yamazaki, D., Watanabe, S., …Kanae, S. (2013). Global flood risk under climate change. Nature Climate Change, 3(9), 816-821. doi:10.1038/nclimate1911
Milly, P., Wetherald, R., Dunne, K., & Delworth, T. (2002). Increasing risk of great floods in a changing climate. Nature, 415(6871), 514-517. doi:10.1038/415514a
Santa Maria, C. (June 17, 2014). Flood warnings issued in southern Alberta. Retrieved from https://www.theweathernetwork.com/news/articles/flood-warnings-issued-in-southern-alberta/29729/
Sutherland, S. (June 21, 2016). Three years later: What caused the 2013 Alberta floods? Retrieved from https://www.theweathernetwork.com/news/articles/why-was-southern-alberta-so-vulnerable-to-flooding-in-2013/29800/
The Weather Network. (June 25, 3013). Calgary Floods: It could happen again. Retrieved from https://www.theweathernetwork.com/news/articles/calgary-floods-it-could-happen-again/8295/
