Wind hazard in the alpine zone: a case study in Alberta, Canada

Hugenholtz, Chris H. ; VanVeller, Geoffrey S.

Année de publication
2016
Résumé
Strong winds can be a dominant characteristic of the climate in the alpine biogeographic zone and can reach speeds capable of causing people to lose balance or even blowing them over. However, in contrast to urban settings, where a considerable body of literature has examined mechanical effects of wind on people, in alpine zones the hazard associated with wind is almost entirely based on anecdotal evidence and remains largely unquantified. In this article we use archival weather station data to determine the wind hazard in the alpine zone above treeline (2543m amsl) along a popular hiking trail in the Kananaskis region of Alberta, Canada. Drawing on pedestrian wind research, we define hazardous wind at this location as any recorded wind speed >22.5ms−1. We assess wind hazard based on hourly wind speed and daily maximum gust speed for the periods 2000–2013 and 2008–2013, respectively. Results indicate that hazardous winds are almost always southwesterly, consistent with the prevailing wind, and can occur at any time of the year, but are most common in autumn and winter. Daily maximum gusts >22.5ms−1 occurred every other day on average, while hourly wind speed >22.5ms−1 occurred for 1.3–6.4% of the year. Also noteworthy is that category 1 and 2 hurricane-level wind speeds (33–42 and 43–49ms−1, respectively) were recorded at this site. The peak of category 1 wind speeds occurred in 2011 (103h in total or 1.2% of the year), while the peak in category 2 wind speeds occurred in 2009 (10h total or 0.1% of the year). A review of synoptic conditions during strong wind events suggests they are likely driven by downslope winds associated with mountain wave amplification and lee cyclogenesis. Overall, this study serves as an example to demonstrate that wind hazard in the alpine zone can be considerable and should be assessed in greater detail at all locations where people are likely to encounter strong winds.

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