Hazardous weather events in the St Lawrence Valley from the French regime to Confederation: descriptive weather in historical records from Quebec City and Montreal, 1742–1869 and 1953—present

Daily weather records for the St Lawrence Valley region in Québec, Canada, exist on a continuous basis for nearly two centuries and on a more fragmentary level back to the French regime. Daily and sub-daily observations allow for the potential to reconstruct and analyse not only hazardous weather events of short duration but also high impact events such as freezing rain, snowstorms, blowing snow or thunder. Weather records can also give us a more detailed understanding of longer lasting events, such as consecutive dry days leading to drought, or long winters with consecutive frost days which have an impact on health and the demand for domestic heat, which can itself lead to hazardous conditions for air quality. Dry summers, severe snowstorms and long winters have always occurred in the St Lawrence Valley region. This paper looks at the frequency and evolution of a subset of weather events which constitute natural hazards over a period of centuries, from 1742 to the present day, with gaps from 1754–1798 and 1870–1953. The annual frequencies of most events fall broadly within the same ranges over the course of the past centuries. However, a decrease in the number of consecutive dry days and a concomitant increase in precipitation-related hazardous events, such as thunder and freezing rain, can be seen in the twentieth and early twenty-first centuries compared to the nineteenth century. The mid-eighteenth century also saw a high frequency of freezing rain events. A mid-twentieth century peak in the number of days with smoke also stands out and is related to industrial and domestic sources of heating and energy.