Documentary Data Rescue In Canada: Daily Temperature Records For The St-Lawrence Valley In The Past 270 Years

English Abstract:

Daily weather observations in Montreal and Québec City from the mid-1700s until the end of the 19th century have been digitized by a crowd-source citizen science data rescue project. Sub-daily (typically two or three observations per day) temperature readings from 14 different sources were assessed for quality using observational frequency techniques by comparing the historical observations with modern hourly data. A series of regression models were constructed and validated to estimate historical daily minimum and maximum temperature from the sub-daily historical measurements. The reconstructed minimum and maximum temperatures were used to compile a single series of daily minimum and maximum temperatures for the St-Lawrence Valley region between 1742 and 2010, with nearly continuous observations from 1798 to 2010. These daily temperatures were analyzed for changes and variability over the past two and half centuries. Cold conditions prevailed in the 1810s, 1830s and 1880s, while warm summers were observed in 1808, 1825, and 1955. Documentary evidence also suggests warm summers and frequent drought in the mid-18th century, with the hot and dry summer of 1754 described in particular detail. While there are warming tendencies in minimum temperatures, especially in winter with no very cold winters since the 1930s, little change over the century time scale is seen in maximum temperatures. Climatic indicators such as heat wave and cold spell counts suggest considerable decadal scale variability over the past 200 years.