Impact of Climate Change on the Number of Frost-free Winter Days in Prairies and Eastern Provinces of Canada

Abstract

Highlights In northern region of Prairies and eastern provinces of Canada, the change in Frost-Free Days (FFDs) for the period of 1938–2022 is nearly negligible. In the stations located at the south of Ontario (called southern stations here), a maximum increase of 4.4 to 5.8 in FFDs per month was noted during the study period at different locations. The rates of change in FFDs per unit °C of the monthly mean of the daily minimum temperature (MMDMT) vary from a minimum of 0.001 to a maximum value of 2.92 days at the selected stations. Abstract. Although a considerable number of studies related to the impact of climate change on temperature-related variables have been conducted, studies exploring the changes in indices of daily winter temperatures, such as variation in the number of frost-free days (FFDs), for the winter season or for each month of the season are very few. The main objective of this study was to explore temporal trends in FFDs for each month of the winter season as well as examine the relationship between FFDs and the monthly mean of daily minimum temperature (MMDMT) at the selected stations in the central and eastern provinces of Canada. Daily minimum temperature data between 1938 and 2022 from 11 meteorological stations situated along a wide range of latitudes across the Prairies and eastern provinces of Canada has been analyzed. An exceedance probability model is developed to predict the FFDs for each winter month. The analysis leads to the conclusion that the number of FFDs per month exhibited an exponential relationship with the MMDMT for November, April, and the entire winter season, while the relationship for December through March followed a second-order polynomial curve. The results further highlight that the rate of change in FFDs per month varies across stations for each month. Notably, while the change is minimal for stations such as Kuujjuaq, Kuujjuarapik, and The Pas, it has notably increased by 23.1, 17.9, and 14.2 days at the Toronto, Windsor, and London stations, respectively. Additionally, it was observed that the rates of change in FFDs per unit increase in MMDMT (in °C) are consistently positive for all months and selected stations. The rate of change varies, ranging from a minimum of 0.001 at The Pas in December to a maximum value of 2.92 days at Montreal in April.Moreover, coefficient of determination (R2) values of more than 0.96 were observed for both exponential and second-order polynomial relationships in the months of November and April, as well as for the entire winter. A rising trend in MMDMT values, along with a decreasing trend in the MMDMT standard deviation values, was observed across all stations from 1938 to 2022. This trend indicates a more pronounced and predictable rise in temperature over time. Overall, the number of FFDs is increasing for all winter months, albeit with a few exceptions, at central and eastern stations in Canada. These warming trends during the winter months contribute to the expansion in the number of FFDs, which is expected to significantly impact hydrological, agricultural, and environmental processes within the study region. Keywords: Climate change, Exceedance probability model, Frost-free days, Monthly mean of daily minimum temperature.