Exceedance Probability Model for Predicting the Frequency of Frost-Free Days

Abstract

Highlights Number of frost-free days (FFD) increased exponentially with an increase in winter daily minimum temperatures. Winter daily minimum temperatures increased at a rate of 2°C per 100 years for the investigated stations. Stations situated in southern Canada are more susceptible to increase in winter FFD. The developed simple model can be used to reliably forecast FFD and other temperature related variables. Abstract. Data collected between 1940 and 2009 from 11 weather stations across central Canada were used to explore temporal changes in mean winter daily minimum temperatures (WDMT) and the number of frost-free days (FFD) per winter. The main objective of the study was to estimate and predict temporal trends in FFD per winter, as well as to investigate the relationship between FFD and mean (WDMT) across a wide range of latitudes in central Canada. An exceedance probability model was developed to predict FFD per winter based on the definition of FFD per winter as an exceedance variable, the normal distribution function as an approximation of the frequency distribution of WDMT, and a relationship between the standard deviations and means of WDMT. The analyses of the mean WDMT time series revealed an overall average temperature increase of about 2°C over 100 years for the investigated stations. Further, the stations in central Canada have experienced an increase in FFD, with an average increase of 12 days in 100 years. The rate of increase in FFD, however, varied considerably among the 11 stations, from approximately 0.6 to 36 days per 100 years. Stations situated at northern latitudes exhibited relatively small increases, or no increases in FFD per winter, as compared to stations situated in southern areas. The FFD per winter were found to increase exponentially with steady increases in the mean WDMT values, matching the results obtained by solution of the developed exceedance model. Therefore, the exceedance model was shown to be an excellent tool for predicting FFD per winter, at least for the stations located widely across central Canada. Keywords: Climate change, Exceedance probability model, Frost free days, Minimum daily temperature.