INTERNATIONAL JOURNAL OF CLIMATOLOGY Int. J. Climatol. (2015) Published online in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/joc.4282 Comparison of the temporal variability of winter daily extreme temperatures and precipitations in southern Quebec (Canada) using the Lombard and copula methods Nadjet Gueri, a Ali A. Assani, a * Mhamed Mesioui b and Christophe Kinnard a a Département des sciences de l’environnement et Centre de Recherche sur les Interactions Bassins Versants-Écosystèmes aquatiques (RIVE), Université du Québec à Trois-Rivières, Canada b Département des Mathématiques et d’Informatique, Université du Québec à Trois-Rivières, Canada ABSTRACT: Although numerous studies have looked at the long-term trend of the temporal variability of winter temperature and precipitation in southern Quebec, no study has focused on the shifts in series means and the dependence between these two types of climate variables associated with this long-term trend. To ill these gaps, we used the Lombard method to detect the shifts in mean values and the copula method to detect any change in dependence between extreme (maximum and minimum) temperatures and precipitation (snow and rain) over the periods 1950 – 2000 (17 stations) and 1950 – 2010 (7 stations). During these two periods, the shifts in mean values of temperature and precipitation were recorded at less than half of the stations. The only signiicant change observed at the provincial scale is a decrease in the amount of snowfall, which occurred in many cases during the 1970s. This decrease affected stations on the north shore (continental temperate climate) more strongly than stations on the south shore (maritime temperate climate) of the St Lawrence River. However, this decrease in the amount of snowfall had no impact on the dependence over time between temperature and precipitation as snow. KEY WORDS winter maximum and minimum daily temperature; winter rainfall; winter snowfall; Lombard method; copula; southern Quebec Received 28 July 2014; Revised 2 January 2015; Accepted 13 January 2015 1. Introduction In the current climate change context, an increasing amount of work focuses on the changes that affect the temporal variability of temperature and precipitation in many regions of the world. Many studies have looked at this issue in Canada in general and in Quebec in particular (e.g. Brown and Goodison, 1966; Groisman et al., 1994; Brown and Braaten, 1998; Stuart and Isaac, 1999; Zhang et al., 2000; Langlois et al., 2004; Vincent and Mékis, 2006; Yagouti et al., 2008; Turner and Gyakum, 2010; Mekis and Vincent, 2011; Zeng et al., 2011; Nalley et al., 2012; Adamowski et al., 2013; Fortin and Hétu, 2013). These studies have shown that the extent of changes in temperature and precipitation regimes is geographically and seasonally dependent. Based on an analysis of trends in temperature and precipitation from 1900 to 1998, Zhang et al. (2000) observed a generalized increase in annual mean temperature ranging 0.5 – 1.5 ∘ C in southern Canada, particularly in the western part of the country. This warm- ing, however, is greater for minimum temperatures than for maximum temperatures. At the seasonal scale, warming is * Correspondence to: A. A. Assani, Département des sciences de l’environnement et Centre de Recherche sur les Interactions Bassins Versants-Écosystèmes aquatiques (RIVE), Université du Québec à Trois-Rivières, Trois-Rivières, Canada. E-mail: Ali.Assani@uqtr.ca generalized in winter and spring, with the most extensive warming having occurred in the spring. However, data from 1950 to 1998 revealed a decrease in temperature in the northeastern part of Canada, including Quebec. As far as precipitation is concerned, Zhang et al. (2000) noted a generalized increase in total annual precipitation ranging from 5 to 35% from 1900 to 1998 in southern Canada. This increase is thought to result mainly from increased amounts of snow in fall and winter, with the snow to total precipitation ratio having increased signiicantly in many regions of the country. However, negative trends of this ratio were observed in other southern regions in winter. In southern Quebec, no signiicant change in the amount of precipitation is observed for either winter or spring. These trends in temperature and precipitation were for the most part conirmed by subsequent studies in various regions of Canada. However, the extent of temperature and precipitation increases varies from one study to the next as a result of the differences in the period over which data are analysed. For Quebec, Yagouti et al. (2008) also observed a trend of increasing temperature from 1960 to 2005, par- ticularly in the southern, western and central regions of the province. This warming trend is particularly strong in win- ter. The same authors also observed a trend of increasing annual total precipitation, as well as of low-intensity rain in winter. In contrast, total snow height decreased, a trend also observed by Brown (2010). For their part, Fortin and © 2015 Royal Meteorological Society