Evolution of Winter Temperature in Toronto, Ontario, Canada: A Case Study of Winters 2013/14 and 2014/15


Globally, 2014 and 2015 were the two warmest years on record. At odds with these global records, eastern Canada experienced pronounced annual cold anomalies in both 2014 and 2015, especially during the 201314 and 201415 winters. This study sought to contextualize these cold winters within a larger climate context in Toronto, Ontario, Canada. Toronto winter temperature ($T{max}$, $T{min}$, and $T{mean}$) for the 201314 and 201415 seasons were ranked among all winters for three periods: 184041 to 2015 (175 winters), 195556 to 2015 (60 winters), and 198586 to 2015 (30 winters), and the average warming trend for each temperature metric during these three periods was analyzed using the Mann‒Kendall test and Thiel‒Sen slope estimation. Winter 201314 and 201415 were the 34th and 36th coldest winters in Toronto since record-keeping began in 1840, however these events are much rarer, relatively, over shorter periods of history. Overall, Toronto winter temperatures have warmed considerably since winter 184041. The Mann‒Kendall analysis showed statistically significant monotonic trends in winter $T{max}$, $T{min}$, and $T{mean}$ over the last 175 years, and 60 years. These trends notwithstanding, there has been no clear signal in Toronto winter temperature since 1985‒86. However, there was a statistically significant increase in the diurnal temperature range in that period, indicating an expansion of winter extremes. We propose that the possible saturation of urban heat island-related warming in Toronto may partially explain this increase in variation. We also identify anomalies in the position of the polar jetstream over Toronto during these cold events. We find no direct influence of major teleconnections on Toronto winter temperature.

Journal of Climate