Spatial and temporal characteristics of extreme temperatures over Canada

The detection and attribution of past trends, changes, and variability in climate variables (including extremes) is essential toward the understanding of potential future changes resulting from anthropogenic activities. This is especially true for high latitude regions such as Canada where climate change signals are anticipated to be stronger. The current investigation examines extreme temperature trends and variability over Canada during the 20th century. Using a recently created, rehabilitated daily temperature data set (consisting of 210 relatively evenly spaced stations across the country), both the spatial and temporal characteristics of selected extreme temperature indices are presented. Results show that over a large portion of the country, there have been increasing trends in extreme low daily temperature values. These occur on both annual and seasonal time scales with winter and especially, spring showing the largest trends. Responses tend to be strongest over western and central Canada, but opposite over the northeast. Analyses of extreme high daily temperature values also indicate increasing trends, however, they are generally not as pronounced as the minimum extremes. In fact, summer is associated with small, insignificant trends over the majority of the country. Extreme maximum results are spatially similar to those of minimum temperature with positive trends over western and central Canada, and negative trends over the northeast. The extreme temperature findings comply with observed trends in average Canadian temperature which show largest warming over the west, highest rates during winter and spring, and minimum temperatures increasing more than maximum. The significant decrease in extreme temperature values over north-eastern Canada is also consistent with the significant cooling trend observed over this area during the last half century. Trends and variability in other extreme temperature related indices including various daily maximum and minimum temperature threshold exceedences (e.g. 5th and 95th percentiles), hot/cold spells, and annual maximum and minimum extreme temperature return periods are also presented.