Has it become warmer in Alberta? Mapping temperature changes for the period 1950–2010 across Alberta, Canada

• Published in: The Canadian geographer 2018-06, Vol.62 (2), p.144-162
• Main Author: Kienzle, Stefan W.
• Format: Article
• Language: English
• Subjects: Alberta; analyse des changements; Augmentation; Cartography; change analysis; Climate; climate index; conditions météorologiques exceptionnelles; Confidence intervals; extreme weather; global warming; Growing season; Heating; indice climatique; Mapping; réchauffement climatique; Spatial discrimination; Spatial resolution; Temperature; Temperature effects; Time series; Trends; Winter
• ISSN: 0008-3658; 1541-0064
• DOI: 10.1111/cag.12432

Key Messages Between 1950 and 2010, winter temperatures in Alberta rose by 3.5°C to 5°C in the south and up to 7°C in the north, while summer temperatures increased by less than 1°C in most of the province. The number of days with minimum temperatures below −20°C has generally about halved across Alberta, while the number of heat waves has roughly doubled. Highest confidence levels were evident for rising trends in mean annual and winter temperatures, and declining trends in the number of days below −20°C and heating degree days. When a Canada‐wide daily climate time series, covering the period 1950–2010, became available, an opportunity arose to analyze the time series for trends of a variety of temperature indices. The 6,833 climate grid cells covering Alberta, each with an area of 10 km by 10 km, allowed the detailed mapping of 30 temperature indices across the province. From each time series, an annual series was computed, which then enabled trend analyses using the non‐parametric Mann‐Kendall and Sen Slope tests. New maps could be created at an unprecedented spatial resolution, and an associated website was developed to access all trends and changes between 1950 and 2010 for all grid cells at albertaclimaterecords.com. The confidence levels of some temperature trends exceed 99%, while others are below 80%. In Alberta's south, annual average temperatures have increased by 1°C to 2°C since the 1950s, but in Alberta's north the increase is 2°C to 4°C. The growing season has lengthened by between one and five weeks since the 1950s, while the number of frost days has declined. The most significant trends observed were increases in mean annual and winter temperatures, and declines in the number of days below −20°C and heating degree days. La température a‐t‐elle augmenté en Alberta? La cartographie des changements de température pour la période 1950‐2010 en Alberta, au Canada Lorsque des séries chronologiques du climat quotidien à l’échelle du Canada couvrant la période 1950–2010 sont devenues disponibles, une occasion s'est présentée d'analyser les séries chronologiques pour les tendances d'une variété d'indices de température. Les 6 833 cellules du réseau climatique couvrant l'Alberta, chacune d'une superficie de 10 kilomètres carrés, ont permis d'effectuer la cartographie détaillée de 30 indices de température à l’échelle de la province. À partir de chacune des séries chronologiques, on a calculé des séries annuelles qui ont ensuite permis d'effectuer un