Observed Trends in Severe Weather Conditions Based on Humidex, Wind Chill, and Heavy Rainfall Events in Canada for 1953–2012

Abstract

Observed trends in severe weather conditions based on public alert statements issued by Environment Canada are examined for Canada. Changes in extreme heat and extreme cold events represented by various humidex and wind chill indices are analyzed for 1953-2012 at 126 climatological stations. Changes in heavy rainfall events based on rainfall amounts provided by tipping bucket rainfall gauges are analyzed for 1960-2012 at 285 stations. The results show that extreme heat events, defined as days with at least one hourly humidex value above 30, have increased significantly at more than 36% of the stations, most of which are located south of 55°N; days with nighttime hourly humidex values remaining above 20 have increased significantly at more than 52% of the stations, most of which are located south of 50°N. Extreme cold events represented by days with at least one hourly wind chill value below −30 have decreased significantly at more than 76% of the stations across the country. No consistent changes were found in heavy rainfall events. Because city residents are very vulnerable to severe weather events, detailed results on changes in extreme heat, extreme cold, and heavy rainfall events are also provided for ten urban centres.RÉSUMÉ [Traduit par la rédaction] Nous examinons les tendances observées de conditions météorologiques extrêmes, selon les alertes destinées au public qu'émet Environnement Canada, et ce, en analysant pour la période allant de 1953 à 2012, les événements de chaleur ou de froid extrêmes, à l'aide des indices humidex et de refroidissement éolien à 126 stations climatologiques. Nous étudions l'évolution des cas de pluie abondante en comparant les accumulations de précipitations qu'ont enregistrées les pluviomètres à auget, à 285 stations, de 1960 à 2012. Les résultats montrent que les cas de chaleur extrême, définis comme étant les jours où au moins une valeur horaire de l'humidex est supérieure à 30, ont augmenté de façon significative à plus de 36% des stations, dont la plupart se situent au sud de 55°N. Le nombre de nuits où l'humidex horaire demeure supérieur à 20 a augmenté significativement à plus de 52% des stations, dont la plupart se trouvent au sud de 50°N. Les cas de froid extrême, représentés par les jours où au moins une valeur horaire du refroidissement éolien descend sous −30, ont diminué significativement à plus de 76% des stations situées partout au pays. Nous n'avons détecté aucun changement cohérent dans les cas de pluie abondante. Comme les citadins demeurent très vulnérables aux conditions météorologiques extrêmes, nous présentons des résultats détaillés sur la tendance des occurrences de chaleur et de froid extrêmes, ainsi que de pluie abondante, pour dix centres urbains.

Climate change and Canada’s north coast: research trends, progress, and future directions

“…Significant uncertainties and knowledge gaps remain, however. Model disagreements arise from uncertainty about greenhouse gas emissions, parameterization of physical processes (e.g., snow sublimation or Antarctic ice melt rates), and model structure variance (e.g., resolution, constants) (Hodson et al 2013;Mekis et al 2015). While models continue to improve, it is important to note why uncertainties arise and what the resulting ranges of climate projections mean for communities and policy makers.…”

“…While models continue to improve, it is important to note why uncertainties arise and what the resulting ranges of climate projections mean for communities and policy makers. Precipitation models continue to offer wide confidence intervals at regional levels, particularly when examining multi-variable conditions, such as blizzard conditions (snow-water equivalent, wind, and surface temperatures are all factors) (Mekis et al 2015). Sea level rise projections are complicated by uncertainty about the stability of the Antarctic ice sheet, with additional tens of centimeters of sea level rise possible (Deconto and Pollard 2016;James et al 2015;Mekis et al 2015).…”

“…Precipitation models continue to offer wide confidence intervals at regional levels, particularly when examining multi-variable conditions, such as blizzard conditions (snow-water equivalent, wind, and surface temperatures are all factors) (Mekis et al 2015). Sea level rise projections are complicated by uncertainty about the stability of the Antarctic ice sheet, with additional tens of centimeters of sea level rise possible (Deconto and Pollard 2016;James et al 2015;Mekis et al 2015). Further, there are knowledge gaps surrounding the impacts of Atlantic Ocean heat exchange on sea ice melt, regional permafrost thaw projections are limited at community scales, and there continue to be challenges in modeling future surface wind dynamics (useful for aviation among other industries) (Stroeve et al 2012).…”

Recent climatic, cryospheric, and hydrological changes over the interior of western Canada: a review and synthesis

“…Temporal variations of regional heavy precipitation displayed strong inter-decadal variability with limited evidence of long-term trends over the latter part of the 20th century, except in the number of heavy snowfall events in fall and winter, which increased over all of northern Canada. Mekis et al (2015) found little evidence of changes in heavy rainfall events (accumulated rainfall > 10, 25, and 50 mm over periods of 1, 24, and 48 h, respectively) for the region over the period 1960-2012. They noted that there is no apparent regional pattern in such extreme events because they are highly localized and the station density is relatively low.…”

“…Other indices showed mostly mixed, non-significant trends. Mekis et al (2015) examined trends in extreme heat and extreme cold events (days with at least one hourly humidex value above 30 and with at least one hourly wind chill value below −30, respectively) from 1953 to 2012 at 126 stations across Canada. They found that extreme heat events had increased significantly at many of the stations across Canada and extreme cold events had decreased significantly at virtually all stations.…”