Improved understanding of the impact of urbanization on the temperature, precipitation, and air quality of major eastern Canadian cities

Purpose: This study aims at identifying the impact of urbanization on urban climates of Eastern Canada. Methods: Gridded climate data were used over the 1988-2017 period to investigate inter and intra-annual trends of daily minimum and maximum temperatures and precipitation, within and outside the four largest cities of Eastern Canada (Montreal, Ottawa, Quebec City and Toronto). Results: Montreal was identified as the city where urbanization impacted temperature and precipitation the most. An urban heat island is particularly visible at night in summer and winter and has increased over the period. Urban precipitation has become less frequent and intense in the city compared to its rural surroundings, particularly during summer. The reduced capacity of cooling by precipitation reevaporation, and a modified albedo during winter, may have reinforced the urban heat island. Both rain and snow have a major impact on PM2.5 concentrations, particularly on the day following the meteorological event. Significance: Better awareness of the impact of urbanization on urban temperature and precipitation will improve our ability to predict the consequences of its acceleration on citizens' health, and to adapt our cities accordingly. To the best of our knowledge, no such study has yet been conducted in the region.