Characterizing temporal trends of meteorological extremes in Southern and Central Ontario, Canada

Forecasts of increased frequency of meteorological extremes have received considerable attention due to their potential impact on the integrity of biotic communities, stability of terrestrial and aquatic environments, availability of ecosystem services, and broader societal prosperity. Canada is projected to experience greater warming rates than many other regions of the world and changes in meteorological extremes are predicted to be variable across the country. In this context, our goal is to evaluate the long-term trends of extreme meteorological variables (air and dew point temperature, relative humidity, wind speed, and precipitation) in southern and central Ontario (from 42?degrees N to 50?degrees N), while considering the role dynamics of large-scale atmospheric oscillations (El Nino-Southern Oscillation, North Atlantic Oscillation, Arctic Oscillation, and Pacific Decadal Oscillation). Air temperature minima increased year-round, while temperature maxima mainly increased during the cooler months of the year. Consistent with recent evidence from the literature, our study identified an increase in the amount of atmospheric water since the 1950s, as shown by the rising trends in dew point temperature maxima and minima during winter and mid-summer/early-autumn, respectively. Likewise, we found a weak decline in the relative humidity during the warm season, and a more discernible declining trend during the cooler part of the year, which could be in turn reflective of the moderate change of temperature maxima and rising minima, respectively. Consistent with the broader evidence of a global terrestrial stilling, our analysis showed a declining occurrence of high wind-speed events across the entire study domain, and more frequent slow-wind speeds during both warm and cold periods of the year. Interestingly, a closer examination of temporal trends in calm wind frequency provides evidence of a recent reversal in the latter trend with diminishing prevalence of very calm wind conditions. We generally found a weakly increasing temporal trend with maximum total daily precipitation, but without a coherent spatial pattern within the broader study area. Our analysis showed that large-scale phenomena have a discernible signature mostly on air temperature and humidity variables, but had little impact on low relative humidity, high and low wind-speed, and precipitation variability. Given the modest impact of teleconnections on long-term temporal trends, our study concludes that the meteorological extremes are more directly influenced by regional and local heat and humidity balance processes rather than global-scale atmospheric circulation. The observed trends of air temperature, humidity, and wind speed extremes suggest a profound impact on the phenology of aquatic and terrestrial ecosystems and human experience of weather.