Historical spatial and temporal climate trends in Southern Ontario, Canada

Spatial and temporal trends in historical temperature and precipitation extreme events were evaluated for Southern Ontario, Canada. A number of climate indices were computed using observed and regional and global climate data sets for the region over 1951-2013 period. A decrease in the frequency of cold temperature extremes and an increase in the frequency of warm temperature extremes was observed in the region. Overall, the number of extremely cold days decreased and hot nights have increased. Nighttime warming was greater than daytime warming. The annual total precipitation and the frequency of extreme precipitation also increased. Spatially, for the precipitation indices, no significant trends were observed for annual total precipitation and extremely wet days in the southwest and the central part of Ontario. Regarding temperature indices, cool days and warm night have significant trends in more than 90% of the study area. Generally, spatial variability of precipitation indices is much higher than of temperature indices. In terms of comparison between observed and simulated data, results showed large differences for both temperature and precipitation indices. For this region, the regional climate model was able to reproduce historical observed trends in climate indices quite well as compared to global climate models. The statistical bias-correction method generally improved global climate models ability to accurately simulate observed trends in climate indices.