Long-term (100 years) trends, variations, and extremes for pertinent agroclimatic variables across southern Ontario

Long-term (100 years) climate records were studied for 6 locations across southern Ontario to explore evidence of changes in agriculturally pertinent climate variables over the last century, with particular attention to interannual variability and extremes, and to seek evidence of spatial differences in these changes. Average conditions, the amount of interannual variability, and the relative frequency of extreme events were compared before and after 1950 to determine if there was any evidence of a significant change in the selected agroclimatic measures of heat and moisture over the study period. These analyses demonstrated that those sites in the interior of the study region had a significant increase in the availability of heat. For trends in moisture conditions those sites in close proximity to large bodies of water showed the greatest increase in moisture availability. The analysis also indicated that there has been no significant change in the degree of year to year variation in the study region and no apparent spatial pattern in terms of changes in agroclimatic heat and moisture. Examination of changes in the frequency and magnitude of extreme events throughout the study period revealed that there was some change in the frequency of extremes with generally an increase in the occurrence of high and a decrease in low end extreme conditions for both heat and moisture.