LONG-TERM (100 YR) CLIMATIC TRENDS FOR AGRICULTURE AT SELECTED LOCATIONS IN CANADA

Long term (100 yr) trends of 17 selected annual climatic parameters were studied for 5 locations in Canada. Simple linear correlation coefficients (r) were computed for each variable with time. Temporal variations were not uniform over space, as might be expected over a large continent. Some variables differed significantly with time, while others did not. Forage aridity indices (FAI), or seasonal forage water deficits, had significant negative r values at Agassiz and Ottawa, indicating decreasing aridity over time, but no such trends were evident at the other 3 locations. Stations in western Canada were characterized by r values (mostly significant at P = 0.01) which indicated trends to earlier last spring frost (SF), later growing season end (GSE), later first fall frosts (FF) and increased frost-free period (FFP), growing degree-days (GDD) and Corn Heat Units (CHU). Stations in eastern Canada did not exhibit the same warming trends. No warming trends were observed in January mean temperature (JAN). Five-year moving averages and standard deviations were calculated and plotted for FAI, FF, GDD and GSL (growing season length). The climatic attributes were extremely variable. making detection of warming or cooling trends difficult. The FAI for the last 30 yr or more at Agassiz and for the last 20 vr at Ottawa was well below the 100 vr normal. At Indian Head, FAI values were high during the 1930's and again around 1960, reflecting the drought conditions which occurred at those times. The other 3 variables showed a tendency to slightly increasing values over the past 50 yr at Agassiz, Indian Head, Brandon and Ottawa. Little, if any, systematic change in these elements was evident at Charlottetown. Standard deviations (S(d)) fluctuated widely at all locations, with generally little evidence to suggest that the climate has become more or less variable. Cumulative frequency distribution for the total period and the first 70 yr were compared to the last 30 yr. There was an increased frequency of lower FAI values at 2 locations for the 30-yr period. GDD increased significantly at lower probabilities at Indian Head. Differences in frequency distributions were generally slight for all other variables at the 5 locations.