AGRICULTURAL METEOROLOGY: SOME CHARACTERISTICS OF PRECIPITATION IN SASKATCHEWAN AND ALBERTA

Abstract

A five-year moving average of autumn and winter (Sept. 1 to March 31) and spring and summer (April 1 to Aug. 31) precipitation showed undoubted variation with time over the years 1898–1934, periods of above- and below-average moisture alternating, though not with simple periodicity. There were in addition large irregular annual variations in the amounts recorded at individual stations.In spite of irregularities, to be expected in the limited sample of years available, the frequency distribution of seasonal precipitation at Edmonton, Calgary, Battleford and Swift Current showed no gross asymmetry, seasons with precipitation in the vicinity of the average being on the whole the more numerous. There were, however, qualitative differences in the frequency distribution of the annual amounts of rain in the five individual spring and summer months. Correlation studies revealed no consistent association between the amount of precipitation in different spring and summer months of the same year, or between the totals for the autumn and winter, and for the following spring and summer period.The average (1916–1932) percentage of days on which rain fell showed a distinct seasonal trend during spring and summer, being lowest in April and highest in June. Similar variation was noted in the average amount of rain per rainy day, which was also lowest in April and highest in June and July. In all five months the frequency distribution of the daily amounts (exclusive of zero) was decidedly skew, the smaller amounts being much the more numerous. The proportion of the total precipitation received in small daily amounts was on the average much increased during periods of subnormal rainfall.Although there was a significant correlation between the total precipitation at different stations in the same district during the same month, analyses of variance revealed that there was also considerable local variation in the four districts studied. The monthly amounts received in daily quantities exceeding 0.30 in. per day showed relatively even greater local variation than did the total precipitation. Consequently, the intensity of precipitation, as measured by the percentage of the monthly totals accruing from the larger daily falls, was also subject to appreciable local fluctuations.Some agricultural implications of these aspects of the weather are indicated.