ON THE FREQUENCY OF PRECIPITATION-DAYS IN CALGARY,CANADA

Results of analyses of 86 years of precipitation records for Calgary, Canada, showed that there were three periods of above normal precipitation and three periods of precipitation significantly below normal. This pattern gave the precipitation climate a quasi-periodic appearance. The average number of precipitation-days was 134 per annum. The reduction in the frequency of precipitation-days in dry years was not as significant as the equivalent reduction in precipitation amounts. A significant upward trend in the frequency of precipitation-days, which correlated with a similar trend in cloud cover, was not repeated in precipitation amounts. The upward trend in both cloud cover and precipitation-day frequency is believed to be related to urban growth and the corresponding heat island. This enhancement is more pronounced in the fall and winter months than in the spring and summer.