Analyses of growing degree-days for agriculture in Atlantic Canada

Growing degree-days (GDD) above base temperatures of 0, 5 and 10C provide a useful indicator for assessing seasonal crop development in the Atlantic region of Canada. GDD statistics can be useful for a variety of agricultural management decisions. This study presents seasonally accumulated average values of GDD above 5C for all geographic regions of Atlantic Canada based on data from the 30 yr period 1956 to 1985. Values ranged from a high exceeding 1800 GDD in several areas of the Maritimes to less than 800 for the northern tip of Newfoundland. 'Rules of thumb' procedures were established for estimating the probability that selected threshold GDD values were exceeded and for estimating accumulated GDD at selected probability levels for all 3 base temperatures. Average accumulated GDD for base temperatures of 0C and 10C were highly correlated with values for 5C (r2 2 0.97). Available GDD at probability levels of 5, 10 and 25% were related to the mean accumulated GDD for all 3 base temperatures using linear regression relationships (r2 2 0.97). Also, the probability of exceeding selected threshold values of accumulated GDD were related by second order regression functions (r2 2 0.84) to the average GDD for each base temperature. By using these regression relationships, mean GDD > 5OC can be used to estimate GDD over a range of probabilities and probabilities for a range of GDD thresholds for 0, 5 and 10C base temperatures.