The phenological calendar of Estonia and its correlation with mean air temperature

A phenological calendar with 24 phenological phases was compiled for three meteorological stations in Estonia for the period 1948-1996. We analysed the length of the vegetation period, the order of the phenological phases, and the variability and possible changes for two incremental climate change scenarios (+/-2 degreesC), and compared the results with examples of extreme years. The statistically significant linear trends show that the spring and summer-time phenological phases occurred earlier and the autumn phases moved later during the study period. The study of extreme (minimum and maximum) years shows that 70% of the earliest dates of the 24 phases studied have occurred during the last 15 years with an absolute maximum in 1990 with 8 extreme phases. The phenological spring has shortened (slope -0.23), the summer period has lengthened (slope 0.04), and the autumn has lengthened too. The length of the growing season, determined by the vegetation of rye, has shortened (slope -0.09), which could be the result of changing agricultural technology. The correlation between the starting dates of the phenological phases with the air temperature of the previous 2-3 months is relatively high (0.6-0.8). Studying the +2 degreesC and -2 degreesC scenarios and values for the extreme years shows that, in the case of short variations of air temperature, the phenological development remains within the limits of natural variation.