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°C), 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°C and –2°C 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. Received: 29 November 1999 / Revised: 15 May 2000 / Accepted: 16 May 2000