Attribution of Estonian phyto-, ornitho- and ichtyophenological trends with parameters of changing climate

We summarised trends of phyto-, ornitho- and ichtyophenological time series gathered during the last half a century in Estonia and analysed their relations with selection of climate parameters. 943 phenological time series with best observation quality from the period of 1948–1999 were selected for the analysis. Linear regression of phenological time series indicates that in total more than 80% of phenological phases have advanced during springtime. Significant values of phytophenological and ornithophenological phases have advanced 5–20 days and ichtyophenological phases have advanced 10–30 days. Estonian mean air temperature has become significantly warmer in spring and at the same time slight decrease in air temperature has been detected in autumn. Growing season has become significantly longer in the maritime climate area in West-Estonia. Analysis of attribution of phenological trends indicates that studied trends of phenophases and climate parameters are first and foremost related to changes of North Atlantic Oscillation Index (NAOI) during winter months (Jan–March). Correlations between them reach up to the level of 0.9. Although the impact of winter NAOI on the phases decreases towards summer, the trends of studied phases still remain high. Apparently trends of later phases and climate parameters are not affected only by changes of winter NAOI as since April and May other air masses coming from Eastern directions are dominating in the area of the Baltic Sea. These circulation indexes do not have significant changes during study period. Therefore the reasons behind the trends of phenophases in the end of spring and beginning of summer are elsewhere, like in temperature inertia caused by changing winter and spring and direct consequences of human impact like land use, heat islands or pollution.