Correlation between spring phenophases and north atlantic oscillation index in Slovenia

Abstract

The influence of North Atlantic Oscillation on spring phenology in Slovenia has been analysed in this study. The NAOI trends of the early spring towards more positive values and hence stronger zonal flow during the last 20 years has been clearly reflected by an earlier onset of spring phases. Phenological and meteorological data for the period 1955-2000 were used in our study. Eight stations were selected: Celje, Ilirska Bistrica, Lesce, Ljubljana, Maribor, Murska Sobota, Novo mesto and Rateče, which represent at the same time phenological and meteorological stations. Twelve plants were chosen to represent three groups of phenological objects: wild herbaceous plants (snowdrop, dandelion, spring-saffron), forest trees and shrubs (common silver birch, beech, common elder, horse-chestnut, goat willow, hazel, large-leaved lime, common lilac), and fruit trees (plum tree). Environmental Agency of Republic of Slovenia provided phenological (leaf unfolding, beginning of flowering, full flowering) and meteorological data. The correlation between winter North Atlantic Oscillation Index (NAOI) and temperature is highly significant for all stations for the months from December to March, the average correlation coefficient is +0,58. With NAOI variability we explained the large part of variation in flowering phases of early-spring plants like dandelion, pussy willow and hazel. Correlations are weaker for late-spring phenophases. The values of all correlation coefficients are negative in all cases.