Long-term variations and trends in precipitation in Finland

Abstract

Annual, seasonal and monthly variations in precipitation during the period 1911–2011 were evaluated using spatially interpolated monthly precipitation records at 165 stations with more than 30 years of data (of which 32 stations had 101 years of data referring to full length of study period). Historical trends and cyclic patterns of precipitation and links to teleconnection indices were analysed. The results show that annual precipitation in Finland increased by 0.92 ± 0.50 mm year−1 (p < 0.05) during the study period (1911–2011), and showed negative relationships with the East Atlantic/West Russia (EA/WR) teleconnection pattern (ρ = −0.41, p < 0.05) through the years 1950–2011. However, there were spatial (north–south/east–west) differences between regions. The time cycle (λ) for annual precipitation cycles was estimated to 149 years (R2=0.15), and 1964 was indicated as the turning point from a negative (dry) to a positive (wet) phase. Analysis of seasonal and monthly cycles showed larger variations, depending mainly on teleconnection effects. Analysis of seasonal precipitation determined increasing trends for winter (by 0.46 ± 0.19 mm year−1) and summer (by 0.32 ± 0.29 mm year−1), while no clear trend was found for spring and autumn precipitation (p > 0.05). Winter precipitation was most strongly correlated with the North Atlantic Oscillation (NAO) index (ρ = 0.55, p < 0.05), while the EA/WR pattern was the most significant teleconnection index for precipitation variations in spring (ρ = −0.33, p < 0.05) and summer (ρ = −0.49, p < 0.05); the precipitation variability during autumn was negatively associated with the Scandinavia (SCA) pattern (ρ = −0.40, p < 0.05). The results clearly indicate that Finland has experienced wetter climate than normal conditions during recent decades, and precipitation in the Fenno-Scandinavian climate is controlled by a number of climate teleconnection indices, not just the NAO as previously assumed.