Variability in dryness and wetness in central Finland and the role of teleconnection patterns

Interannual variability in meteorological dryness and wetness in central Finland during the period 1959–2009 was analysed using Standardized Precipitation Index (SPI) on three timescales (annual, seasonal and monthly). For different time steps (12, 3 and 1 months) of SPI values (SPI12, SPI3 and SPI1), trends based on the Mann-Kendall non-parametric test and the most significant relationships with a number of climate teleconnection patterns based on Spearman correlation coefficient (rho) were determined. Analysis of the SPI values on different timescales showed a general decreasing trend in dryness and an increasing trend in wetness; only August showed an increasing trend in dryness. The longest wet period observed was 5 years (between 1988 and 1992), while the longest dry period was 4 years (in the mid-1960s). Wet conditions were more frequent than dry conditions and mainly occurred at extreme or moderate level. Typically, the extremely wet level was more frequent than the extremely dry level. The dry and wet conditions were negatively correlated with the East Atlantic/West Russia and Scandinavia teleconnection patterns and positively correlated with the North Atlantic Oscillation.