Analysing the variability and trends of precipitation extremes in Finland and their connection to atmospheric circulation patterns

Ten precipitation indices recommended by the Expert Team on Climate Change Detection and Indices were used to analyse spatial distribution and temporal changes in annual amount, intensity, frequency and duration of precipitation statistics based on daily data with a focus on extremes in Finland during 1961-2011. Also, the connections between these high resolution (10 km) precipitation indices and six influential atmospheric circulation patterns (ACPs) for climate variability in Finland were studied. On the country scale, the results suggest significant increases in the amount and intensity of precipitation extremes, more precipitation days, and no clear changes in wet and dry spells. Both intensity and frequency of precipitation extremes over Finland decrease from south and southwest to north. The only exception is the distribution of precipitations days which is generally more frequent over eastern and upper areas of northern Finland. Wet (dry) spells were typically longer in the western (eastern) part of Finland. Significant increases in annual total wet-day precipitation, very wet days precipitation and simple daily intensity index were found over most parts of Finland during 1961-2011. Increasing trends in both extremely wet days and maximum 1-day precipitation were mostly observed in western, eastern, central and northern Finland. Such spatial pattern was also identified for significant increases in the frequency of heavy and very heavy precipitation days. The precipitation days increased over small parts of western, eastern and northern Finland. Wet spells showed lengthening trends in several grids over southwestern Finland, while dry spells lengthened in some areas over the entire country except southern parts. These variations in precipitation statistics were found to be significantly correlated with the East Atlantic/West Russia, East Atlantic, Scandinavia and Polar patterns.