Droughts and rainfall in south-eastern Finland since AD 874, inferred from Scots pine ring-widths

Early summer (May–June) precipitation variability was reconstructed for south-eastern Finland using a millennia-long (from 874 to present day) ring-width chronology of Scots pine (Pinus sylvestris L.). A regression-based calibration model using tree-ring widths captured 31% of the variance in the observed precipitation record. The time stability of the reconstruction equations was studied by cross-calibration/verification. Additional verification was provided by a neighbouring weather station. Interannual variability as well as periods of abundant rainfall and drought are presented. The three most humid early summers occurred in 1090, 1094 and 1924, and the driest in 939, 943 and 1116. Prolonged periods of severe drought took place during 1173–1191, 1664–1680 and 1388–1402, and wet spells during 1081–1095, 1433–1447 and 1752–1765. Fast Fourier transform showed the most dominant cyclic behaviour on interdecadal time scales.