The variability of long-term runoff series in the Baltic Sea drainage basin

Studying the variability of long-term runoff series is important in order to learn about the effects of climate change and human activity. The results of such analyses depend on the availability of long-term data. Long-term runoff data variability (annual, highest and lowest monthly discharge) was investigated in five rivers (the Nemunas, Neva, Oder, Vistula and Luleaelven) of the Baltic Sea drainage basin. These rivers have long-duration data. The discharge time series in the Nemunas at Smalininkai are the oldest data (1812-2009) and are related to the runoff in Europe and the Baltic Sea region as well. The other investigated rivers have discharge time series longer than one century. Long-term variability of annual discharge (the dry and wet phases of water flow) are common in the Nemunas, Neva, Vistula and Oder. One dry or wet phase continues for about 13-13.5 years and the whole period of variability is 26-27 years. The changes in the highest and lowest monthly discharges for the major rivers in the Baltic Sea drainage basin have been studied using the analysis of trends and anomalies expressed by percent from the reference period. Similar variability in the river runoff was found in the Nemunas, Neva, Vistula and Oder.