Changes in water discharges of the Baltic states rivers in the 20th century and its relation to climate change A. Reihan 1 *, T. Koltsova 2 , J. Kriauciuniene 3 , L. Lizuma 2 and D. Meilutyte-Barauskiene 3 1 Institute of Environmental Engineering, Tallinn University of Technology, Ehitajate tee 5, EE-19086 Tallinn, Estonia. *Corresponding author. E-mail: alvina.reihan@ttu.ee 2 Latvian Hydrometeorological Agency, 165 Maskavas Str., Riga, LV-1019, Latvia 3 Laboratory of Hydrology, Lithuanian Energy Institute, Breslaujos 3, LT-44403 Kaunas, Lithuania Received 18 December 2006; accepted in revised form 22 August 2007 Abstract The river discharge changes in three Baltic States and its relation to changes in the main climatic variables such as precipitation and air temperature were analyzed using observed data and methods of empirical statistical analysis. The study is important for the development of efficient water resource management systems and validation of climate change impact models. The application of the Mann-Kendall test reveals that a significant increasing trend in winter air temperature and precipitation was determined for all 3 investigated periods (1923–2003, 1941–2003 and 1961–2003). The same trend was found for the winter and annual discharge time series. No trend was observed for the spring, summer and autumn seasonal streamflow and summer low flow series for most of the Baltic region. In general the relation between the main meteorological and hydrological parameters and the tendency in river discharge trends is common for all of the Baltic States, and might be associated with the regional impacts of global climate change. Keywords Baltic States; climate change; long-term variability; river discharge trends Introduction Large-scale weather patterns associated with pressure systems are an important factor influencing the total amount of precipitation and its spatial and seasonal distribution over central and eastern Europe (Dayan and Lamb 2005). These weather patterns may change with the changing climate and will in turn affect the water resource availability. During recent decades, considerable attention has been paid to the study of global climate change (IPCC 2001) and how changes in the hydrological time series can be related to climate change (Kite 1993; Hiltunen 1994; Arnell and Reynard 1996) and its regional impacts (Gleick 1986). Trends in river discharge have been extensively analysed. For example, an increasing trend in river discharge was found in the USA (Lins and Slack 1999) and, at the same time, a decreasing trend in river discharge was found in northern Canada (Dery and Wood 2005). The impact of climate change on river discharge has been identified in the Nordic countries as well (Bergstrom et al. 2001; Hisdal et al. 2003; Lindstro ¨m and Alexandersson 2004; Roald et al. 2006). Vehvila ¨inen and Lohvansuu (1997) state that in Finland climate change may increase the mean discharge of rivers by 20 – 50%. The possible increase of Danish river discharge (by 12%) is described by Thodsen (2007). Changes in river discharge of the Baltic States have also been investigated in individual national studies. The Latvian studies conclude that changes of discharge are minimal and significantly increased only for the main rivers (Klavins et al. 2002). Changes in the water balance structure of Lithuanian rivers under different climate change scenarios are investigated by doi: 10.2166/nh.2007.020 Nordic Hydrology Vol 38 No 4–5 pp 401–412 q IWA Publishing 2007 401 Downloaded from https://iwaponline.com/hr/article-pdf/38/4-5/401/364841/401.pdf by guest on 12 June 2020