Long-term changes in hydrological regime of the lakes in Latvia

Abstract

Changes in the hydrological regime of the lakes of Latvia depend on natural and anthropogenic causes. This publication summarises the results of the research on the long-term changes in the water level, thermal and ice regimes in the seven largest lakes of Latvia: Liepājas, Usma, Ķīšezers, Burtnieks, Rāzna, Sventes and Lielais Ludzas, and their regional specifics from 1926 to 2002. For most of the studied lakes, the water level has been regulated, except for the lakes Liepājas, Burtnieks and Ķīšezers. Global climate warming has caused considerable changes in the hydrological regime of the lakes during the last decades and the surface water temperature has increased. At the same time, the number of days with ice cover and the thickness of ice have decreased. A positive trend in the freezing date and a statistically significant negative trend for the ice break-up date was found for all lakes. The lakes Liepājas and Usma are located in the western part and Lake Kīšezers in the central part, therefore their hydrological regime, in particular, the thermal and ice regime, differs from the lakes Burtnieks, Rāznas, Sventes and Lielais Ludzas which are located in the northern and south-eastern part of Latvia.