Impact of climate change on the development of the islands of the Neris River (eastern part of the Baltic Sea basin)

The frequency of high floods is one of the most important factors shaping the riverbed and influencing other aspects, such as sediment transport and deposition, vegetation establishment and growth. The aim of this study is to assess the impact of climate change on the flood regime of the Neris River (eastern part of the Baltic Sea basin) and the related changes in river islands, morphometric indicators of the riverbed, and vegetation colonization. To identify changes in the hydrological regime of the river, water level measurement data from the Buivydžiai and Jonava hydrological stations were used. To assess vegetation coverage and the presence of islands in the Neris River, orthophotos at a scale of 1:10 000 from the years 2005–2006, 2012–2013, and 2018–2020 were analyzed. Using the ArcGIS ArcMap software package, river island area and island forest coverage were calculated. The results of the study show that during the observation period (2005–2020), in the lower course of the river, the area of the islands increased, and island forest coverage grew from 7% to 18%. Between 2005 and 2020, the water level in the lower course rose above 300 cm (above the station’s zero line) only twice. The absence of high floods creates favorable conditions for plants to colonize alluvial environments. Consequently, this may lead to extreme flood events in the future, caused by a restructured river channel following a prolonged period of low flood activity.