Coupled hydrological and hydrodynamic modelling application for climate change impact assessment in the Nemunas river watershed–Curonian Lagoon–southeastern Baltic Sea continuum

Abstract

We analyse the cumulative impacts of climate change in a complex basin–lagoon–sea system continuum, which covers the Nemunas river basin, Curonian Lagoon, and the southeastern part of the Baltic Sea. A unique, state-of-the-art coupled modelling system was developed using hydrological and hydrodynamic models. The results of four regional downscaled models from the Rossby Centre high-resolution regional atmospheric climate model have been bias-corrected using in situ measurements and were used as forcing to assess the changes that the continuum will undergo until the end of this century. Results show that the Curonian Lagoon will be subjected to higher river discharges that in turn increase the outgoing fluxes into the Baltic Sea. Through these higher fluxes, both the water residence time and saltwater intrusion into the lagoon event frequency will decrease. Most of these changes will be more pronounced in the northern part of the lagoon, which is more likely to be influenced by the variations in the Nemunas river discharge. Its delta area may be susceptible to flooding as a result of the elevated discharge during winter. The southern part of the lagoon will experience lesser changes. While water temperatures in the entire lagoon and the southeastern Baltic Sea will steadily increase and salinity will decrease, the foreseen changes in the physical characteristics will not cause significant shifts in the ecosystem functioning but may affect the nutrient retention capacity. However, some ecosystem services such as ice fishing are expected to vanish completely due to the loss of ice cover.