If the Belt and the Sound were closed, the sea level would change by 114 cm due to land drainage, by 58 cm from precipitation and by -48 cm from evaporation, each year, calculated for the whole surface of the Baltic which is 386700 km2. The net gain is 124 cm per year or a rise of about 0.3 cm per day.
The inflows have very little effect on daily sea level observations since water flows continually out through the Danish Straits.