Simulated sea level in past and future climates of the Baltic Sea

Abstract

Sea levels of the Baltic Sea in past and future climates were investigated based upon 6-hourly regional model results. For the future climate, the Rossby Centre Atmosphere Ocean model was used to perform a set of 30 yr time slice experiments. For each of the 2 driving global models HadAM3H and ECHAM4/OPYC3, one control run (1961 to 1990) and 2 scenario runs (2071 to 2100) based upon the scenarios A2 and B2 of the Special Report on Emission Scenarios (SRES) were conducted. To estimate uncertainties in the global and regional models, 3 sea level scenarios for the Baltic Sea were compiled assuming global average sea level rises between 0.09 and 0.88 m and considering land uplift and the impact of regional changes in wind direction and velocity from the time slice experiments. In the scenarios forced with ECHAM4/OPYC3 the mean sea level between October and April increases significantly compared to the control climate, and storm surges increase even more than monthly mean sea level. In the scenarios forced with HadAM3H the changes are mostly not significant. Depending on the sea level rise, the risk of flooding at the coasts may either decrease in the entire Baltic, or it may increase, especially at the eastern ends of the Gulf of Finland and Gulf of Riga and in Gdansk Bay. Here, maximum changes of about 1 m are found in the winter mean 99% quantiles of the sea level. For the past climate the regional ocean model was forced with reconstructed surface wind fields for 1903 to 1998. The results are close to observations, but storm surges in the western Baltic are underestimated. © Inter-Research 2004.