CR 22:27-39 (2002)  -  doi:10.3354/cr022027

Net precipitation over the Baltic Sea during present and future climate conditions

Anna Rutgersson*, Anders Omstedt, Jouni Räisänen

Rossby Centre, SMHI, 60176 Norrköping, Sweden

ABSTRACT: By using a process-oriented ocean model forced with data from a gridded synoptic database, net precipitation values (precipitation minus evaporation) over the Baltic Sea are obtained. For a range of realistic meteorological forcing the average annual value obtained from an 18 yr (1981-1998) simulation ranges between 1100 and 2500 m3 s-1. The monthly variations are significant with the highest values occurring in early summer and even negative values in late autumn. Ice is an important factor, and the net precipitation is close to zero in the southern basins with no ice. Calculated net precipitation for a 98 yr period (1901-1998) using river runoff and maximum ice extent indicates that the investigated 18 yr period was wetter than the almost 100 yr climate mean. A realistic climate estimate of net precipitation during the 20th century is estimated to be 1500 ± 1000 m3 s-1. The evaluation of 2 present day regional climate simulations indicated high precipitation, low evaporation, and thus excessive net precipitation compared to the climate estimate from this investigation. When simulating the effect of increased greenhouse gases, the change in net precipitation was positive but small due to the compensating effects of increased precipitation and increased evaporation associated with increased temperature and reduced ice.

KEY WORDS: Water cycle · Baltic Sea · Precipitation · Evaporation · Climate

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