Water balance modelling in the Baltic Sea drainage basin - analysis of meteorological and hydrological approaches

Efforts to understand and simulate the global climate in numerical models h ave led to regional studies of the energy and water balance. The Baltic Bas in provides a continental scale test basin where meteorology, oceanography and hydrology all can meet. Using a simple conceptual approach, a large-sca le hydrological model of the water balance of the total Baltic Sea Drainage Basin (HBV-Baltic) was used to simulate the basinwide water balance compon ents for the present climate and to evaluate the land surface components of atmospheric climate models. It has been used extensively in co-operative B ALTEX (The Baltic Sea Experiment) research and within SWECLIM (Swedish Regi onal Climate Modelling Programme) to support continued regional climate mod el development. This helps to identify inconsistencies in bath meteorologic al and hydrological models. One result is that compensating errors are evid ent in the snow routines of the atmospheric models studied. The use of HBV- Baltic has greatly improved the dialogue between hydrological and meteorolo gical modellers within the Baltic Basin research community. It is concluded that conceptual hydrological models, although far from being complete, pla y an important role in the realm of continental scale hydrological modellin g. Atmospheric models benefit from the experience of hydrological modellers in developing simpler, yet more effective land surface parameterisations. This basic modelling tool for simulating the large-scale water balance of t he Baltic Sea drainage basin is the only existing hydrological model that c overs the entire basin and will continue to be used until more detailed mod els can be successfully applied at this scale.