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Abstract

In this study, a hydrological discharge model is presented which may be applied as a tool to
validate the simulation of the hydrologic cycle of atmospheric models that are used in climate
change studies. It can also be applied in studies of global climate change to investigate how
changes in climate may affect the discharge of large rivers.
The model was developed for the application with the climate models used at the Max-Planck-
Institute for Meteorology. It describes the translation and retention of the lateral waterflows on
the global scale as a function of the spatially distributed land surface characteristics which are
globally available. Here, global scale refers to the resolution of 0.5° and lower, corresponding
to a typical average gridbox area of about 2500 km2. The hydrological discharge model
separates between the flow processes of overland flow, baseflow and

overflow. The model

parameters are mainly functions of the gridbox characteristics of topography and gridbox
length.
The hydrological discharge model is applied to the BALTEX (Baltic Sea Experiment) region
using input from an atmospheric general circulation model (ECHAM4) as well as from a
regional climate model (REMO). The simulated inflows into the Baltic Sea and its sub-
catchments are compared to observed and naturalized discharges. The results of this
comparison are discussed and the simulated values of precipitation, surface air temperature and
accumulated snowpack are compared to both observed data and surrogate data.