A physically based, coupled and distributed hydrologic model has been set up for the Ringkøbing Fjord catchment, Denmark. This transient model, built with the MIKE SHE/ MIKE 11 code, comprises all major components of the terrestrial water cycle, including a three-dimensional fi nite-diff erence groundwater model. The dynamic coupling of the hydrologic processes secures physically sound feedback and makes the model an ideal tool for evalua ng the overall water balance and quan fying poten al water balance issues. Historically, failure to obtain water balance closure has been a persistent and much debated problem in Denmark, presumably arising mainly from uncertain es in precipita on, actual evapotranspira on, and groundwater fl ow to the sea. In this study, the water balance issues were addressed within the modeling framework through analysis of diff erent rain gauge catch correc ons and poten al evapotranspira on input. The analysis focused on the eff ect of diff erent rain gauge catch correc ons on the model performance, the op mized parameter sets, and state variables not included in the model calibra on. The results suggest that water balance problems can be reduced by using a dynamic rain gauge catch correc on based on daily wind speed and temperature fi elds. The model op miza on and performance evalua on revealed, however, that several parameter sets gave similar performance compared with the observed groundwater head and river discharge data but s ll resulted in signifi cant diff erences with respect to internal water fl uxes such as evapotranspira on, groundwater recharge, and stream fl ow components. New observa onal data are needed to constrain the model further and thus reduce the water balance uncertain es convincingly.Abbrevia ons: ET, evapotranspira on; HOBE, Hydrological Observatory and Exploratorium; LAI, leaf area index; SVAT, soil-vegeta on-atmosphere transfer.A correct quan fi ca on of the water balance and its individual components (precipitation, evapotranspiration, river runoff , subsurface runoff , and storage change) is vital for water resources management (Wisser et al., 2010). Quantifi cation of these components relies on the availability of accurate hydrologic data and on the application of reliable hydrologic models. Accurate precipitation measurements are of particular importance, especially in the northern latitudes, where uncertainties are large due to undercatch of solid precipitation (Adam and Lettenmaier, 2003;Tian et al., 2007;Yang et al., 2005). Recent studies have documented the large uncertainty in precipitation estimated at global (Fekete et al., 2004;Legates, 1995) and continental scales (Tian et al., 2007;Walsh et al., 1998). Th ere are, however, few detailed modeling studies of the eff ect of precipitation accuracy and catch correction at local to regional scales.Problems are oft en encountered when modeling the water balance at the catchment scale (Arnold et al., 2000;Henriksen et al., 2003). Hydrologic models are typically calibrated against existing fi eld data, of wh...