Downscaling a national hydrological model to subgrid scale

The resolution of nation scale hydrological models is often considered a limitation with respect to providing useful management information on local scale issues. Use of these coarse scale models to inform both the structure and parameterisation of local scale models could potentially enhance their utility and in some cases provide initial estimates to local scale water resource issues such as nitrate transport. This study explores whether a finer resolution model, whose conceptualization and parameterisation are based upon a nation scale model, can replicate local scale water balance observations and in this way expand the utility of large-scale models. We use the Danish National Water Resources model (DK-model) as a template to model a small 5 km2 subcatchment in Denmark and compare the flows at four transect locations to those observed in a previous field investigation. The resolution of the DK-model is 500 m, and this model was refined to create four additional models of the subcatchment with 100 m, 50 m, 20 m, and 10 m resolutions. Results suggest that none of the refined models could accurately capture the daily overland and groundwater flow conditions. However, for the finer resolution models (10 m and 20 m), the annual overland and groundwater flows agreed well with the observed flows.