The power of models in planning: the case of DaisyGIS and nitrate leaching

Spatial deterministic simulation models such as DaisyGIS are increasingly being used for decision‐making in European planning. In Denmark specifically, there is an increasing interest at the regional level to use DaisyGIS as an administrative tool. There are, however, uncertainties associated with the use of these deterministic models, partly due to the spatial variation in input parametres. This study evaluates the use of DaisyGIS for nitrate leaching assessments based on nitrate leaching experiments carried out at the Marbjerg experimental site at Roskilde University. The study includes geostatistical analysis of soil and hydraulic variables and the use of remote sensing for deriving spatial information about the Leaf Area Index. It is found that the model predicts nitrate leaching well when using site‐specific input data but it is quite sensitive to the parameterization of carbon, the C/N ratio and variations in the Leaf Area Index (LAI). With the increasing use of Daisy in the counties, there is a need to find better ways of handling uncertainties in model output which can be used by decision‐makers and to study further the impact of spatial LAI assimilation on catchment scale nitrate leaching processes.