SENSITIVITY TO SPACE AND TIME RESOLUTION OF A HYDROLOGICAL MODEL USING DIGITAL ELEVATION DATA

The space and time resolutions used for the input variables of a distr ibuted hydrological model have a sufficient impact on the model result s. This resolution depends on the required accuracy, experimental site and the processes and variables taken into account in the hydrologica l model. The influence of space and time resolution is studied here fo r the case of TOPMODEL, a model based on the variable contributing are a concept, applied to an experimental 12 km2 catchment (Coet-Dan, Brit tany, France) during a two month winter period. A sensitivity analysis to space and time resolution is performed first for input variables d erived from the digital elevation data, secondly for the optimized val ues of the TOPMODEL parameters and finally for modelling efficiency. T his analysis clearly shows that a relevant domain of space and time re solutions where efficiency is fairly constant can be defined for the i nput topographic variables, as opposed to another domain of larger res olutions that induces a strong decrease of modelling efficiency. It al so shows that the use of a single set of parameters, defined as mean v alues of parameters on this relevant domain of resolution, does not mo dify the accuracy of modelling. The sensitivity of the parameters to s pace and time resolution allows the physical significance of the param eter values to be discussed.