Spatial resolution considerations for urban hydrological modelling

Hydrological model simulations can be applied to evaluate the performance of low impact development (LID) tools in urban areas. However, the assessment for large-scale urban areas remains a challenge due to the required high spatial resolution and limited availability of field measurements for model calibration.
This study proposes a methodology to parameterize a hydrological model (SWMM) with sufficiently high spatial resolution and direct accessibility of model parameters for LID performance simulation applicable to a large-scale ungauged urban area. Based on calibrated high-resolution models for three smallscale
study catchments (6–12 ha), we evaluated how constraints implied by large-scale urban modelling, such as data limitations, affect the model results. The high-resolution surface representation, resulting in subcatchments of uniform surface types, reduced the number of calibration parameters. Calibration conducted
independently for all catchments yielded similar parameter values for same surface types in each study catchment. These results suggest the applicability of the parameter values calibrated for high resolution models to be regionalized to larger, ungauged urban areas. The accessibility of surface specific model parameters for LID simulation is then also retained. Conducted perturbations in spatial resolution through sewer network truncation showed that while the runoff volume was mostly unaffected by resolution perturbations, lower resolutions resulted in over-simulation of peak flows due to excessively rapid catchment response to storm events. Our results suggest that a hydrological model where parameter values are adopted from high-resolution models and that is developed based on a minimum conduit diameter of 300 mm provides good simulation performance and is applicable to large-scale urban areas with reasonable effort.