Impacts of small scale rainfall variability in urban areas: a case study with 1D and 1D/2D hydrological models in a multifractal framework

Abstract

In this paper the sensitivity to small scale unmeasured rainfall variability (i.e. at scales smaller than 1 km by 1 km by 5 min in time, which are usually available with C-band radars) of a 1D/2D model with a 10 m resolution and a semi-distributed 1D model of the same 1.47 km² urban area is analyzed. The 1D/2D model is the open source numerical platform Multi-Hydro, which couples (open source) distributed models of involved hydrological/hydraulic processes. The methodology implemented to evaluate the uncertainties consists of generating an ensemble of realistic rainfall fields downscaled to a resolution of 12.3 m in space and 18.75 s in time with the help of a stochastic universal multifractal model. The corresponding ensemble of hydrographs is then simulated. It appears that the uncertainty is significant and that Multi-Hydro unveils much more uncertainty than the simpler 1D model. This points out a need to develop high resolution distributed modelling in urban areas.

Keywords::

• rainfall variability
• 1D/2D modelling
• multifractals
• space-time downscaling

Acknowledgements

The authors acknowledge Julien Richard (LEESU) for his help in facilitating and reworking the terrain and sewer network data. The authors acknowledge Météo-France for providing the radar rainfall estimates in an easily exploitable format, and especially Pierre Tabary and Valérie Vogt, and the “Direction Eau et Assainissement” of Seine-Saint-Denis for providing the 1D calibrated hydrological-hydraulic model of the Kodak catchment, flow measurements and helpful comments on the results.

Additional information

Funding

The authors greatly acknowledge partial financial support form the Chair “Hydrology for Resilient Cities” (sponsored by Veolia) of Ecole des Ponts ParisTech, EU FP7 SMARTesT project, EU NWE INTERREG IV RainGain Project (www.raingain.eu), and EU Climate KIC Blue Green Dream (www.bgd.org.uk).