Improvements of the hydrological processes of the Town Energy Balance Model (TEB-Veg, SURFEX v7.3) for urban modelling and impact assessment

Abstract. Climate change and demographic pressure are common issues to be considered when conducting urban planning. Local authorities and stakeholders have therefore opted for more nature-based adaptation strategies, which are especially suitable to influence both hydrological and energy processes. Assessing the multiple benefits of such strategies on the urban microclimate thus requires effective numerical tools. This paper presents recent developments of the water budget in the TEB-Veg model (SURFEX v7.3), which allows for a better representation of the hydrological processes of urban subsoil. This new hydrological module has been called TEB-Hydro. The developments studied concern the introduction of subsoil underneath built surfaces, and the processes of: horizontally rebalancing intra-mesh soil moisture, draining soil water via the sewer network, and limiting deep drainage in the aim of achieving a more realistic base flow pattern in the sewer system. A sensitivity analysis is then performed in order to identify the hydrological parameters required for model calibration. The new TEB-Hydro model is evaluated on two small residential catchments in Nantes (France) by comparing simulated sewer discharges to observation findings. In both cases, the model tends to overestimate total sewer discharge and performs better under wet climate conditions, with a KGE statistical criterion greater than 0.80 vs. roughly 0.60 under drier weather conditions. Yet these findings remain encouraging since the same set of model parameters are identified for both catchments, irrespective of meteorological and local physical conditions. This approach opens opportunities to apply the model at the city scale with respect to projections of climate and demographic changes.