Impact of Model Resolution on Urban Heat Island Simulation evaluated using Surface and Satellite Observations

Urban climate simulations with mesoscale numerical weather prediction (NWP) models are usually performed at rather coarse (> 1 km) resolution as a compromise between computational cost and accuracy. However, at such low resolution the heterogeneous urban environment and the interactions between the urban heat island (UHI) and the mesoscale circulation may not be sufficiently well represented.

In order to explore the impact of model resolution on urban heat island simulation, the mesoscale NWP model COSMO in climate mode (CCLM) is used at various horizontal resolutions down to 250 m. CCLM is coupled to the Double Canyon Effect Parametrization (DCEP) model, which is a multi-layer urban canopy model based on the Building Effect Parameterization (BEP). The simulations are performed for the medium-sized city of Zurich (Switzerland) for an intense heat wave event in summer 2015. The model results are evaluated using 2-m temperature (T2) data from urban surface observations and satellite-derived surface temperature from the Moderate-Resolution Imaging Spectroradiometer (MODIS) instrument. The former allows us to evaluate the impact of model resolution on the modelled T2 temporal evolution, whereas the latter is used to assess the spatial pattern of the UHI.

Results indicate a substantial impact of model resolution on urban climate modelling performances, with higher accuracy at higher resolution. Specifically, the spatial distribution and intensity of the simulated UHI significantly change with model resolution.