Climate Downscaling Processes Using WRF/Chem and CALMET Modelling Systems: Madrid Case Study

Downscaling techniques are very important to assure the robustness and credibility of climate modelling exercises. Regional climate simulations use boundary conditions and initial conditions from global climate and meteorological models. The regional climate simulations (WRF/chem model) have much higher spatial resolution and using nesting approaches can be used to derive climate indicators at urban level. Dynamical nesting approaches -- also known as dynamical downscaling procedures -- use a substantial amount of computer power, particularly for urban applications, other alternatives such as CALMET diagnostic model (for meteorological applications) and CMAQ model (with linear chemistry) produce results faster and can be used for climate applications with reasonable required computer power. In this contribution, we are using the European Centre for Medium-Range Weather Forecasts (ECMWF) model data sets to provide boundary conditions for the mesoscale model WRF/Chem (NOAA, US) that has been ran over Europe with 23 km spatial resolution and 33 vertical levels up to 50 hPa. We have used the full nesting approach defined into WRF model to produce simulations centered over the city of Madrid (Spain) with 4.6 km spatial resolution (nesting level 1, l1), 0.92 km spatial resolution (nesting level 2, l2) and 0.184 km spatial resolution (nesting level 3, l3). In l3, we have run the CMAQ (full chemistry) model (EPA, US) to produce chemical pollution data. We have applied both downscaling techniques over Madrid area using Retiro meteorological and air pollution monitoring station as observational station. The comparison between both downscaling techniques shows that CALMET-CMAQL (linear chemistry) model is much faster and the results are good enough (compared with other simulations results) to consider this tool, when the number of simulations for climate purposes is very high (due to many years and several climate scenarios) and the application of the WRF/chem model (dynamica- downscaling) is prohibited computationally.