Urban features essentially influence atmospheric flow and microclimate, strongly enhance atmospheric turbulence, and modify turbulent transport, dispersion, and deposition of atmospheric pollutants (e.g., Piringer et al., 2007). Increased resolution in numerical weather prediction (NWP) models allows for a more realistic reproduction of urban air flows and air pollution processes, however most of the operational models still do not consider, or consider very poorly, the urban effects. This has triggered new interest in model development and investigation of processes specific to urban areas. Recent developments performed as part of the European project FUMAPEX on integrated systems for forecasting urban meteorology and air pollution (Baklanov et al., 2002(Baklanov et al., , 2005, the US EPA and NCAR communities for MM5 Bornstein et al., 2006;Taha 2008), WRF models , and other relevant studies (see e.g. Baklanov and Grisogono, 2007) have shown many opportunities in the "urbanization" of weather forecasting and atmospheric pollution dispersion models.Atmospheric models for urban areas have different requirements (e.g. relative importance of the urban boundary layer (UBL) and urban surface sublayer (USL) structure) depending on: (i) the scale of the models (global, regional, city, local, micro, etc.); (ii) the functional type of the model, e.g.:• Forecasting or assessment type of models, • Urban or regional climate models, • Research meso-meteorological models, • Numerical weather prediction models, • Atmospheric pollution models (city-scale), • Emergency preparedness models, • Meteo-preprocessors (or post-processors).A wide range of approaches have been taken to incorporating urban characteristics. In addition there are a wide range of processes which includes: characteristics of the urban canopy sublayer, components of urban surface energy balance (net radiation, sensible and latent heat fluxes, storage heat flux, etc.), and water v vi Introduction to the Problem and Aims transport. This results in a wide range of models (e.g., Brown and Williams, 1998;Oke et al., 1999;Grimmond and Oke, 1999;Kusaka et al., 2001; Masson, 2000;Dupont, 2001;Martilli et al., 2002). Most urban NWP or meso-meteorological models modify the existing non-urban approaches (e.g., the Monin-Obukhov similarity theory, MOST) for urban areas by parameterisation or finding proper values for the effective roughness lengths, displacement height, and heat fluxes, including the anthropogenic heat flux, heat storage capacity, albedo and emissivity change, etc. The main limitation is when there is a need to resolve meteorological profiles within the urban canopy, where the MOST assumption of a constant flux surface layer is invalid. This is obviously important as it is a layer into which pollutants are emitted and in which people live. The sophistication of urbanization within research mesoscale models has increased during the last 10 years, starting with the work of Brown and Williams (1998), which included urban effects in their TKE scheme. Masson ...