Similarity criteria between full-scale and reduced-scale models for the urban heat dome flows study under calm and stable atmospheric conditions

City-scale buoyancy-driven flow is paramount for the dispersion of city pollutants and heat removal under calm and stable atmospheric conditions. Previous studies have assumed reduced-scale models can represent the characteristics of full-scale urban heat dome flows when the non-dimensional Froude number (Fr) is of similar magnitude after entering the Reynolds number (Re) independence regime. However, critical Re values were not well quantified for urban heat dome flows, especially in reduced-scale models. In this study, the influences of Fr, Re and a newly defined dimensionless number (m_Fr) on urban heat dome flows over an idealized square city were studied. A specific Re value (Re = 2.98 × 10⁵) is associated with a critical Fr value of 0.003, while a given Fr value (Fr = 0.013) corresponds to a critical Re value of 1.6 × 10³ in reduced-scale models. Noticeable diagonal inflow at lower levels and side outflow at upper levels forms when Fr [Formula: see text] 0.003 and Re [Formula: see text] 1.6 × 10³. When the newly defined <i>m</i>_Fr is used, side outflow angles and flow structures of urban heat dome flows for both full-scale and reduced-scale models agree well with each other. This indicates that <i>m</i>_Fr can be regarded as a suitable dimensionless number for the similarity criterion in urban heat dome flow studies.This article is part of the theme issue 'Urban heat spreading above and below ground'.