Estimation of the formation and evolution of surface temperatures in the urban canopy layer: using SOLENE model and its assessment

The features of the urban area and its oblique and heterogeneous elements control the formation of surface temperatures (Ts) and better understanding these controls is important to elucidate the relationships between urban structures and their associated thermal behaviour together with the evolution of Ts. Through the use of SOLENE model it is possible to simulate the micro-scale thermo-radiative transfers within urban fragments and the restitution of thermal infrared radiative fluxes toward the sky. In the case study of Nantes, France, urban fabrics have been modelled into triangular meshed fragments with variable dimensions. Every facet of these meshed grids has been attributed its own used materials and thermal properties, by which an energy balance is estimated. Thermal signatures in various surface types have been elucidated in a spatio-temporal dimension and are evaluated by using in situ observations. The formation and evolution of Ts over the city centre have been investigated by using FLIR thermal infrared (TIR) camera, by which Ts was measured in a time series (1 hour interval). Using a scatter plot analysis the Ts changes were detected in various surface types and geometrical structures, which, depending upon the features and thermal properties, have then been extracted as polygons in TIR images. Time series and statistics of the selected polygons Ts are analysed. The measured Ts diurnal cycles are used to further validate the model SOLENE. The good agreement of the model outputs with the measurements show that the SOLENE simulation takes into good account of (1) the thermo-radiative interaction processes of the urban fragments, (2) the parametrical relations between geometrical features of urban fragments and thermal signatures: physical, aero-dynamical and radiative temperatures, and (3) urban effects on the formation of thermal signatures in the canopy layer.