This paper presents a methodology to approximate the urban heat island effect by using a PostgreSQL database and CitySim software, a simulation tool to evaluate urban energy flows. A ground temperature model has been developed for shallow depths (until 4m), which reproduces the phenomena of heat transfer into the ground on an hourly basis. This model is further used to predict the outdoor ground surface temperature, which is an indicator of the urban heat island effect. A PostgreSQL database which contains information such as the building footprints, geographical location, address, construction date, energy system etc. of the buildings was modified to include data relative to this model. A case study has been performed in a small neighbourhood, Rue des Maraîchers, in Geneva (Switzerland) in order to illustrate the usage of this tool to analyse the surface temperature of asphalted roads and green alleys. Finally, a methodology has been introduced to predict the urban heat island effect using this temperature.