SLUCM+BEM (v2.0): implementing a prognostic indoor temperature scheme for application to global cities

Abstract. We developed and released the single-layer urban canopy model (SLUCM) coupled with building energy model (BEM) v2.0, a single-layer urban canopy and building energy model capable of accurately simulating urban climates and electricity consumption (EC) across broad areas with substantially lower computational cost than conventional models. The previous version (v1.0) was a simplified model that set boundary conditions for wall and roof temperatures equal to the heating and air conditioning (HAC) setpoint. This prevented the calculation of indoor temperatures (T_in) under natural ventilation conditions (i.e. without HAC), limiting its applicability to wider regions and scenarios. This simplification was also identified as a key factor in the overestimation of EC in office districts of Tokyo. To address these issues, this study introduced a new version of the model in which T_in varies dynamically based on HAC usage, outdoor temperatures, and ventilation conditions. This enables T_in to be calculated during natural ventilation, and was shown to yield results consistent with observations from residential buildings in London under free-running conditions. Additionally, the overestimation of EC in office districts of Tokyo was significantly reduced. This upgrade facilitates the assessment of climate change adaptation measures for both outdoor and indoor environments. It enables an explicit simulation of the interactions between indoor and outdoor climates and human activities, including the consequent increase in outdoor temperatures due to anthropogenic heat emissions. The model is compatible with standard geographical datasets and existing WRF land-surface and urban physics options. SLUCM+BEM v2.0 is released both as an online WRF-coupled implementation and as a standalone version.