High-Resolution UAV-Derived Urban Radiation Environment Mapping Through Mean Radiant Temperature Simulation Using SOLWEIG

Abstract

Urban areas are increasingly exposed to extreme heat conditions due to rapid urbanization, climate change, and the intensification of the Urban Heat Island (UHI) effect. Accurate characterization of the urban radiation environment is therefore essential for supporting climate-responsive urban planning and sustainable landscape design. This study presents a high-resolution microscale assessment of the spatial and temporal distribution of mean radiant temperature (Tmrt) in a representative urban district of Bal & ccedil;ova, & Idot;zmir, T & uuml;rkiye, using unmanned aerial vehicle (UAV)-derived spatial data and the Solar and LongWave Environmental Irradiance Geometry (SOLWEIG) model implemented within the Urban Multi-scale Environmental Predictor (UMEP) framework in QGIS. High-resolution Digital Surface Models (DSM) and Digital Elevation Models (DEM) were generated from UAV photogrammetry and integrated with hourly meteorological observations, including air temperature, relative humidity, and wind speed, obtained from the Turkish State Meteorological Service for 10 June 2023 Hourly meteorological observations corresponding to 10 June 2023 were obtained from the Turkish State Meteorological Service (TSMS). The SOLWEIG model was employed to simulate hourly mean radiant temperature, shadow distribution, wall characteristics, and sky view factor (SVF), enabling detailed evaluation of radiation exposure across a microscale urban environment. The simulation results demonstrate substantial spatial variability in mean radiant temperature associated with urban morphology. Areas characterized by taller buildings, greater shading intensity, and reduced sky exposure consistently exhibited lower Tmrt values throughout the daytime, whereas open paved surfaces with high sky visibility experienced considerably greater radiative heat loads. The generated shadow and SVF maps further reveal the dominant influence of building geometry and vegetation on modifying local radiation conditions. Rather than directly evaluating human thermal comfort indices such as Physiological Equivalent Temperature (PET) or Universal Thermal Climate Index (UTCI), this research focuses specifically on the radiative component governing outdoor thermal environments through high-resolution Tmrt modelling. The findings demonstrate that integrating UAV-derived three-dimensional urban morphology with physically based radiation modelling provides an effective framework for identifying localized heat exposure patterns and supporting evidence-based urban climate adaptation strategies. The proposed methodology offers a practical, open-source, and transferable workflow for microscale urban radiation assessment in climate-sensitive cities while providing valuable spatial information for future thermal comfort analyses and urban design applications.