Introducing the T-MCCR Index for Evaluating Urban Thermal Comfort and Morphological Performance

Urban morphology plays a key role in shaping outdoor thermal comfort, especially as cities experience increasing heat stress under climate change. While the Universal Thermal Climate Index (UTCI) is widely applied in outdoor thermal comfort studies, existing approaches rarely provide a comprehensive framework for evaluating and comparing the thermal comfort performance of urban morphologies across different times of the day. This study addresses this gap by proposing a time-aggregated, morphology-sensitive framework for comparative assessment of outdoor thermal comfort. Morphological performance is defined as the measurable capacity of an urban form to provide and sustain thermally comfortable outdoor conditions over time, emerging from the combined effects of its spatial configuration and geometry. Hourly UTCI simulations were conducted for three urban morphologies in Aachen, Germany, under present climate conditions and a high-emission future scenario (RCP 8.5, 2050). The urban fabric was discretized into uniform spatial parcels, and the proportion of thermally comfortable areas was evaluated across the diurnal cycle using the Time-weighted Morphological Climate Comfort Ratio (T-MCCR). The results show clear differences in thermal comfort performance among morphologies. Compact urban form exhibits higher comfort persistence and greater resilience under future climate conditions, whereas detached morphologies show lower performance and more fragmented comfort patterns. The proposed framework provides a comparative, design-support tool for morphology-driven thermal comfort evaluation.