Heat exposure variations and mitigation in a densely populated neighborhood during a hot day: Towards a people-oriented approach to urban climate management

Climate change and increasing urbanization call for the effective adaptation of cities to extreme heat. To improve the applicability of the research, sophisticated computational fluid dynamics models are being developed to capture the complexity of climate in a real urban environment, while a human-oriented paradigm is emerging concurrently. In this paper we present a synergy of these approaches by analyzing outdoor thermal exposure on five different pedestrian routes in Prague-Dejvice (Czech Republic), employing the PALM modeling system and realistic use-cases. Our simulations reveal important spatio-temporal variability in the Universal Thermal Climate Index (UTCI) in the urban neighborhood. Our findings particularly emphasize the negative effect of open spaces, such as gaps between buildings and shorter buildings, on the thermal exposure of pedestrians. These configurations allow more direct irradiation to reach ground level, while the other adverse climatic characteristics of midrise/highrise developments are largely preserved. The effect of urban greenery is quite variable during the day. Trees can reduce UTCI by up to 10 degrees C, but this strongly depends on the location (e.g., distance from neighboring buildings). Irrigated grass reduces UTCI by about 1.8 degrees C, but dried grass has little heat mitigation effect. In conclusion, our results suggest that expert-based knowledge together with sophisticated and fine-scale models can identify effective heat stress reduction measures without draconian changes to, or investments in, the urban environment.