Microclimatic impacts of building projects on the local neighborhood: criteria for well-founded urban planning

• Microclimatic impact of urban development projects on the surrounding area • Catalogue of criteria for the need for microclimate analyses at neighborhood level • Sensitivity experiments with the urban climate model PALM • Idealized building projects based on the Local Climate Zone concept • Urban development can affect the air temperature in the surroundings City administration is struggling with steering urban development into a climate resilient direction and needs supportive guidelines for informed decision-making. The results of this research present a planning criteria catalogue to identify microclimate-sensitive development projects to the surrounding area. It provides selected parameters and thresholds characterizing construction projects to request spatially extended microclimatic evaluations based on changes of expected spatial extension and intensity of 2 m air temperature in the surrounding area. To quantify the impact of project characteristics on this evaluation metric in the neighborhood, 50 experiments were conducted for inner-city and periphery domains using the urban climate model PALM with varying static input parameters including area size, building height, and Local Climate Zone (LCZ) classifications representing different building densities and soil sealing patterns. The resulting impacts are evaluated in a distance of 50-100 meters from construction sites. Development projects in an LCZ compact style, showed air temperature increases of up to 1.5°C during evening hours in an inner-city domain. LCZ open configurations caused slightly higher temperatures during the night and morning hours of up to 0.7°C. For a periphery domain, LCZ open did not show any notable impact on the surroundings, while LCZ large low-rise caused persistent temperature increases peaking at 1.5°C in evening hours. Based on these findings, a practical catalogue of criteria was developed to guide authorities in determining when spatially extended microclimate analyses (including the potentially affected neighborhood) should be required or recommended. The study suggests extended assessments when air temperature changes exceed 1°C in surrounding areas during any time during the day, which is particularly the case for compact and large low-rise built environments. This quantitative framework guides authorities to decide in which cases a climate simulation is recommended or required for the assessment of projects with potential significant microclimatic impacts on neighborhoods.