Vertical Thermal Stratification and Orientation Effects on Summer Outdoor Thermal Conditions of Campus Terraces in Severe Cold Regions

Optimizing outdoor thermal environments is essential for sustainable urban development and spatial resilience. Existing urban microclimate studies generally adopt the 1.5 m pedestrian height to represent outdoor thermal conditions. However, this widely accepted assumption has not been verified in multi-level campus spaces with terrace-induced complex three-dimensional environments, particularly in severe cold climate zones. This study investigates vertical thermal stratification and the relative influences of orientation, surface material, and height in Changchun, China. Field measurements at four levels were integrated with ENVI-met simulations calibrated against six independent validation sites. During summer peak hours, orientation dominates the thermal regime, outweighing both material and height. The peak thermal load shifts vertically from the south at lower elevations to the west at upper levels, generating a maximum air temperature difference of 1.66 °C compared to the consistently coolest east-facing terraces at 14:00. The vertical temperature profile does not follow a simple trend but varies with the surrounding geometry. Mid-level thermal trap appears near 3.5 m in the semi-enclosed building, where air temperature peaks before declining toward the roof. Moreover, an idealized model shows monotonic cooling with height, confirming that local obstructions cause the observed heat accumulation. During summer peak hours, surface material exerts a highly limited direct effect on ambient air temperature within these well-mixed three-dimensional spaces. Differences among concrete, asphalt, wood, and turf stay below 0.1 °C, roughly two orders of magnitude smaller than the orientation-driven contrast, because turbulent mixing and façade radiation overwhelm local surface heat fluxes. The findings highlight the inadequacy of evaluating thermal conditions at a single height, and challenge the conventional assumptions that material substitution is the primary heat mitigation measure in multi-level environments and that building orientation plays only a minor role in microclimate regulation. All quantitative outputs stem from ideal courtyard shapes and cloudless summer scenarios, reflecting mechanistic microclimate patterns instead of globally applicable predictive metrics. Local validation is mandatory before extending these conclusions to other seasons or building typologies. For sustainable summer thermal regulation on multi-level campuses, this work highlights orientation and adaptive shading as primary design measures, while material configuration acts only as auxiliary fine-tuning.