Impacts of residential block morphology and microclimate on operational carbon emissions: evidence from Xi'an, China

Residential blocks are fundamental spatial units of urban energy consumption and operational carbon emissions, and their spatial morphology influences energy use and carbon emission intensity through the regulation of local microclimate conditions. However, field-validated simulation-based evidence remains limited for understanding the coupled relationships among urban morphology, microclimate, and carbon emissions. In this study, a total of 127 residential blocks in Xi'an, China, were clustered, from which three major morphological types comprising 114 blocks were retained for typology-based analysis. Six typology-consistent blocks were selected for field microclimate measurements to support the validation of a multi-scale simulation framework integrating the Urban Weather Generator (UWG) with building energy modelling (URBANopt). Differences in microclimate and carbon emission responses among morphological block types were more pronounced in summer than in winter, and hourly analysis further revealed that carbon emission variations were more closely related to nighttime microclimate perturbations. Random forest analysis with SHAP interpretation showed that nighttime relative humidity changes made the largest statistical contribution to carbon emission variations. Among the ten selected morphological indicators, partial least squares regression identified building shape factor (BSF), mean building height (MBH), floor area ratio (FAR), and frontal area index (FAI) as the key variables associated with nighttime air temperature, with an explanatory power of R² = 0.854. Given the limited number of independently monitored residential blocks, the statistical findings should be interpreted as exploratory associations within the present dataset rather than as generalizable predictive relationships. With this scope, the findings provide case-specific evidence for developing and testing morphology-sensitive low-carbon renewal strategies.