Comparing heating and cooling effects of urban spatial structure factors on ambient air temperature: A quantitative synthesis using meta-analysis

Abstract

Numerous studies have examined how urban spatial structures influence ambient air temperature (AAT). However, the evidence on their effects and relative strength remains inconclusive and often conflicting due to varying analytical frameworks and spatiotemporal contexts. This meta-analysis quantitatively synthesizes the impacts of urban spatial structure factors from 34 peer-reviewed publications and draws comprehensive conclusions about their relationships. The analysis encompasses multidimensional factors of urban spatial structure related to land use and land cover (LULC), vegetation, building, and spatial layout. Seasonal and diurnal variations were further examined through subgroup analyses to explore heterogeneity. This study finally aims to compare the relative strength of multiple factors on AAT and discuss spatial planning strategies for urban heat mitigation. The results reveal that high building density and extensive impervious areas exert the strongest heating effects on AAT. Notably, layout-related factors, particularly height-to-width ratio and surface roughness, contribute to heating effects greater than intrinsic building properties, such as volume or height. Conversely, high normalized difference vegetation index (NDVI) and widespread tree areas emerge as the most effective cooling elements, with vegetative characteristics providing stronger cooling effects than natural-based LULC features. Seasonal and diurnal differences observed in several heating and cooling factors suggest that interactions between spatial elements and AAT vary under different meteorological conditions. Especially for urban heat mitigation in summer, expanding tree-based vegetation with improving NDVI is found to be more effective than reducing impervious areas and building density. These findings offer evidence-based guidance on which factors should be prioritized in climate-responsive urban planning.