The Structural Limits of Cooling: (Fragmentation and Shape Inefficiency Constrain Green Infrastructure in an Arid Urban Heat Island).

The mitigation of the Urban Heat Island (UHI) effect necessitates a comprehensive understanding of how the spatial configuration of Green Infrastructure (GI) influences its thermal performance. Traditional metrics often fail to capture this functional relationship. This study addresses this gap by integrating the Green Space Thermal Effectiveness Index (GSTEI) with landscape ecology metrics to analyze GI in the rapidly urbanizing City of Qom, Iran. Using Landsat 9 Land Surface Temperature (LST) and Sentinel-2 NDVI data from the summer of 2023, the continuous GSTEI (net cooling in ∘C) was calculated and reclassified into four discrete thermal performance classes (Low: 0 − 2∘C to Very High: > 10∘C). The FRAGSTATS analysis revealed that the overall urban GI landscape is highly fragmented, characterized by a high Edge Density (ED = 78.51 m/ha) and low patch dominance (LPI = 2.51%). Critically, thermal performance was found to be strongly configuration-dependent: the least effective GI (Low cooling class) exhibited the highest fragmentation (Patch Density = 243.21 per ha) and the lowest aggregation (Clumpiness = 0.5664). Conversely, higher-performing classes were significantly more clumped, demonstrating the thermal benefits of spatial consolidation. Paradoxically, the Very High cooling class (> 10 °C) was characterized by the smallest mean patch size (0.084 ha), suggesting that intensive, high-density vegetation can occasionally bypass the structural constraints of small area. Adjacency analysis further confirmed a strict thermal flow gradient, where low-performing patches had the highest interface with the heat-emitting built-up matrix. These findings confirm that fragmentation significantly compromises the cooling function of urban green space. The study provides a quantifiable framework for planners, emphasizing that while consolidation of fragmented patches is generally essential for UHI mitigation, small patches can achieve exceptional cooling through high-density design, offering a dual strategy for arid urban environments.