Understanding heat exposure through morphological descriptors of intra-urban heterogeneity

Thermal variability in urban environments significantly influences heat exposure patterns and the selection of climate adaptation measures. Different morphological descriptors are widely used in urban climate studies, however their application in capturing intra-urban heterogeneity and explaining different levels of heat exposure at the microscale remains underexplored. While new forms of urbanisation are arising through re-development and in-fill processes, existing studies often employ a fragmented approach, either by selecting a limited number of descriptors without comprehensive explanation, by using aggregative descriptors assuming conditions of homogeneity in an area, or by failing to assess whether these descriptors capture the existing form differences. As a result, interventions based on these assumptions may lead to an unequal distribution, ultimately affecting human health.This study addresses these gaps by conducting a systematic literature review to identify, categorise, and critically evaluate morphological descriptors in urban climate research. The research objectives are threefold: (1) to systematically review and categorise morphological descriptors based on their ability to describe intra-urban heterogeneity, particularly related to urban heat exposure; (2) to examine how these descriptors were applied in previous studies, considering different spatial scales; and (3) to assess the correlations between morphological descriptors and thermal variability, validating their relevance in explaining heat exposure. This evaluation considers factors such as spatial aggregation, sensitivity analysis across previous case studies, and the scale dependency of form-climate relationships.The study aims to meet these objectives by synthesizing findings from the literature and by identifying descriptors with strong (positive or negative) correlations to heat exposure, to explain thermal variability. The results contribute to expanding knowledge for developing climate methods to better describe contemporary complex urbanisations, informing the development of more accurate climate-based classification approaches. Ultimately, this work supports climate-adaptive urban planning by offering a structured approach to selecting and applying morphological descriptors for heat exposure analysis.