Spatial development indicators as a tool to determine thermal conditions in an urban environment.

• Open source data and a dense in-situ air temperature measurement network were used. • The ratio of biologically vital areas impacts city thermal conditions the most. • Build-up indicators with vertical features present thermal regime better than others. • The area of radius of at least 100 m is the best for evaluating thermal conditions. • Spatial development particularly influences minimum and average air temperature. In the face of climate change and the growing frequency of thermally burdensome conditions, urban morphology and city planning are becoming increasingly important to human health. Architects and policymakers use various tools, including spatial development indicators describing the characteristics of built-up areas, to mitigate urban climate. This study purposed to (1) indicate which widely used spatial development indicators most adequately explained the thermal conditions of the environment, and (2) investigate how large an area most accurately represents the thermal features recorded at a given air temperature measurement site. Selected indexes were used to characterize each of the 21 measuring sites located in Warsaw. First, five spatial development indicators were calculated for three distances from each site. Then, based on data from the air temperature monitoring network, 17 selected thermal characteristics were calculated. The results of the analyses indicated that the Ratio of Biologically Vital Area has the highest impact on the thermal regime with particularly strong influence on the lowest daily temperature values. The paper proves that the thermal conditions of a given location in the diverse space of a city are more precisely represented by a large area than by its nearest surroundings. [Display omitted] [ABSTRACT FROM AUTHOR]