Permanent and seasonally specific surface heat island structure in urban and non-urban areas in mid-latitude polycentric agglomeration based on Landsat images

The surface heat island (SHI), manifesting itself by increased surface temperatures in the city compared to the surrounding areas, is a dynamic phenomenon during the year. The study aims to recognise seasonal variability in the SHI structure (extent and composition of land cover type), and define an effective contribution and potential capability of particular land cover types for SHI development in a polycentric agglomeration based on LANDSAT satellite images. For the first time, the SHI structure was investigated separately in the urban and non-urban areas and the permanent and seasonally specific SHIs were delineated. Seasonal variability was a significant feature of SHI structure, particularly in its non-urban part, which was driven mainly by the vegetation annual cycle and altitude-dependent snow cover distribution in winter. In the majority of seasons, the intense urban SHI was conventionally compacted in the central most urbanized part of the metropolis, and its area was changing in a pulse-wise manner throughout the year from the maximum in summer to the minimum in autumn. The extent of permanent urban SHI indicating areas risky for human health was larger than the extent of seasonally specific urban SHIs. It covered 3% of GZM and was mostly composed of industrial and commercial units. Permanent non-urban SHI was scattered throughout the GZM without any clear pattern and covered only 0.4% of the entire GZM, and 75% of its area was covered by non-irrigated arable land and pastures. The identification of the surface types with permanent and seasonally variable ability to form SHI is helpful in planning urban spaces and adapting existing cities to contemporary climate changes.