From expanding areas to stable areas: Identification, classification and determinants of multiple frequency urban heat islands

[Display omitted] •This paper focused on stable urban heat island which is lack of attention in current studies.•This paper used morphological spatial pattern analysis to identify the key zones.•This paper obtained the causes and characteristics of the stable urban heat island. People residing near stable urban heat islands (UHIs) experience a high long-term heat exposure, and the health consequences of such islands may be more severe than those of an expanding UHI; however, these areas are hidden in the overall heat island and not focused on. We developed a novel approach to identify the locations and ranges of stable UHIs by considering multiple frequency urban heat islands (MFUHIs). The MFUHIs were identified through multi-temporal remote sensing data and morphological spatial pattern analysis (MSPA), and the approach was applied in the case area of Beijing, the capital city of China. Specifically, the MFUHIs in Beijing were classified according to the landscape characteristics, based on the field survey and remote sensing data. The landscape indicators included land-use types, biophysical parameters (normalised difference vegetation index (NDVI), proportion of water areas, and impervious surface area (ISA)) and 3-D metrics (building density and building heights), which were considered causative factors. The relationship between the land surface temperature and landscape indicators was examined using ordinary least-squares (OLS) regressions and the Area Weighted Contribution Index (AWCI). The results showed that the MFUHIs in Beijing have four key zones, in which the surface temperature is more than 9 ℃ higher than the average temperature of the urban area, and the air temperature is 3.3–8.5 ℃ higher than the built-up temperature in the non-UHI area. The OLS regression and spatial statistics of the landscape indicators and surface temperature indicated that the regions in which area where MFUHIs occur could be characterised by a relatively high degree of impervious surface coverage, lack of green space and water area, and presence of low-rise and high-density buildings. The average number of building-floors in MFUHIs was between 1.93 and 2.64, and the number of floors in the entire study area was less than 3.6. Moreover, the building-densities in the MFUHIs were 16.25% to 27.62% higher than that in the whole study area. According to the result of the AWCI and field survey, the MFUHIs were classified into transportation, historical block, commercial, and