The Effect of Urban Expansion on Urban Surface Temperature in Shenyang, China: an Analysis with Landsat Imagery

Landsat Thematic Mapper (TM)/Enhanced Thematic Mapper Plus (ETM+) images were used to assess the urban expansion dynamics and the corresponding thermal characteristics in Shenyang City, China. Unsupervised classification (ISODATA) and a hierarchy decision tree were applied to eight scenes of the Landsat images to derive the land use/land cover (LULC) around the Shenyang metropolitan region from 1986 to 2007. Landsat TM/ETM+ thermal infrared (TIR) images (band 6) were used to investigate the urban surface thermal patterns by retrieving land surface temperature (LST) using a mono-window algorithm. Results reveal that the built-up area has doubled from 1986 (20.2 %) to 2007 (42.3 %), most of which is converted from croplands around the urban fringe area. The built-up area has close association with the population increase (R² = 0.89), the gross domestic production (R² = 0.94), and fixed asset investments (R² = 0.95). These illustrate the contributions of socioeconomic factors to the rapid urban expansion in Shenyang. Three urban heat island (UHI) indices [i.e., heat effect contribution index (H ᵢ), weighted heat unit index (D₁), and regional weighted heat unit index (D₂)] were used to characterize the urban thermal patterns for removing the phenological effects and to confirm the linkage between UHI and urban expansion. Results show that urban areas have an obvious daytime heating effect (heat source) that is strongly correlated with urban expansion, wherein a higher percentage of an impervious surface is usually associated with a higher surface temperature. Further analyses indicate that urban expansion is fairly correlated to H ᵢ ' (R² = 0.63) but strongly to D₂(R² = 0.91). Additional research is needed to further quantify the inner urban area to gain a better understanding of UHI resulting from various heat fluxes and urban components.