Abstract
The urban heat island (UHI) effect resulting from rapid urbanization generally has a negative impact on urban residents. Shijiazhuang, the capital of Hebei Province in China, was selected to assess surface thermal patterns and its correlation with Land Cover Types (LCTs). This study was conducted using Landsat TM images on the mesoscale level and airborne hyperspectral thermal images on the microscale level. Land surface temperature (LST) was retrieved from four scenes of Landsat TM data in the summer days to analyze the thermal spatial patterns and intensity of surface UHI (SUHI). Surface thermal characteristics were further examined by relating LST to percentage of imperious surface area (ISA%) and four remote sensing indices (RSIs), the Normalized Difference Vegetation Index (NDVI), Universal Pattern Decomposition method (VIUPD), Normalized Difference Built-up Index (NDBI) and Biophysical Composition Index (BCI). On the other hand, fives scenes of airborne TASI (Thermal Airborne Spectrographic Imager sensor) images were utilized to describe more detailed urban thermal characteristics of the downtown of Shijiazhuang city. Our results show that an obvious surface heat island effect existed in the study area during summer days, with a SUHI intensity of 2–4 °C. The analyses reveal that ISA% can provide an additional metric for the study of SUHI, yet its association with LST is not straightforward and this should a focus in future work. It was also found that two physically based indices, VIUPD and BCI, have the potential to account for the variation in urban LST. The results concerning on TASI indicate that diversity of impervious surfaces (rooftops, concrete, and mixed asphalt) contribute most to the SUHI, among all of the land cover features. Moreover, the effect of impervious surfaces on LST is complicated, and the composition and arrangement of land cover features may play an important role in determining the magnitude and intensity of SUHI. Overall, the analysis of urban thermal signatures at two spatial scales complement each other and the use of airborne imagery data with higher spatial resolution is helpful in revealing more details for understanding urban thermal environments.
Highlights
Land Cover Types (LCTs) have played a significant role in environmental change, and accurate and real-time information of LCTs is critical to environmental monitoring and management [1,2]
We found that a considerable fraction of the short grassland was interspersed with urban wetland, which would contribute to the lower Land surface temperature (LST)
Through the inspections of the correlations of remote sensing indices (RSIs), impervious surface area (ISA)% and LST, we found that the increase of vegetation cover would decrease LST; whereas the increase of impervious surfaces would increase LST as well as facilitating the urban heat island phenomena
Summary
LCTs have played a significant role in environmental change, and accurate and real-time information of LCTs is critical to environmental monitoring and management [1,2]. The interaction between LCTs and climatic variability is so complex that advanced models are required to describe this process, especially for urban–rural areas. Since the change from nature areas to impervious areas can result in significant regional climate changes, urban thermal environments have been identified in some studies from the perspective of the scientific community for meteorology and remote sensing [3,4,5]. The differences in surface temperature between urban areas and surrounding rural areas, a phenomenon termed as urban heat island (UHI) effect and due to urbanization, have been widely observed [6,7]. UHI considerably increases the energy demands and degrades the outdoor air quality especially in summertime, as accompanying the negative impact on the local mseteorology conditions. The utilization of remote sensing in the assessment of surface thermal properties as well as surface
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