The Effects of Biophysical Compounds on Urban Heat Islands Formation (Case Study: Mashhad)

Urban heat island (UHI) phenomenon has been intensified due to the effects of climate change and urbanization in recent years. Spatial-temporal patterns of biophysical composition consisting of vegetation, impervious surface, and soil type affect the UHI significantly. The main aim of this study is to investigate the effects of biophysical parameters on formation and clustering of heat island in the city of Mashhad. In order to achieve the aim, images of OLI and TIRS sensors of Landsat 8 were used for the month of August in years 2013, 2014, and 2015. An object-oriented innovative approach was used to extract UHI values using land surface temperature (LST) data. Clusters of hot and cold heat islands were extracted by local index spatial autocorrelation (LISA) method. Moreover, to evaluate composition of biophysical in Mashhad, three indices including NDVI, NDBI of NDBal were used. Correlation analysis between biophysical parameters showed that by increasing the value of LST, spatial heterogeneity of the cluster increased due to non-linear pattern. The results also detected three types of UHI: peripheral heat islands, focal heat islands, and the linear heat islands. Spatial autocorrelation analysis using Gary and Moran indices show a decrease value indicating loss of spatial order in LST. According to spatial correlation analysis of Moran's local, the size of hot heat islands has been increased during the study period in the city of Mashhad.