Investigation of the vegetation index changes in the formation of the urban heat islands (Case study: Urmia city)

Nowadays, many factors such as destruction of the urban green areas and increasing the environmental pollutants in urban areas cause the solar radiation confinement and formation of urban heat island phenomenon. This has dangerous consequences, such as stagnation and lack of the air flow, transmission of air pollution and dispersed toxic particles in urban areas. The main purpose of this research is to analyze the vegetation status and land surface temperature in Urmia city, investigate the formation of urban heat islands and analyze their temporal and spatial variations. For achieving these purposes, Landsat 4 and 8 satellite images for 1989 and 2017 years were used. In this study, after applying the necessary corrections to the images and training them, land use change detection  was accomplished. By using the red and the near infrared bands of the images, the vegetation index (NDVI) was calculated and then. Ground surface temperature (LST) was calculated by the image thermal bands. The results of this research showed that the temperature of Urmia city and its suburbs increased during the 28 years (1989-2017). It was also found that increasing temperatures within Urmia city was mainly due to the loss of the vegetation areas and to the conversion of the green area to urban lands by urbanization processes. The results showed that the vegetation index (NDVI) in Urmia city decreased as it reashed to-0.053 from 0.023 in the wasteland, which indicate the disappearance of thin green cover (about 9.24% of the vegetation cover of Urmia city disappeared during 1989–2017).