Evaluation of the environmental impacts of urbanization from the viewpoint of increased skin temperatures: a case study from Istanbul, Turkey

Urbanization is an inevitable process all around the world especially in developing countries like Turkey. Istanbul has been experiencing rapid urban expansion for the past 60 years. This urban expansion is leading to the replacement of forests by various artificial surfaces. This situation has a critical impact on the natural surfaces due to the alteration of heat energy balance. In this study, the authors tried to investigate the extent of urbanization of Istanbul within the past decades to unearth its impacts on the urban heat island (UHI) severity and the level of its ecological consequences in terms of decreased thermal comfort. To this end, land use/cover (LULC) and land surface temperature (LST) maps were generated using Landsat imageries based on random forest (RF) classifier (as a machine learning tool) and radiometric image processing algorithms, respectively, for four different dates from 1989 to 2019. The statistical and spectral indicators were calculated for the study area to evaluate the association between urban development and UHI. Results indicate that Istanbul has suffered a continuous land transformation from forest to urban and croplands so that the area of forest has diminished by 373.3 km(2), and the artificial surfaces have increased by 260 km(2). Skin temperatures over all the LULC classes show an increase during the study period with the highest values estimated over artificial surfaces. The statistical analysis of urbanization indicators (ULI, PD, UGSI, NDVI, and NDBI) and UHI indicator (UTFVI) resulted in good correlation coefficients with the best agreement found between NDBI and UTFVI which stresses the strong link between the expansion of built-up areas as a result of urbanization and the severity of UHI and its ecological impacts in Istanbul. Thus, it is a must for policy-makers and officials of the city to take accurate measures regarding the urban planning to mitigate the harsh environmental impacts of growing urbanization of Istanbul in upcoming years.