Analysis and Evaluation of the Formation of a Heat Island in Tehran During Three Decades

The rising temperature of the earth's surface and the formation of heat islands in megacities have become two of the biggest environmental threats. This compound problem affects urban climatology, including urban vegetation and air pollution, human health, and the environment, including the group of vulnerable members of the society and public health, leading to the growing death rate. Hence, the purpose of this study is to investigate the leading causes of temperature changes and the development of a thermal island in the city of Tehran following the expansion of this metropolis in recent decades. This research uses thermal remote sensing and GIS techniques to analyze information from Landsat satellite images in (TM-ETM-TIRS) sensors from 1984 to 2020. The results of the research indicated that the surface temperature of the city of Tehran during the years 1984 to 1996, 1998 to 2008, and 2010 to 2020 experienced a relative increase in the summer and winter seasons. In the first decade, the average temperature of the green layer was -7, while the temperature of the magenta and red layers were 20 and 25 degrees, respectively. In the second decade, the average temperatures of the green and dark green classes were -1 and 3 while they were 23 and 27 degrees for the magenta and red classes, respectively. In the third decade, the average temperatures of the green and dark green classes were -1 and 3, and thost of the magenta and red layers increased to 28 and 31 degrees, respectively. Furthermore, the analysis of vegetation cover based on the NDVI index pointed to the continuing reduction of vegetation in the studied years. Regarding the direct correlation between the heat island and vegetation and the concentration of the heat island in the city center, further measures must be taken and the vegetation cover should be increased to reduce the heat island. The city center needs to be decentralized as part of the remedy via proper urban design and planning.