Spatial analysis and trend extraction of urban heat islands in Iran's major cities in the summer season

The effect of the urban environment on the atmospheric air and the boundary layer of urban areas appears mostly in the form of a temperature island. The urban heat island creates an artificial thermal environment due to the significant disturbance of energy, heat and radiative forcings, which have faced challenges for urban residents, water resources, urban infrastructure, atmospheric pollutants and social comfort. In addition, it aggravates the heat and has a negative effect on life expectancy. The purpose of this research is to analyze the spatial and process of urban heat islands of Iranian metropolises in the summer season.

In this research,, five big cities of Iran including Tehran, Mashhad, Isfahan, Shiraz and Karaj were selected. Then, Landsat 7 and 8 satellite images from 2003 to 2018 were used to recover the land surface temperature (LST) and for spatial analysis we used the Gates-Ord-J statistics. Finally, for trend analysis, the Mann-Kendall method was used.

The results showed that the average LST in the built-up areas within the city limits is higher than the average LST in the surrounding non-urban areas and even sometimes the city itself, and the strongest (SUHI) has occurred in areas such as the asphalt surfaces of airport runways, parking lots and roofs. The intensity (SHUI) in all metropolitan cities in the city center was not higher than other areas. The results of trend analysis using Kendall's method showed that the surface temperature of the earth is increasing in all the five cities of Iran except for Isfahan. Also, regarding the spatial distribution of the surface temperature in the five cities of Iran, it was found that there is an inverse relationship between the building density and the surface temperature.

The surface temperature of the earth was increasing in all studied cities. The slope of the trend was also higher than 1 degree Celsius for the major cities under study, and the intensity of the trend was higher in Karaj city than other major cities under study. The minimum slope of the earth surface temperature trend was calculated in Isfahan and the maximum slope was calculated in Karaj. In the next studies, it is suggested to study more cities in order to make better plans for the development of other cities.