Document Type : Research Paper
Associated Professor. of Geography and Urban Planning, University of Tabriz
MSc. Remote Sensing and Geographic Information Systems,, University of Tabriz
The thermal island phenomenon is the excess heat on the surface of the earth and the atmosphere of urban areas compared to its suburbs. Thermal island by changing the pattern of local winds, enhancing the growth of clouds and fog, increasing lightning and affecting rainfall, lowers the urban air and causes discomfort and discomfort to city dwellers and by affecting human health, the possibility of asthma and various diseases Increases other respiration. Therefore, this research has been done with the nature of developmental-applied and descriptive-analytical and the purpose of simulation and calculation of the maximum intensity of urban heat islands (UHImax) according to urban geometry conditions in Valiasr and Shanb Ghazan alleys of Tabriz.
The present research is descriptive-analytical in terms of method and has a developmental-applied nature. In this study, the required data were obtained through library, documentary and field studies. In this research, Landsat satellite imagery of 8 OLI and TIRS sensors in 163 and row 34 for the years 13/01/2019 and 12/08/2019 has been used. The method of this research is based on Oke numerical-theoretical equation. To do this, first the geometry of the desired areas according to a radius of 20 meters in Valiasr alley and 15 meters in the Ghazan slope from the axis of the passages to separate blocks and then the ratio of width of the passages and height of the building (H / W) in GIS software Finally, based on Oke equation, UHImax was calculated and simulated.
In this study, in order to calculate the height-width ratio (H / W), first using ARCGIS10.5 software, the central axis of the passages was determined and then to determine the average height of buildings effective in thermal island changes, a radius of 20 meters left and right of the passages for Valiasr alley and a radius of 15 meters was considered for Shanb Ghazan area (the choice of radii depended on the width of the passages). After selecting the appropriate radius for both areas, the blocks were extracted and separated. According to the number of building floors (1 to 5) for Shanb Ghazan area and (1 to 11) for Valiasr alley and the average height of each block, the amount of homogeneity or heterogeneity of each block was determined. According to the passages, the blocks of the studied areas were divided into 10 different blocks from A to J. After selecting the appropriate radius of the building block in each axis, the height of the buildings was classified into three categories: low, medium and high. Then, using the H / W ratio, the intensity of the thermal island in each block was calculated. Also, in order to estimate the effect of the width of the passages and the height of the building on the changes in the intensity of the thermal island of Tabriz, a multiple regression model was used. Finally, after calculating the intensity of the thermal island in Valiasr and Shanb Ghazan alleys, the intensity of the thermal islands in both regions were compared and compared with the Earth surface temperature (LST) map obtained from the Landsat 8 satellite TIRS sensor.
The results showed that the increase in population and construction in Tabriz metropolis has caused an increase in temperature. The results obtained from both areas showed that the physical and geometric conditions of Tabriz have a great impact on increasing the thermal island of the city, so that the taller the buildings and the smaller the width of the passages, the intensity of the thermal island The more and vice versa, the lower the intensity of the thermal island. As the width of the passages decreases, the pattern of local winds changes and they can rarely circulate freely in the passages, directing the heat out of the environment and adjusting the temperature there. Narrow passages absorb heat during the day and keep it in the urban environment for hours after sunset. These narrow passages, like deep and narrow valleys, reduce the long wavelength of radiation from the narrow width of the street and keep the heat at the surface of the passages, which increases the intensity of the thermal island. As the results showed, in Valiasr alley, among 10 blocks, block D with 1.9 degrees and block H with 8.2 degrees Celsius has the lowest and highest values of thermal island intensity. In Shanb Ghazan region, among the blocks, block G with 0.8 degrees has the lowest and block B with 6.8 degrees has the highest heat island intensity. Therefore, it can be acknowledged that according to the width of the passages and the height of the buildings in Valiasr alley and Shanb Ghazan area, blocks D and G have the most standard configuration and blocks H and B have the most standard configuration in these areas. The final results showed that although the height of the building has a significant role in increasing the intensity of the thermal island, but based on the estimation of the multivariate regression model, the effect of the width of the passages in Valiasr alley with 0.91 is much greater than the height of the building with 0.6 and Shanb Ghazan area with 0.92 much more than the height of the building with 0.5 is involved in changes in the intensity of the thermal island. Also, the comparison of the variables of width of passages and height of buildings in the studied areas showed that the width of passages in Valiasr alley had the least effect compared to Shanb Ghazan area and the height of buildings was the opposite. The results of surface temperature in the study areas also showed that Valiasr alley has the highest and lowest temperatures in winter and summer, respectively, while the surface temperature in both winter and summer in Shanb Ghazan region did not differ much. And the surface temperature in this area is low.