The Impact of Urban Use on Creation of Thermal Islands (Case Study: Mashhad City)

With the development of urbanization, large amounts of agricultural and forest areas are replaced with houses, industrial areas and other infrastructure. The warming of the urban environment is one of the unintentional impacts of unsustainable urban development, which is called the "urban thermal island." In this research, the thermal islands of Mashhad, one of the most important populated tourist centers of Iran that has had a rapid development during the last few decades has been studied. Using OLI and TIRS data from Landsat 8 and a two-window algorithm based on the amount of ground temperature and the amount of vegetation cover, which is calculated based on vegetation cover index of ground level [1] and vegetation cover on the earth's surface, the thermal level map of Mashhad city was calculated. The results showed that there is a relationship between vegetation index and surface temperature of the earth, which helps us to predict the surface temperature. Using vegetation index and separate window algorithm, it is found that the area 6 has the highest temperature and the lowest green space, and region 12 has the lowest temperature and the highest green space (vegetation). In this research, we tried to use a satellite image processing method to determine the surface temperature of the areas in the comprehensive plan of Mashhad. For this purpose, after performing the preprocessing on the image and the necessary corrections to determine the type of usage, the supervised classification method and the maximum probability algorithm were used. In this classification method each pixel is assigned to a class that has the most probability of belonging to that class (Fatemi & Rezaee, 2010). In fact, in this method, the variance and covariance of classes are used and each pixel of the image is assigned to the class that most closely resembles it (Alavi Panah, 2002).
The images used in this research are related to Landsat 8 and TRS sensors (bands 10 and 11) and OLI (bands 1 through 9) on 2017.6.6 (1396.3.6). The ground surface temperature was calculated based on the two-window algorithm method. The two-window algorithm calculates the surface temperature of the earth based on the Land Surface Earth (LSE) and Fractional Vegetation Cover (FVC). The results of this study indicate that the surface temperature of the earth is affected by the use of different land surface areas. Also, the results show that by establishing a relationship between the vegetation index such as NDVI and FVC, we can predict ground temperatures to obtain better results. With regard to surface temperature estimation, it is possible to use high-bandwidth resolution image sensors (Feizizadeh & Dedehban, 2015). Accordingly, the use of a separate window algorithm due to the use of 2 thermal bands is more accurate than the single-window method. In addition to thermal bands, other criteria also affect this algorithm which is based on mathematical relations. As previous studies have indicated, surface temperatures are higher in areas with less vegetation (Feizizadeh.B, Blaschke.T, Nazmfar,H ,Akbari,E and Kohbanani,H,R, 2012) as well as asphalt beds and roofing coatings with a darker color than those of bright colors (green roofs). In summary the results of this research can be summarized as follows:In the study of the relationship between land use land surface temperature and vegetation, it was determined that the use of green space at 11 ° C and the use of water at 8 ° C had the lowest surface temperature and residential use at 21 ° C and asphalt coating at 23 ° C Maximum surface temperature. Asphalt pavement agent has a great influence on the creation of thermal islands. The northern parts of Mashhad, the airport, and highways where the amount of asphalt used is high has a higher temperature.
Area 6 has the highest temperature and the lowest green space indicating a high density housing area without vegetation and area 12 has the lowest temperature and most green space. By moving from downtown to the foothills around Mashhad factors such as wind and vegetation can lead to lower temperature.
The most prominent urban green spaces of Mellat Park are in area 9 and Kouh Sangi in area 8, and due to the remoteness of these green spaces from the industrial areas and the vast areas of Mashhad, the surface temperature is very low.
In area 9 of Mashhad (Ab o Bargh Mountains) and the green belt around Mashhad, there is a part of the vegetation of the pastures and grasslands which include a natural vegetation and are better restored by the enclosure and prevented from degradation.