Document Type : Original Article
Department of Urban Engineering, University of Guilan, Rasht, Iran
Department of Climatology, Sayyed Jamaleddin Asadabadi University, Asadabad,, Iran
Department of Urban Climatology, University of Isfahan,, Isfahan, Iran
Department of Remote Sensing, University of Khavaran, Mashhad, Iran
In recent decades, along with the physical development of cities and population increase due to immigration, Heat islands, which are mainly the result of human made activities, have gained significant importance. So that; The reduction of vegetation cover, the high consumption of fossil fuels, the emission of greenhouse gases and the use of inappropriate materials in urban construction have created the microclimate of a heat island above the metropolis of the world. Finally, it causes an increase in the land surface temperature, atmospheric stability, persistence and stabilization of pollutants and an increase in respiratory diseases. Today, by using remote sensing methods and using digital satellite images, it is possible to examine the land surface temperature with high accuracy and in a short period using MODIS sensor and Terra satellite images. Therefore, the main objective of the current research is to analyze the temporal and spatial variations of heat islands of Isfahan using the principal component analysis method. With this technique, it is possible to identify the seasons and months when increased the land surface temperature and the heat island.
Materials and methods
In this regard, the present research considers analyzing the temporal and spatial variations of this phenomenon in Isfahan during period of 20 years (from 2000 to 2020 AD). To achieve this purpose, was used the land surface temperature (LST) data extracted by MODIS sensor and Terra satellite. These data are available for the whole world with a time resolution of 8 days and a spatial resolution of 1x1 km in a sinusoidal grid with dimensions of 1200x1200 km. Therefore, for Isfahan, 913 images extracted from the MODIS sensor. Then, with the principal component analysis (PCA) method, the seasons and months that have the most influence on the occurrence of heat islands identified and in order to analyze the trend of this phenomenon, were used the Mann-Kendall test and the Kolmogorov-Smirnov test.
Results and discussion
The findings of the research indicate that, the land surface temperature in the last 20 years in Isfahan had an increasing trend with rate of 4%. Although this trend in the population and urban centers has been completely different from the surrounding areas of Isfahan. In terms of spatial distribution, the highest occurrence of heat island in the eastern and southeastern parts (including Hassan Abad and Jolgeh) due to its proximity to the hot deserts of Kavir-Lout, proximity to Sepiddasht, Varzaneh, Shahrak Ramsheh industrial towns and changing in the land use of agricultural to industrial and residential has been registered. also in the North-West region (including Mahmudabad and Isfahan city) due to the increase in man-made heating caused by the increase in the consumption of fossil fuels, the growth of residential, industrial and commercial units, temperature has risen. In addition, the results showed that the intensity of the heat island in winter is more than in summer, and the most intense time of its occurrence recorded in January and the least in November.
Isfahan is integrally affect by global climate conditions, but depending on the geographical location of each part of this province, the land surface temperature and the occurrence of heat islands are different, so that, eastern and central parts, adjacent to Kavir-Lout and close to industrial towns, have an increasing trend. Moreover, the southern parts have a decreasing rate of temperature and heat islands due to less urban population, larger agricultural lands and more vegetation. The increase in urbanization, migration, and the increase in fossil fuel consumption, the decrease in vegetation, the aggravation of drought, and the change of land use have a fundamental role in increasing the occurrence of this phenomenon.