Identifying the trend of spatial and temporal changes of heat islands in metropolises using MODIS sensor images (case study of Mashhad, Tehran, Ahvaz, Tabriz, Isfahan metropolises)

Dissertation for M.Sc

Remote Sensing and Geographical Information System - Water and Soil Resources

Abstract: Urban heat islands are areas of the earth's surface that have a higher temperature than neighboring areas. The spread of this phenomenon varies in space and time. The creation of thermal islands and its spatial and temporal changes are mostly influenced by changes in land cover and heat emission resulting from human activities. Considering the high changes per unit of time and the continuity and spatial expansion of this phenomenon, remote sensing is one of the appropriate tools to study this phenomenon. The purpose of this research is to study the expansion of thermal islands and the relationship between surface temperature and land cover in the metropolises of Ahvaz, Isfahan, Tabriz, Tehran, and Mashhad, as the most important population and industrial centers of Iran. To reach the above goal, the expansion of thermal islands in the period from 2007 to 2011 and also the relationship between surface temperature and surface cover have been investigated using MODIS sensors in the aforementioned cities. For this purpose, by applying clustering on MOD11A2 thermal products of MODIS sensor, the spread of thermal islands was investigated and by extracting land cover from ETM+ images, the relationship between surface cover changes and land surface temperature was investigated. The effect of different covers on the surface temperature with separate fitting as well as the combined fitting of the covers with the ground surface temperature as well as using the products of MOD13A2 vegetation indicators have been investigated by the developed regression model. The results show that over time, thermal islands have expanded and in some cases, new thermal islands have been created. In the studied period, Mashhad and Ahvaz had the highest expansion of thermal islands with 77 and 74% expansion compared to the initial core of the islands in 2007, followed by Tehran, Tabriz and Isfahan with 54, 53 and 33% expansion compared to the initial core of the islands in 2007 respectively. The regression model developed to estimate the surface temperature in these cities indicated the severe effect of the reduction of vegetation cover in cities located in hot climates. Due to the heterogeneity of built surfaces (residential, industrial areas, airports, etc.), these surfaces show a positive relationship in some cases (Ahvaz, Isfahan and Tehran) and a negative relationship in some cases (Mashhad and Tabriz) with the surface temperature of the earth. The use of accurate coverage and use information is necessary to specify their role in future studies.

Keywords: urban heat island, spatial and temporal changes of heat islands, land cover, MODIS gauge

1- Chapter 1: General research

1-1- Introduction:

With the development of urbanization, large amounts of agricultural and forest areas have been replaced by urban areas. Modern urban areas are covered by asphalt, concrete and other impervious surfaces. Urban growth, especially in big cities, leads to land cover changes at a high speed. Since the temperature of the earth's surface in any area depends on the characteristics of the materials that make up the surface and the reflection of the sun's energy, the thermal pattern of urban areas is significantly different from non-urban areas. The high heat capacity of materials used in cities, the reduction of albedo and the presence of heat sources caused by human activities cause the temperature of some urban areas to increase compared to other areas and changes in the heat balance of these areas. Therefore, in urban areas, depending on the existing covers and uses, areas with higher temperatures than other areas arise, this phenomenon is named as the heat island of cities [1].

In addition to the fact that this increase in temperature in turn has a significant effect on atmospheric, biological and economic conditions, estimating the surface temperature in different urban areas in order to investigate the temperature distribution of the earth's surface and the causes of its occurrence has many applications, such as determining the role of traffic and industrial settlements in warming cities. Therefore, investigating and analyzing the phenomenon of heat islands in cities is very important.

Remote sensing images, due to their wide coverage, timeliness and the ability to obtain information in the thermal range of the electromagnetic spectrum, are a suitable source of information in preparing thermal maps and estimating the radiation energy of the earth's surface. In this study, the productions related to the heat and land surface covers of the MODIS sensor of the Terra satellite have been used to investigate the spatio-temporal trend of heat islands and the relationship of these covers with the changes of heat islands.

1-2- Problem formulation and necessity of research

In the 20th century, urbanization happened at a high speed on a global scale. According to United Nations estimates, almost half of the world's people live in cities. In Western societies, this figure reaches more than 75% (UN, 1999).

According to the results of the general population and housing census of 2015, about 30% of Iran's 70 million population live in 13 cities with more than 500,000 people. These thirteen cities are: Tehran, Mashhad, Isfahan, Tabriz, Karaj, Shiraz, Ahvaz, Qom, Kermanshah, Urmia, Zahedan, Rasht and Kerman. Among these cities, the share of six cities with more than one million people is 22%, and the share of the city of Tehran with 7,800,000 people is 11% alone. (Iranian Statistics Center).

While the cities are developing, changes are made in the face of the earth. Buildings, streets and other infrastructure replace soil and vegetation. Surfaces that were usually permeable and moist before become impermeable and dry. The input energy absorbed by the sun may increase with changes in natural levels (Yamaguchi, 2004). This leads to a change in the energy balance of urban areas, which causes an increase in temperature (both on the surface and air temperature) in urban areas and finally the formation of thermal islands. Heat islands make summer weather conditions more difficult and the use of air conditioners more. Ozone conditions are affected by the emission, mixing and scattering of chemical reflections in the atmosphere, and urban heat islands lead to its intensification. In addition, with the increase in temperature, the hydrocarbon production of plants increases, which is one of the reasons for the increase in air pollution (Sailor, 2007). In addition to these obvious results of heat islands, this phenomenon has an effect on the local climate, such as changing the local wind pattern, the growth of clouds and fog, the number of lightning and the amount of precipitation. Recent studies in the past forty years have been able to quantitatively determine the role of the main phenomena affecting the formation and continuation of urban heat islands. Traditionally, the main and common source of climate data, including air temperature, are meteorological stations. These stations only provide statistics for certain points. In some cases, the air temperature in a region or city is reported as a certain value, if this value is related to the location of a specific point of the city, and perhaps according to the ground cover and other conditions, the temperature is lower or higher in different parts of the same city. In order to solve this problem, various methods have been proposed to calculate and estimate meteorological data between stations. Among these methods, we can mention the use of the relationship between temperature and height and different interpolation methods such as the weighted average of the inverse distance and different forms of kriging (Wang et al. 2004). The method of relationship between temperature and height is suitable only for small mountainous areas and interpolation methods for areas with uniform conditions. Since land surface temperature is highly dependent on the type of land surface cover, different interpolation methods can have acceptable accuracy when using satellite data to consider land surface cover as well (Yang et al. 2004). In recent years, remote sensing technology has been widely used in the study and monitoring of urban heat islands in different continental and regional scales by providing images with different resolutions. Quantitative physical data produced by satellites make us understand more about urban and non-urban environments. Especially during the last two decades, the great need for earth surface temperature information for environmental studies and land resource management activities has turned the estimation of earth surface temperature by remote sensing technology into one of the interesting topics of scientific interest (Sobrino, 2004).

Using the science of remote sensing, important physical properties that are the parameters that determine the constituent materials and the composition and structure of the city cover can be extracted to check the energy budget of the city surface and observe the effect of urban heat islands. In addition, remote sensing thermal images, especially high-resolution images, have the ability to generate simultaneous thermal data for the entire city and in a wide area coverage (Nichol, 1998).