Geographic Data
Foroogh Mohammadi Ravari; Ahmad Mazidi; Zahra Behzadi shahrbabak
Abstract
Extended Abstract
Introduction
Replacing natural vegetation cover with impermeable urban surfaces) stone, cement, metal, etc.) has resulted in increased land surface temperature which is considered to be the most important problem of urban areas. Distinct temperature difference between the city and ...
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Extended Abstract
Introduction
Replacing natural vegetation cover with impermeable urban surfaces) stone, cement, metal, etc.) has resulted in increased land surface temperature which is considered to be the most important problem of urban areas. Distinct temperature difference between the city and the surrounding areas is called heat island (Melkpour et al., 2018). Increased land surface temperature and resulting heat islands in urban areas built without proper preplanning (Khakpour et al., 2016) especially in developing countries such as Iran experiencing a rapid growth rate have resulted in widespread environmental problems. Heat islands mainly occur due to the presence of man-made surfaces which prevent the reflection of sunlight and result in temperature increase. In general, urban heat islands result in increased air and land surface temperature and thermal inversion (Gartland, 2012).
Methodology
The present study applies a statistical-analytical research method based upon statistical data received from meteorological stations and extracted from satellite images. Climatic data recorded from 1976 to 2020 in Yazd Meteorological Station were retrieved from the General Meteorological Department of Yazd Province and used to measure temperature changes. Urban climate studies mainly take advantage of long-term patterns and thus, the present study has applied the common Man-Kendall method to measure the trend of temperature changes in warm season (July, August, and September). Also, satellite images collected by Landsat 4-8 in a 33-year period, including four statistical periods with a time interval of 11 years (the average recorded in July, August and September of 1987, 1998, 2009 and 2020), have been used to extract heat islands of Yazd city in warm seasons. These images collected under clear weather conditions were retrieved from the United States Geological Survey website (http://glovis.usgs.gov/) in the WGS-1984 UTM image system. NDVI index was used to investigate the vegetation cover. Main land uses discussed in the present study included barren lands, urban areas, vegetation cover and roads. Sample land uses were collected from Google Earth and visually interpreted in ArcMap. Maximum likelihood algorithm was used for the classification process. Finally, Land Surface Temperature was extracted from satellite images and compared with air temperature trend using the Mann-Kendall test.
Results & Discussion
Results indicate that due to thicker vegetation cover in summer, there has been a negative relationship between the vegetation cover and land surface temperature. In other words, land surface temperature has increased with decreased vegetation cover and vice versa. Types of land use identified in satellite images collected from Yazd city have showed that the city has experienced a widespread physical expansion during the 33-year statistical period regardless of the season under investigation and thus, built-up urban land use class has expanded significantly. As a result, vegetation cover has experienced a negative trend and decreased. Land surface temperature extracted from thermal images of Yazd city has proved parts of northwest and south of the city to be the core of its heat islands. This is due to the presence of barren lands, lack of evapotranspiration mechanisms, high heat absorption capacity and low conduction capacity. Man-Kendall test has found a significant increasing trend for temperature especially in recent years in which the temperature has increased about 2.3 °C. This is most possibly due to the increasing trend of urban population in recent decades, followed by increased residential structures and resulting heat island phenomenon.
Conclusion
In general, classification of urban land use types in Yazd has shown a significant physical expansion of the city during the statistical period. This physical development has occurred in all directions; beginning from the central and northeast-southeast parts, and moving towards northwest-southwest parts. Maximum NDVI was observed in a strip along the central part of Yazd in which vegetation cover is thicker. Green spaces are also observed in some areas of the city. Color spectrum of the LST map has shown relative changes of the ambient temperature in various parts of the city. High and very high temperature (between 41.5 and 50 °C) show the location of the heat islands on LST maps. Also, areas with a deep red color and a temperature above 50 °C have formed hot clusters formed or strengthened between 2009 and 2020 in the west and southwest parts of the city. Satellite images and related graphs have showed that in 2020, Yazd have witnessed a sharp increase in temperature and a heat island. Temperature data of Yazd Meteorological Station and Man-Kendall test have shown a significant increasing trend (about 2.3°C), especially in recent years. These are related to the urban population growth in recent decades, followed by increased urban structures (residential-commercial) and heat island phenomenon.
Saeed Maleki; Ali Shojaeean; Ghasem Farahmand
Abstract
Extended Abstract
Introduction
Urban heating is one of the most well-known forms of local manipulation of the climate by mankind, so that changes in the use of land cover in urban areas can lead to an increase in urban temperatures relative to the air temperature in rural areas. This phenomenon has ...
Read More
Extended Abstract
Introduction
Urban heating is one of the most well-known forms of local manipulation of the climate by mankind, so that changes in the use of land cover in urban areas can lead to an increase in urban temperatures relative to the air temperature in rural areas. This phenomenon has been quantified in the form of the Urban Heat Islands (UHI) and has been studied and recorded for over 150 years in various cities of the world. The effect of the Urban Heat Island refers to an increase in the temperature of each man-made area, with respect to the surrounding surfaces. This phenomenon in urban areas refers to an increase in the temperature of cities with respect to the rural and suburban areas. On the other hand, the heat island directly affects the health of urban wildlife. Each year, in the United States, about 1,000 animals die due to the temperature rise, and more than that are destroyed because of the urban air harmful compounds. These changes in the pattern of winds have very important and dangerous consequences, such as the transmission of air pollution and dispersed toxic particles from cities to the suburbs, to disruption the people’s comfort within the city, which is why the heat islands are now considered as the causes of worrying about people’s health. Moreover, the heat islands change the wind patterns in the cities and surrounding areas. The suburban breeze is a dominant phenomenon in cities that are located on a flat land. The presence of heat islands, in addition to temperature changes, causes changes in land processes such as early flourishing of urban plants and longer growing season.
Materials and Methods
The present research has been an applied research in terms of targeting and a field-analytical one in terms of data collection. In order to reach the final goal of the research, the meteorological statistics of the synoptic meteorological station of Urmia city was studied first. Then, the study of different regions of the city was done in terms of temperature given the 9 stations set up inside the city and the suburbs. The data of 9 stations set up in the city was adjusted by installing a dry temperature sensor at an altitude of 180 cm, in cooperation with the municipality of Urmia, at a minimum and maximum daily rate of two hours (7:30 am and 5:30 pm) in hourly, daily and monthly forms. It should be noted that, the desired statistical period is from April 21, 2015 to July 22, 2015, and the readout pattern is on a daily basis, and its output is in the form of 1st to 4th of each month (days 7, 15, 22 and 29 of each month).
Result and conclusion
The rapid growth of urbanization and the increase in the population of Urmia city has caused significant changes in the physical and natural conditions of the city. This increase and expansion of the urbanization trend has affected some of the meteorological quantities in a way that, the performed studies indicate that the minimum temperature of Urmia city during the twenty year period is increasing in all months of the year compared with the neighboring stations. Nevertheless, specifying the limits of the Urmia heat island requires more precise studies. The study of the isothermal map of the average maximum temperature in the months of May, June and July, 2015 indicates that the Velayat-e-Faqih square station with a temperature of 29.41 degrees Celsius accounts for the highest temperature compared with eight other stations and in fact, has formed the center of the heat island. At the same time, the station for the license plate exchange center in the city of Urmia with a maximum temperature of 22.27 Celsius, is the coolest station compared to other stations, indicating a heat difference of 6.64 Celsius in the city. According to the above map, the intensity of the heat island decreases by distancing from center of the city. But the most important result that can be obtained from the above maps is the extension of maximum temperature curve toward parts of the East and South-east. The reasons for the high average temperature at the station of the municipality town and the station of Golman Khane can be summarized as follows:
The existence of 90% of industrial uses, workshops and factories at the edge of these stations
Wind flow
Given that wind is the most effective barrier against the formation of heat islands, the combination of the wind field with the pattern of heat island’s spatial variations shows significant results, which is a sign of the great impact of wind on the quality of formation of the heat island. The wind contributes to the extension of the heat island’s curve through the transfer of suspended particles and gases existing in the urban atmosphere.
