بررسی تأثیر پوشش گیاهی بر تغییرات دمای سطحی زمین شهرستان اصفهان با استفاده از داده های سنجش از دور (مقاله علمی وزارت علوم)
درجه علمی: نشریه علمی (وزارت علوم)
آرشیو
چکیده
دمای سطح زمین یا دمای رویه زمین در سطح شهرها و مناطق شهری نسبت به محیط اطراف به طور چشمگیری بیشتر است که به عنوان جزیه گرمایی شناخته می شود. این پدیده اگر از حد مشخصی بیشتر شود باعث ایجاد مشکلاتی برای ساکنان شهر می شود. در پژوهش حاضر اثر وجود پوشش گیاهی بر روی میزان جزیره حرارتیِ شهری شهرستان اصفهان بررسی شد. بدین منظور، روند تغییرات دمایی سطح زمین منطقه مطالعه شده و ارتباط آن با پوشش سطحی با استفاده از محصولات دمای سطح زمین (LST) سنجیده مودیس، مکان هایی با جزیره حرارتی بررسی شد. همچنین، برای تهیه نقشه تراکم پوشش گیاهی در بازه زمانی 2020- 2001 میلادی از شاخص تفاضل پوشش گیاهی نرمال (NDVI) داده های ماهوره لندست استفاد شد. بررسی تغییرات زمانی سالانه دمای رویه شهرستان اصفهان نشان می دهد که دما در طی این دوره افزایشی است؛ به طوری که سال 2011 با میانگین دمای سالانه21/37 درجه سلسیوس به عنوان گرم ترین و سال 2012 با میانگین دمای سالانه 7/33 درجه سلسیوس به عنوان سردترین سال در دوره زمانی مطالعه شده است. نتایج مربوط به بررسی پوشش گیاهی نیز نشان داد که اراضی بایر بیشترین دما و اراضی با پوشش گیاهی، کمترین دما را دارند. جزایر حرارتی نشان داد که مناطق با کاربری صنعتی و مکان هایی با تراکم بالای جمعیت (پرترافیک)، هوایی آلوده و بافتی فشرده و فرسوده دارند. توسعه کاربری شهری در طول دوره مطالعه، بسیار محسوس بوده است که به همین نسبت نیز کاهش پوشش گیاهی را به همراه دارد و نشان دهنده افزایش دمای شهری است.The Effect of Vegetation Covers on Surface Temperature Changing of Isfahan City (2001-2020)
The surface of the earth or the top of the earth at the level of cities and urban areas becomes significantly higher than the surrounding environment, which is known as the thermal component. If this phenomenon is higher than a certain limit, it will cause problems for the city residents. But one of the most important factors that can play a very important role in controlling this phenomenon is the presence of vegetation, which is mainly a significant part of this coverage in urban areas. In this study, the effect of vegetation cover on the amount of urban heat island in Isfahan City was investigated. For this purpose, the surface temperature of the city and its relationship with the surface cover were investigated using the land surface temperature (LST) products of the MODIS sensor in places with heat islands by applying the Normalized Difference Vegetation Index (NDVI) of Landsat satellite data during the period of 2001-2020. Examining the annual changes in temperature in Isfahan shows that during this period, the temperature is generally increasing, so 2011 with an average annual temperature of 37.21 degrees Celsius is the hottest year and 2012 is the coldest year with an average annual temperature of 33.7 degrees Celsius. The most apparent thermal islands were observed in areas with industrial use, high-traffic places with severe air pollution and population density, and places with weak vegetation, areas with dense and worn-out textures.Keywords: LST, Landsat Satellite, Normalized Difference Vegetation Index (NDVI). IntroductionIn today's growing world, there is unprecedented urbanization and urban development, which have become factors affecting the air temperature around urban areas. This temperature causes the creation of a heat island in these areas compared to the surroundings, and as a result, it can play a fundamental role in air quality and consequently public health. In one study conducted by Taghizadeh and Mazidi (2019), the variability of heat island risk based on changes in land use and land cover was investigated in Isfahan. The results of this research showed that the expansion of the city cannot be the main cause of the increase in the surface temperature and the expansion of the heat island, but the change in the use of other lands has also been effective in increasing or decreasing the temperature. The purpose of the present study is to investigate the effects of vegetation in adjusting the surface temperature of the ground in Isfahan City. Depriving the cities of vegetation will cause the temperature to rise, especially in the summer season in big cities like Isfahan. Isfahan region is also facing the mentioned problems due to the large size of urban areas and rapid growth in recent decades. In this regard, Landsat and MOADIS satellite data are used. Materials and MethodsTo achieve the purpose of this study, satellite data were used. To investigate the effects of the independent variable (i.e. vegetation covers) at the city level, the MODIS sensor data of the Terra satellite were used in the period from 2001 to 2020. Landsat satellite data, which have a pixel size of 30 meters in the period from 2001 to 2020, were used to investigate the amount of vegetation (NDVI index) in the city of Isfahan. In order to collect the data, first, satellite images were received by referring to the United States Earth and Science website https://earthexplorer.usgs.gov. The NDVI index was used in the period from January 2001 to December 2020 to investigate the patterns of vegetation changes and fluctuations in time and place. For this purpose, raw images were obtained from the NASA website, which included 240 monthly time series images of vegetation covers. Research FindingsThe results of the analysis showed that the average annual temperature of the surface of the earth in this city is 35.6 degrees Celsius. According to the annual surface temperature map for the city of Isfahan, the minimum temperatures are completely consistent with the peripheral heights of the city, which can be seen in the form of spots in the northern parts (northern elevations of the foothills) and southwest areas (southern elevations of Shahreza). These parts show a temperature between 19 and 25 degrees Celsius. The temperature of 25 to 30 degrees is scattered around the mentioned parts as well as around the city of Isfahan and the Gav Khouni swamp. The largest temperature zone in the annual map includes the temperature of 35 to 40 degrees, which covers most of the city. The maximum temperature that shows the hottest spots is located in the central part of the city. In order to investigate the effects of the presence of vegetation and the amount of vegetation density in reducing the surface temperature in the urban area of Isfahan, Landsat satellite data were used, and the NDVI vegetation index was applied to these data. Then, a map and the amount of vegetation density were obtained. Since the map of vegetation cover and surface temperature was prepared exactly on a specific and simultaneous date, it is easy to visually observe the moderating role of vegetation covers in different parts of Isfahan. With the investigations carried out, it was precisely determined that wherever there is vegetation in Isfahan, the minimum temperature corresponds exactly to these parts. In parts of the city that are devoid of vegetation, which mainly corresponds to urban constructions or barren lands, a significant increase in the temperature of the surface of the earth can be seen. Therefore, the moderating effect of vegetation on the temperature of the city and the simultaneous reduction of the heat island in the studied area cannot be ignored. The major part of the concentration and density of vegetation in this city exactly corresponds to the passage of Zayandeh Rood. Discussion of Results and ConclusionThe development of urbanization causes the reduction of barren lands with high temperatures and the formation of a layer of relatively lower temperatures than barren lands in residential areas. Vegetation has a reducing effect on urban built surfaces such as busy streets and changes in land use such as agricultural land to residential use. Being adjacent to barren lands in the city has intensifying effects on high temperatures and hot spots. In fact, the results of this study show that, according to the investigations carried out on the Landsat satellite data in Isfahan, there is a strong correlation between the presence of vegetation and the decrease in the temperature of the city. In this regard, in the parts of the city where the density of vegetation increases, the surface temperature is greatly reduced, and the moderating role of vegetation can be seen well, but the temperature increases completely as you move away from the vegetation. Persian
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