بررسی رابطۀ جزایر حرارتی با محدوده‌های فضای سبز و آشکارسازی تغییرات آن (مطالعۀ موردی: شهر کرمان)

هدف از این مطالعه، بررسی تاثیر پوشش گیاهی موجود در شهر، در قالب فضای سبز، بر دمای سطح زمین و همچنین شناسایی جزایر حرارتی شهر کرمان است. محاسبۀ دمای سطح زمین (lst) به ‌روش معکوس، تابع پلانک با استفاده از تصاویر ماهوارۀ لندست‌‌8 در محیط سامانۀ گوگل ارث انجین انجام گرفت. دمای سنجیده‌شده به‌صورت میانگین دو تصویر در ماه‌های میانی چهار فصل بهار، تابستان، پاییز و زمستان سال‌های 1392، 1395 و 1399 محاسبه شد و به منظور ارزیابی کاراییِ روش مورد استفاده در محاسبۀ دما از روش های دفتر علوم لندست و پنجره مجزا برای شماری از تصاویر استفاده گردید. ارتباط پوشش ‌گیاهی با دمای سطح زمین، محاسبه‌شده برای شهر کرمان، و اثر آن بر این دما به روش های هم‌بستگی و انتخاب بافری حلقه ای، در فواصل 50، 100، 150 و 200 متری بررسی شد. در نهایت تغییرات فصلی آن ها با استفاده از شاخص خودهم‌بستگی موران بررسی شد و تحلیل تغییرات موقعیت آن، هم به صورت روند تغییر فصل‌به‌فصل و هم به صورت روند کلی، انجام گرفت. نتایج این مطالعه نشان داد که روش معکوس تابع پلانک و روش دفتر علوم لندست نسبت به روش پنجره مجزا نتایج دقیق تری داشتند. بین مساحت پارک و مقدار دمای آن ارتباط وجود دارد و کمترین دماهای محاسبه‌شده به‌ازای فضاهای سبز مربوط به پارک های با بیشترین وسعت است. تحلیل آزمون هم‌بستگی نشان داد که در تمام فصول سال، دمای سطح زمین با شاخص تراکم پوشش گیاهی رابطۀ معکوس دارد؛ همچنین مقدار و شدت این هم‌بستگی منفی بسته به فصل متفاوت است. بیشترین مقدار هم‌بستگی منفی، 0.48 بود که در تابستان سال 1392 ثبت شد. کمّی سازی تاثیر پوشش گیاهی بر نوسان دمای محیط پیرامون نشان داد که با افزایش فاصله از هسته های شناسایی‌شده به عنوان پوشش گیاهی، دمای سطح زمین افزایش می‌یابد، به نحوی که به طور متوسط در فاصلۀ 200 متری از مناطق دارای پوشش گیاهی، دما 3 درجه افزایش داشته است که گواه آشکاری بر تاثیر پوشش گیاهی بر مقدار دمای اندازه گیری‌شده است. نتایج این مطالعه نشان داد که محاسبۀ دمای سطح زمین نتایجی قابل اتکا در زمینۀ مدیریت فضای شهری ارائه می کند که می تواند در راستای تصمیم گیری های آتی شهری مفید واقع شود.

Investigating the Relationship between Thermal Islands and Green Space Areas and Detecting its Changes (Case Study: Kerman City)

This study was conducted to investigate the effect of vegetation in the city in the form of green space on Land Surface Temperature (LST) and also to identify the thermal islands of the Kerman city. LST was calculated by inverse method Planck function using Landsat 8 in Google Earth engine. The calculated LST was calculated as the average of two images in the middle months of the four seasons of 2014, 2017 and 2020. Landsat Science Notebook and a split window were used In order to evaluate the efficiency of the method used in calculating the LST. The relationship and the effect of vegetation on the calculated LST for Kerman city have been done using correlation and selection of ring buffer at intervals of 50, 100, 150 and 200 meters. Finally, their seasonal changes were examined using Moran’s I autocorrelation index and its position changes were analyzed both as a seasontoseason trend and as a general trend. The results showed that the Planck function method and the Landsat Science Notebook method had more accurate results than the Split window method. There is a relationship between the area of the park and its temperature, and the lowest calculated temperatures for green spaces are related to the parks with the largest area. Correlation test analysis showed that in all seasons of the year, LST is inversely related to vegetation density index. Also, the amount and intensity of this negative correlation vary depending on different seasons. The highest negative correlation value of 0.48 was recorded for the summer in 2014. Quantifying the effect of green space on the ambient temperature fluctuation showed that, on average distance 200 meters from vegetated areas, the temperature has increased by 3 degrees resulting from increasing distance from the identified cores as green space; it is clear evidence indicating the effect of green space on the amount of measured temperature. The results of this study showed that the calculation of earth surface temperature provides reliable results in the management of urban space that can be useful in future urban decisions.Abstract Extended 1IntroductionUrbanization has many environmental consequences whose various forms have been manifested today. The difference between surface coverage in urban and nonurban areas creates fundamental changes in the nature of the builtup urban area. Urban heat island is an example of unintended climate change affected by the changes on the earth surface and the atmosphere as a result of the urbanization process. In most conducted studies on investigating surface temperature, plants have a very important role in temperature regulation and related environmental equations related. Therefore, monitoring and revealing the role of vegetation in regulating the earth surface temperature can help understand the correct temperature distribution on the earth surface, especially in urban environments and the city of Kerman is no exception. This study was conducted to investigate the effect of present vegetation in the city in the form of green space on earth surface temperature and also to identify the thermal islands of Kerman.2Materials and MethodsLand Surface Temperature (LST) was calculated by inverse method of Planck function using Landsat 8 satellite imagery (TIRS Sensor) in Google Earth engine system environment. The calculated LST was calculated as the average of two images in the middle months of the four seasons, spring, summer, autumn and winter of 2014, 2017 and 2020. In order to evaluate the efficiency of the method used in calculating the temperature, the methods of Landsat Science Notebook and a split window were used for a series of images. In addition to calculating the LST, Normalized Difference Vegetation Index (NDVI) was also used to monitor the spatial changes of green space in Kerman. Since it was important to study the trend of vegetation changes in the city of Kerman in the years under study, in order to study its fluctuation using the extended presence points (1) and absence (0) of green space True Skill Statistic (TSS) threshold method was used and plants were identified in the spring from 2014 to 2020. Direction of their changes was also calculated using Directional Distribution analysis in ArcGIS10.4.1. The relationship and effect of vegetation on the calculated LST for the city of Kerman was done using the methods of correlation and selection of ring buffer at intervals of 50, 100, 150 and 200 meters. The thermal island threshold was identified using a raster profile of a 25kilometer transect from southwest to northeast in QGIS 3.16. After calculating the LST of the earth and determining the range of the beginning of thermal islands, the trend of its changes during the period 2014 to 2020 and also their seasonal changes using Moran’s I autocorrelation index were investigated and analysis of changes in their position as a change of season, season and was also examined as a general trend.3 Results and DiscussionThe results of this study showed that the Planck function inverse method and the Landsat Science Notebook method had more accurate results than the Split window method. Accordingly, the results of the average indices of LST and vegetation showed that the calculated land earth surface temperature in the city center is higher than the outskirts of the city and the highest values of the calculated temperature are related to newly added sections to the outskirts of the city. Dense urban structures in the city center have lower temperatures than in the part of the city that has more rupture. On the other hand, there is a relationship between the area of the park and its temperature, and the lowest calculated temperatures for green spaces are related to the parks with the largest area.Correlation test analysis showed that in all seasons of the year, earth surface temperature is inversely related to vegetation density index. Also, the amount and intensity of this negative correlation varies depending on different seasons. The highest negative correlation value of 0.48 was recorded in the summer of 2013. The detected threshold in the ROC curve was identified as 0.1489 and the values of 96.6% and 94.5% were calculated as sensitivity and specificity for this value, respectively, which indicates the appropriate strength of the threshold in separating vegetation from other structures of the urban environment. Quantifying the effect of green space on the ambient temperature fluctuation showed that the temperature has increased by 3 degrees on average distance of 200 meters from vegetated areas as a result of increasing distance from the identified cores as green space which is clear evidence proving the effect of green space on the amount of temperature has been measured.The results of the analysis of space changes show that there is a growing trend in the area and number of green spaces in Kerman during the period of this study and the direction of changes in green space was to the west. Moran index analysis also showed that the thermal islands in the city of Kerman have change depending on the season under study and the most stable area has thermal islands in the common areas between zones 1 and 2 in the north of the city.4 ConclusionThis study highlights the role of vegetation in regulating earth surface temperature in Kerman. The results of this study showed that the calculation of earth surface temperature provides reliable results in the management of urban space which can be useful in future urban decisions.