چکیده:
در اکوسیستمهای شهری، بررسی الگوی ناهمگنی محیط حرارتی و عوامل مؤثر بر آن در ارزیابی اکولوژیک و آسایش حرارتی محیط شهری ضروری است. از این رو هدف پژوهش حاضر بررسی ناهمگنی مکانی جزایر حرارتی و برودتی منطقۀ شهری با تأکید بر نقش پوشش اراضی در ایجاد آن و همچنین ارزیابی اکولوژیک محیط حرارتی است. از آنجا که اثرات جزایر حرارتی در فصل گرم سال اهمیت بیشتری دارد، این مطالعه در تیرماه سال 1399 با استفاده از تصاویر ماهواره لندستـ8 در منطقۀ شهر کرج انجام شد. در این پژوهش، نقشۀ دمای سطح زمین با استفاده از الگوریتم تکپنجره و نقشۀ پوشش اراضی با روش حداکثر شباهت استخراج شد. سپس برای تعیین نقش پوشش اراضی در ایجاد جزایر حرارتی و برودتی، شاخص سهم برای سه طبقۀ عمدۀ پوشش اراضی محاسبه گردید. در ادامه، از نمایۀ واریانس زمینۀ حرارتی شهر (UTFVI) بهمنظور ارزیابی اولیۀ اکولوژیکی استفاده شد. نتایج محاسبۀ شاخص سهم نشان داد اراضی بایر و رهاشده بیشترین نقش (53/1) را در تشکیل جزیرۀ حرارتی داشت، درحالی که کمترین سهم بهترتیب مربوط به اراضی انسانساخت (2/0) و طبقۀ باغات، فضای سبز و کشاورزی (76/0) بود. همچنین یافتهها نشان داد نقاط داغ حرارتی در شهرکهای صنعتی حاشیهای و اراضی بایر (حوالی فرودگاه پیام) در جنوب منطقۀ مورد مطالعه واقع شده است. نتایج نمایۀ واریانس زمینۀ حرارتی شهر نشان داد مناطق داخل شهر (بهویژه بافت قدیمی و متراکم) از لحاظ اکولوژیکی و آسایش حرارتی، وضعیت بهتری از مناطق تازهتوسعهیافتۀ حواشی شهر دارند. بهطور کلی از نتایج این پژوهش میتوان در فرایند برنامهریزی شهری، بهمنظور بهبود وضعیت اکولوژیک شهر از دیدگاه حرارتی، استفاده کرد.
Temperature is one of the critical environmental parameters which is spatially heterogeneous, affecting biological, physical, and social interactions within an urban ecosystem. Therefore, the main purpose of this article is to investigate the contribution of various land covers in forming urban heat islands (UHIs) and urban cool islands (UCIs) and determining the pattern of UHI-UCI in an arid and semi-arid urbanization region of Karaj, Iran in July 2020. To achieve the goal, initially, the land surface temperature (LST) was retrieved using mono-window algorithm; maximum likelihood method was applied to generate the land cover/land use (LULC) map using Landsat 8 OLI -TIRS data. Then, the contribution index (CI) of each LULC in creating UHI and UCI was calculated. The thermal environment of the city was evaluated using Urban Thermal Field Variance Index (UTFVI). The results showed that built-up surface (0.2) and green space (0.76) contributed the most in creating UCI, while the barren cover played a major role (1.53) in creating UHI. In addition, the urban hot spots were seen in the industrial zone and bare land (adjacent to the Payam airport) in the southwest of the region. The UTFVI analysis showed that the central areas of the city (old and dense residential areas) were ecologically better as compared to the urban periphery. Therefore, it is necessary to implement mitigation strategies in the marginal areas of the study area. In general, the results of this research can be helpful in urban planning to moderate urban temperature in ecologically stressed zones. Extended Abstract 1-Introduction Temperature is one of the critical environmental parameters affecting biological-physical-social interactions of the urban ecosystem. In urban areas, the temperature is spatially heterogeneous due to extreme variation of land cover. One of the most well-known temperature-related phenomena in cities is the formation of urban heat islands (UHI), which endangers thermal comfort and ecological status. Moreover, determining hotspots with the aim of reducing the temperature is one of the important measures to maintain the temperature balance of the city. Current knowledge of the urban thermal environment is principally based on land surface temperature (LST) maps retrieved from satellite thermal sensors. Therefore, the main purpose of this paper included; 1) extraction of land surface temperature (LST) using mono-window (MW) algorithm from Landsat 8 satellite image; 2) determination of urban heat island and urban cool island (UHI and UCI) and thermal hotspots based on LST; 3) investigation of the relationship between land cover/ land use (LU/LC) with UHI and UCI by calculating contribution index, and 4) ecological assessment of the thermal environment using Urban Thermal Field Variance Index (UTFVI). 2-Materials and Methods Urban region of Karaj includes a group city, a climatically arid and semi-arid region, which was taken as the study area in current research. Since the effects of the thermal environment are more important in the hot season, this study was conducted in July 2020. The land cover/ land use map was generated using the maximum likelihood method in five classes of built-up, agriculture, orchards and green space, rangeland, bare land, and forest. The LST was retrieved using a mono-window algorithm to identify UHI-UCI. In addition to the identification of UHI and UCI, thermal hot spots were also determined across the city. Then, the contribution index was calculated in order to quantify the role of the three major land cover classes of built-up, vegetation, and bare land in forming UHI-UCI. After all, we used the Urban Thermal Field Variance Index to evaluate the ecological circumstance of the environment. Based on the thermal threshold of the UTFVI in terms of ecology and thermal comfort, the area was divided into three classes called good, normal, and poor. 3- Results and Discussion The overall accuracy and kappa coefficient of the land cover map were 87% and 83%, respectively. The accuracy of the LST map was evaluated using the data of two meteorological stations, indicating MAE and RMSE of 0.4 and 0.44, respectively. The results of this research showed that built-up cover (0.2) and agriculture and green space (0.76) contributed the most to creating UCI. However, the barren cover and abandoned farmlands played a major role (1.53) in creating UHIs due to the lack of shading effects of the building and evapotranspiration compared to built-up area and vegetation cover. Surprisingly, UCIs were formed in the densely built-up area and green spaces. The Urban Thermal Field Variance Index analysis showed that the inner and central areas of the city (old and dense part) were better in terms of ecological circumstances and thermal comfort than the newly-developed areas on the outskirt of the city. In addition, hot spots were seen in the industrial zone and bare land (adjacent to the Payam Airport) in the southwest of the region. In other words, the pattern of LST in the study region, which has an arid and semi-arid climate, is different from cities located in humid climate with abundant vegetation cover such as European and tropical cities. 4- Conclusion In general, it can be concluded that the mono-window algorithm is an appropriate method to retrieve LST in urban areas. In the study area, which is climatically located in an arid and semi-arid zone, dense man-made areas were cooler than marginal and low-density man-made cover during the day in the warm season. The initial ecological assessment was performed using Urban Thermal Field Variance Index. In order to improve the ecological situation in poor areas, temperature mitigation measures such as developing green space can be used according to cost analysis and expert opinions. As a recommendation, establishing complementary research focusing on the arrangement and configuration of the different landscape elements can lead to providing a more accurate analysis of the thermal environment pattern.
خلاصه ماشینی:
از اين رو هدف پژوهش حاضر بررسي ناهمگني مکاني جزاير حرارتي و برودتي منطقۀ شهري با تأکيد بر نقش پوشش اراضي در ايجاد آن و همچنين ارزيابي اکولوژيک محيط حرارتي است .
از بين اين شاخص ها، نمايۀ واريانس زمينۀ حرارتي شهري (UTFVI) که براي ارزيابي اکولوژيک محيط حرارتي استفاده ميشود، به علت ارتباط مستقيم با دماي سطح زمين ، کاربرد بيشتري دارد (آلفرايهت و همکاران ، ٢٠١٦؛ لي و همکاران ، ٢٠١٣؛ ليو و ژانگ ٧، ٢٠١١؛ مک اي ٨ و همکاران ٢٠١٢).
با اينکه مطالعات زيادي دربارٔە تشکيل جزاير حرارتي صورت گرفته ، الگوي تشکيل اين پديده در اقليم خشک و نيمه خشک در مطالعات اندکي بررسي شده است ؛ به طوري که در پژوهش هاي پيشين ، پيشنهاد شده است دماي سطح در مناطق جغرافيايي مختلف بررسي شود تا بتوان به تعميم مناسب تري درمورد ارتباط دماي سطح زمين و پوشش اراضي در منطقۀ خشک و نيمه خشک دست يافت (رسول و همکاران ، ٢٠١٥).
Urban morphology and landscape structure effect on land surface temperature: Evidence from Shiraz, a semi-arid city.
Remote sensing image-based analysis of the relationship between urban heat island and land use/cover changes.
Effects of landscape composition and pattern on land surface temperature: An urban heat island study in the megacities of Southeast Asia.
Remote sensing of the urban heat island effect across biomes in the continental USA.
Temperature-land cover interactions: The inversion of urban heat island phenomenon in desert city areas.
Remotely sensing the cooling effects of city scale efforts to reduce urban heat island.
Land surface temperature retrieval from CBERS-02 IRMSS thermal infrared data and its applications in quantitative analysis of urban heat island effect.