فضاهای شهری به واسطه درهم آمیختگی عناصر انسانساخت و عوارض طبیعی، شرایط محیطی متفاوت و پیچیدهتری از محیطهای طبیعی دارند. امروزه در منطقهبندی اقلیمی فضاهای شهری، رویکرد متخصصان اقلیم شهری بر توجه و استفاده ترکیبی از عوامل شهری و طبیعی است. زونهای محلی اقلیم به طبقهبندی آبوهوایی فضاهای شهری با توجه و تمرکز بر ساختار فیزیکی و پوشش سطحی شهر میپردازد. این روش طبقهبندی دارای 17کلاس با ویژگیهای پوششی و فیزیکی متفاوت است. برای انجام پژوهش از سه نوع دادههای هواشناسی، تصاویر ماهوارهای و لایههای اطلاعات مکانی استفاده شد. تصاویر برای دو دوره زمانی تابستان و زمستان، لایههای اطلاعات مکانی شهر تهران و حومه آن شامل دادههای کاربری/پوشش اراضی و طبقات ساختمانی شهر و دادههای جوی دما، بارش، سرعت و جهت باد در دوره زمانی 20 ساله از ایستگاههای هواشناسی داخل شهر تهیه شدند. فرایند پردازش دادهها در نرمافزار ساگا-جیآیاسS، نمونهبرداری در گوگل ارتس و طبقهبندی و خروجی اطلاعات در آرک/جیآیاس انجام شد. نتایج طبقهبندی اقلیم محلی تهران نشان داد، اقلیمهای محلی با بافت متراکم و ارتفاع متوسط(کلاس 2) و متراکم و کوتاه (کلاس 3) غالب هستند. این دو کلاس اقلیم محلی که با بار گرمای محیطی بالا و ظرفیت تهویه ضعیف شناخته میشوند، عموماً در مرکز و مناطقی از شمالشرق تهران متمرکزند. همچنین حومه شمال و شمالشرق با پهنههای پوشش درختی و طبیعی (یعنی طبقات اقلیمی درختان متراکم تا بوتهزار) و حومه جنوبی شهر با اراضی کشاورزی و علفزار مشخص شدند؛ این طبقات اقلیمی قابلیت تأمین هوای خنک و مطلوب برای داخل شهر را دارند. در نتیجه تقویت کریدورهای سبز و گذر هوای شمالی ـ جنوبی برای کاهش بار گرمای مرکز شهر و افزایش ظرفیت پویایی آن پیشنهاد میشود.
عنوان مقاله [English]
Local Climate Zoning of Tehran metropolitan base on physical structure
- Climatic zoning of Tehran was conducted using the latest and most accurate method available.
- This climatic zoning used the processing of Landsat 8 satellite images and sampling in Google Earth.
- 17 climatic zones were obtained according to physical characteristics and land surface cover.
- The LCZ model focuses on the thermal loads of the city, which are affected by building density and land cover/use changes.
- The central and eastern areas of Tehran, due to the high density of buildings, and the southwestern areas of the city, due to industrial and warehouse land use, have high thermal loads.
Urban spaces have different and more complex environmental conditions than natural environments because they combine human-made elements and natural features. Today, urban climate specialists focus on a combination of urban and natural factors when zoning urban spaces.
The Local Climate Classification (LCZs) is a new and systematic classification system for urban spaces proposed by Stuart and Oke (2012). LCZs classify climates according to the physical structure of the city. Each LCZ is characterized by one or more distinctive features, such as land cover, height, and the distance between trees and buildings.
Local Climate Zoning classifies the climate of urban spaces by focusing on the city's physical structure and surface coverage. The LCZ classification has 17 different classes, each of which represents a unique set of characteristics. LCZ classes are individually identified by one or more distinctive characteristics, such as land cover or height, the distance between trees and buildings. Classes 1 to 10 focus more on the physical structure created by humans, while classes A to G focus more on the natural aspect of the city.
The Local Climate Zoning (LCZ) method was extracted and presented by Stewart and Oke (2012) from the Urban Climate Zones (UCZ) method. This method is presented with an emphasis on land cover characteristics and building density for large cities.
In this method, 10 climate zones are specified for urban built spaces and 7 climate zones for natural spaces. The most important data required in this method are Landsat satellite images, which are prepared in both winter and summer seasons to accurately identify the land surface cover. Additionally, for each of the 17 climate classes, it is necessary to take samples in Google Earth to use those samples in the image processing process. Therefore, the accuracy and quality of the map of local climate zones depends on the accuracy of sampling.
Three types of data were used in this study: meteorological data, satellite images, and spatial information layers.
- Meteorological data included temperature, precipitation, wind speed, and wind direction data from the Doshan Tappeh, Geophysical, and Mehrabad meteorological stations in Tehran for the past 20 years.
- Satellite images of the city of Tehran were used for two periods: summer and winter.
- Spatial information layers included land use data, land cover, and building floors of Tehran.
To create a map of the local climate classes in Tehran, the satellite images were converted to a spatial resolution of 100 meters in the SAGA-GIS environment. The measured area was then cut and saved in kml format and added to the Google Earth program. In Google Earth, samples of each climatic class were collected. This stage was the most important and decisive stage of the research, and it was conducted with great accuracy and patience using many samples.
Results and Discussion
The city of Tehran has a diverse range of local climate classes (LCZs) due to its diverse natural and human environments. Tehran is a heterogeneous metropolis in terms of its form and function, and this heterogeneity is reflected in the distribution of LCZs.
The results of this study showed that the most common LCZs in Tehran are:
- Dense texture and medium height (LCZ 2): These LCZs are characterized by high ambient heat load and poor ventilation capacity. They are generally concentrated in the central and northeastern parts of Tehran.
- Dense and short (LCZ 3): These LCZs are also characterized by high ambient heat load and poor ventilation capacity. They are found in other parts of the city, such as the southern and southwestern suburbs.
- Low-rise and mid-rise (LCZ 4 to LCZ 6): These LCZs are characterized by lower ambient heat load and better ventilation capacity. They are found in the outer parts of the city, such as the northwestern and southeastern suburbs.
- Barren land and agricultural land (LCZ 7 to LCZ 9): These LCZs have the lowest ambient heat load and best ventilation capacity. They are found outside the city limits.
The distribution of LCZs in Tehran is affected by a number of factors, including:
- The density of buildings
- The height of buildings
- The presence of vegetation
- The topography
- The proximity to water bodies
The high density of buildings in the central and northeastern parts of Tehran is the main reason for the predominance of LCZs 2 and 3 in these areas. The low density of buildings in the outer parts of the city is the main reason for the predominance of LCZs 4 to 6 in these areas. The presence of vegetation helps to reduce the ambient heat load and improve ventilation, while the proximity to water bodies also helps to cool the air.
The distribution of LCZs in Tehran has important implications for the city's climate and environment. The high ambient heat load and poor ventilation capacity of LCZs 2 and 3 can contribute to the formation of the urban heat island effect, while the lower ambient heat load and better ventilation capacity of LCZs 4 to 6 can help to mitigate this effect. The presence of vegetation can also help to improve air quality and reduce noise pollution.
Overall, the distribution of LCZs in Tehran is a complex issue that is affected by a number of factors. The understanding of this distribution is important for the development of strategies to mitigate the effects of climate change and improve the city's environment.
The findings of this study have important implications for the planning and management of Tehran. Identifying areas at risk of high urban heat load and flooding can help to prioritize interventions to reduce these risks. For example, the city could plant more trees and vegetation to cool the air and reduce the urban heat island effect. It could also improve the drainage system to reduce the risk of flooding.
Overall, this study provides a valuable contribution to the understanding of the urban climate of Tehran. The findings can be used to develop strategies to improve the livability of the city and reduce the risks of heat stress and flooding.