نوع مقاله : مقاله پژوهشی

نویسندگان

• حسن سجادزاده ¹
• فاطمه قربانی ²

¹ استاد گروه شهرسازی، دانشکده هنر و معماری دانشگاه بوعلی سینا همدان

² کارشناسی ارشد، گروه شهرسازی، دانشکده هنر و معماری، دانشگاه بوعلی سینا، همدان، ایران

چکیده

با توجه به تغییرات اقلیمی و همچنین توسعه های شهری بدون توجه به کیفیت زیست محیطی، شکل‌گیری جزیره گرمای شهری به یکی از چالش‌های جدی عصر حاضر تبدیل شده است. هدف عمده این پژوهش، تحلیل وضعیت پوشش گیاهی و دمای سطح زمین جهت بررسی شکل گیری جزایر حرارتی شهری در شهر کرج است. به این منظور و در راستای آشکارسازی تاثیر فضاهای سبز در محیط‌های حرارتی شهر کرج، از داده‌های سنجش از دور سنجش از دور برای استخراج فضاهای سبز، دمای سطح زمین و پوشش زمین استفاده شده است. دمای سطح زمین با استفاده از تصاویر MODIS1 محاسبه شد. تغییرات پوشش گیاهی با استفاده از اطلاعات برداشت شده توسط سنجنده‌های مربوطه ماهواره لندست2 7 و 8 مربوط به سال های 2001 و 2021 استخراج شد، و بعد از اعمال تصحیحات لازم و بررسی تصاویر، اقدام به شناسایی تغییرات کاربری اراضی و نوع تغییرات آن گردید. نتایج بررسی‌ها نشان داد که اراضی بایر پیرامون شهر به صورت پیوسته دارای بالاترین دما و لکه های گرم هستند و محدوده‌های دمایی بسیار گرم را تشکیل می‌دهند. در محدوده‌ی مسکونی شهر نیز، جزایر حرارتی بر بافت فرسوده و محدوده های متراکم منطبق است. هم‌چنین تحلیل و بررسی نقشه‌های دمای سطح زمین نشان‌دهنده‌ی افزایش دمای سطح در شهر کرج است. درعین حال، واکاوی نقشه‌ها حکایت از رابطه‌ی قوی بین پوشش گیاهی و دمای سطح زمین در کلان شهر کرج دارد. نقشه‌های کاربری اراضی نیز نشان از کاهش مساحت پوشش‌گیاهی و افزایش کاربری انسان ساخت دارد. این موضوع به طور واضح نشان-دهنده‌ی این است که مهم ترین عامل در گسترش جزایر گرمایی و افزایش دما در بازه‌ی زمانی مورد بررسی، کمبود پوشش‌گیاهی بوده است. در نتیجه فضاهای سبز و پوشش گیاهی در شهرها به طور چشم گیری سبب تعدیل جزایر حرارتی شهری هستند. به این صورت که نواحی همچون: اراضی بایر و نواحی دارای پوشش گیاهی کمتر، دارای دمای بیشتری نیز می‌باشند. بنابراین، گسترش بام سبز و استفاده از پوشش گیاهی سازگار با اقلیم هر منطقه به عنوان راه حلی برای کاهش جزیرة گرمایی پیشنهاد می‌شود

کلیدواژه‌ها

• جزایر حرارتی شهری
• پوشش گیاهی
• تصاویر ماهواره ای
• کرج

موضوعات

• محیط زیست شهری

عنوان مقاله [English]

The Effect of Vegetation on Reducing the Urban Heat Island (Case Study: Karaj City)

نویسندگان [English]

• Hassan sajadzadeh ¹
• fatemeh ghorbanileylestani, ²

¹ Professor Of Urbanism in University of Hamadan Bu-Ali Sina University, Faculty of Art and Architecture, Hamadan, Iran

² M s Department of Urban Sciences, Faculty of Architecture, Bu-Ali Sina University, Hamedan, Iran.

چکیده [English]

The Effect of Vegetation on Reducing the Urban Heat Island

Case Study: Karaj City



Introduction

With the rapid growth of population, urbanization is gaining momentum where urban areas are developed with greater proportion resulting into changes in existing landscape, buildings, roads, and other supporting infrastructure. Such a change replaces open land and vegetation in the form of permeable surfaces with concrete surfaces which are impermeable and dry in nature.

The consequences of population growth and urbanization on the urban environment, climate, and water supply have caused a wide range of issues. One of the key impacts of rapid urbanization on the environment is the effect of urban heat island (UHI). Such a development leads to the formation of urban heat islands whereby urban regions experience warmer temperatures than their adjacent rural surroundings.

Urban Heat Island (UHI) is a growing problem worldwide and increase in the land surface temperature and the formation of heat islands in the metropolis ar n recent years, various studies continuously manifest that the increased ambient air temperature in cities caused by UHI phenomenon embraces enormous negative influences on social, environmental and economic dimensions of cities eas has become one of the environmental problems. The heat island affects the quality of urban life, including energy consumption, air quality, as well as human health.

Strategies to mitigate the Urban Heat Island represent an important objective in design and urban planning, especially in cities in hot climates. Mitigation of UHI is necessary for cities to adapt to climate change and enhance sustainable development at a city scale. Cooling cities with urban vegetation management is a sustainable solution for urban heat mitigation and to increase thermal comforts of urban residents.

Materials and Methods

Remote sensing is a powerful tool for environmental monitoring that can be used to help understand LULC and rapid urbanization and to estimate UHI and ndvi properties at the Earth’s surface.

The present paper, Land cover maps within the administrative boundary of karaj city were derived from the cloud-free Landsat (downloaded free from http://www.usgs.gov/) with a resolution of 30 m for the years 2001-2021. at first 2 images of the warm seasons of the year from 2001-2021 were extracted from Landsat satellite including Landsat 7 (ETM+), Landsat 8 (OLI/TIRS) sensors. After the necessary pre-processing, land surface temperature (LST), and normalized difference vegetation index(NDVI) land use patterns were calculated for monitoring the land use changes in karaj. The land covers were classified into three types (built-up land, vegetation, and barren land) using the maximum likelihood classification approach.

Therefore, the present study explored the relationship between LST and NDVI Karaj region of alborz. The relationship of LST with NDVI was examined using correlation analysis. We used a regression tree model to examine the nonlinear relationships between LST and normalized differential vegetation index (NDVI).

This study focused on tow objectives. Firstly, analyzing land surface temperature (LST), normalized difference vegetation (NDVI) indices. Secondly, investigating interrelationships among LST, NDVI. Finally, the environmental criticality index (ECI) was used to identify and analysis of the sensitive regions.

Discussion of Results

In this paper, the negative impact of Urbanization over a time and its effect on increasing trend of temperature and degradation of urban ecology was assessed using the Landsat thermal data and field survey of karaj city, alborz.

In karaj City, LST showed an increased trend from 2001 to 2021 years, as increase the maximum temperature in the period from 2001 to 2021 was 4 °C, while increase the minimum temperature of 19°C was observed from 2001 to 2021.

The result showed that the type of land use had an effect on LST. The results showed that the arid lands around the city have the highest temperature and form very hot temperature areas. The observed results showed that the central portion of the city exhibited the highest surface temperature compared to the surrounding open area, the areas having dense built-up displayed higher temperatures and the areas covered by vegetation exhibited lower temperatures.

The highest temprature of studied region is observed around the city due to existence of barren lands and in to the city around the industrial centers, around the airport, passenger terminal, around the metro stations, the highways and streets of heavily congested areas and urban decay context areas. At the same time, analyzing the land surface temperature maps in karaj indicate the areas without vegetation have a maximum LST and areas with high density vegetation have minimum LST.

The landuse maps also show the reduction of barren lands, vegetation and increasing the urban landuse. This indicates that the decrease in vegetation cover and increase in urban landuse were the most important factors in development of the heat islands in karaj. Also Land use maps also show a decrease in the area of arid lands and vegetation and increase urban use.

The findings show normalized difference vegetation index is strongly correlated with the variations of land surface temperatures. The correlation coefficient between LST and NDVI was negative and inverse. The highest environmental sensitivity was in the East and Northeast parts of the city were identified.

Conclusions

This paper has demonstrated the relationship between urban heat islands and Normalized Difference Vegetation Index in karaj city. Results indicated that the spatial distribution of the land surface temperature was affected by the land use-land cover change and anthropogenic causes.

The results illustrated that barren lands surrounding the city in continuous and dense have the largest urban thermal islands and forming very hot temperature limits and in the study area, extreme high-temperature zones were observed, possibly due to dense concrete surfaces.

Hence, the development of green roof vegetation and tailored to the indigenous climate is proposed as solution to mitigate urban thermal island and dealing with environmental crisis.

Keywords: Urban heat islands, vegetation, satellite images, Karaj

کلیدواژه‌ها [English]

• Urban heat islands
• vegetation
• satellite images
• Karaj