Urban Ecology
Elham Ghasemi; Zahra Nazemi; Safoura Mokhtarzadeh; Mahdi Suleimany
Abstract
Highlights:
- Investigates the correlation between environmental factors and UHI intensity in the Isfahan metropolitan area over 10 years.
- Utilizes MODIS Aqua & Terra data alongside Landsat 8 imagery for comprehensive UHI analysis.
- Establishes a significant relationship between UHI ...
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Highlights:
- Investigates the correlation between environmental factors and UHI intensity in the Isfahan metropolitan area over 10 years.
- Utilizes MODIS Aqua & Terra data alongside Landsat 8 imagery for comprehensive UHI analysis.
- Establishes a significant relationship between UHI and urban built density, vegetation, and water features.
- Determines vegetation as the most influential factor in mitigating UHI compared to other elements.
- Highlights the vital role of natural infrastructure in urban planning for UHI mitigation.
Introduction:
The Urban Heat Island (UHI) effect, characterized by a temperature increase in urban areas compared to their rural counterparts, presents considerable environmental challenges, impacting public health, urban energy systems, and city sustainability. This phenomenon, fueled by rapid urbanization and industrialization, exacerbates heatwaves, posing risks to public health. Understanding the UHI effect is essential for developing responsive urban planning strategies both spatially and institutionally. This study, centered on Isfahan, Iran, explores the correlation between UHI intensity and environmental factors, encompassing both built and natural attributes across five scenarios, including four seasons and one analyzing the ambient effect of the ZayandehRud river.
Theoretical Framework:
The UHI phenomenon involves complex interactions among various urban and environmental factors. The density of the built environment contributes to UHI exacerbation through heat storage and anthropogenic heat discharge. Air pollution, especially with greenhouse effects, directly influences heat-trapping and UHI formation. Conversely, green infrastructure and water bodies offer UHI mitigation through cooling effects. This study integrates theoretical basics from urban planning, climatology, and sustainable development for an analysis of how both natural and built elements correlate with UHI intensity in the Isfahan metropolitan area.
Methodology:
A mixed-method approach is adopted to address the multifaceted nature of Urban Heat Island (UHI) and its potentially correlated environmental factors. Land Surface Temperature (LST) data, crucial for delineating UHI, were extracted from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensors onboard NASA's Aqua and Terra satellites, covering a decade from 2011 to 2021. This extended timeframe facilitates the exploration of UHI patterns across various seasons, examining specific impacts during both the flow and dry periods of the ZayandehRud river, as well as distinguishing LST differences between daytime and nighttime periods—unlike Landsat Satellite Images.
Additionally, Landsat 8 images are utilized to process the Normalized Difference Vegetation Index (NDVI) and Normalized Difference Water Index (NDWI) for mapping green infrastructures and water bodies. Air Quality Index (AQI) data from the year 2020 supplements the study, allowing for an investigation into the relationship between air pollution and UHI. The analysis of all datasets employs the Pearson correlation coefficient to ascertain the nature and extent of correlation among UHI and the identified environmental variables.
Results and Discussion:
The findings reveal the persistent prevalence of Urban Heat Island (UHI) during nighttime across all scenarios in Isfahan. However, during daytime hours, the trend shifts, giving rise to cooler zones within the city borders, indicating the emergence of urban cold islands. A noteworthy revelation from the study is the significant exacerbation of UHI attributed to the density of the urban built environment. Intriguingly, air pollution, though exerting a lesser impact on Land Surface Temperature (LST) compared to built density, still plays a role in elevating LST during daylight.
The study underscores the pivotal role of urban green infrastructure and water bodies in mitigating heat islands. Among these elements, green spaces, particularly vegetation, emerge as highly influential, surpassing the cooling effects of both water bodies and polluted air. The seasonal variation in vegetation cover also influences UHI intensity, with reduced vegetative cover in colder, drier seasons contributing to heightened UHI effects. These spatial and temporal dynamics emphasize the intricate balance between UHI and environmental factors, offering valuable insights for decision-makers. Such insights can guide targeted strategies in urban planning and design to address the challenges posed by UHI.
Conclusion:
The study emphasizes the importance of considering UHI in urban planning, design, and sustainability discussions. Strategies include reducing built density and integrating green and blue infrastructures. Addressing air quality and vegetation cover in shaping urban thermal landscapes suggests comprehensive policies. Guarding against UHI through natural space preservation and innovative design solutions tailored to Isfahan's climate can enhance urban livability. Future work should quantify contributions of different elements for comprehensive UHI mitigation models. This Isfahan case study serves as a cornerstone for wider applications across similar cities, aiding in combatting global warming and UHI effectively.
Urban Ecology
Mostafa Karimi; Samaneh Khosnavaz; Aliakbar Shamsipour; Masoumeh Moghbel
Abstract
Today, urban development and air pollution are the most important issues concerning urban climate that can affect the quality of urban life. Despite the significant progress made in the fuel and engine technology, emission of pollutants in urban environments is still prevalent. As in many other countries, ...
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Today, urban development and air pollution are the most important issues concerning urban climate that can affect the quality of urban life. Despite the significant progress made in the fuel and engine technology, emission of pollutants in urban environments is still prevalent. As in many other countries, the environmental issue is particularly evident in the large cities of Iran such as Tehran, Tabriz, Isfahan, Shiraz, Arak, and Karaj. The rapid urbanization, industrialization, and increasing trend in the use of motor vehicles have caused numerous environmental issues, including the production and distribution of different types of air pollutant, especially in Tehran, the capital. Tehran’s confinement by mountains and meteorological factors such as temperature inversion, the persistence of high-pressure systems with cold air, and local winds exacerbate pollution. Hence, numerous studies have been conducted on air pollution in Tehran. The results have indicated that 73% to 85.5% of the air pollution observed at urban stations is caused by temperature inversions, which are influenced by high pressure and surface radiation. According to the above research, the key factors involved in the spread of pollution over the streets besides the spatial and natural factors that can affect the distribution of air pollutants (i.e. geographic location, topography, etc.) include the arrangement of the buildings, particularly in terms of street width and orientation, distance, and intersections. It should be noted given the significance of the issue that the pollution can have extensive effects although it occurs at the street level, due to the interaction of the dispersal and diffusion of pollutants through meteorological conditions (wind speed and direction and atmospheric stability), the configuration of buildings, and the orientation of streets. Therefore, the main purpose of this research was to specify the characteristics of pollutant flow and dispersion on urban passages in micro scale. For that purpose, the meteorological data, including air temperature, relative humidity, and wind speed and direction, were extracted from Iran Meteorological Organization (IMO) Geophysics Weather Station (the closest station to the area under investigation) for a 20-year statistical period (1991-2010). Two areas (1 and 2) in Municipal District 6 were specified as making up the area under study in this research. Then, the pollutant dispersion data were obtained based on the relationship between traffic volume and pollutant production during two winter and summer months (July and January) and at three times of the day (morning, midday, and afternoon). Finally, the distribution of air pollutants was simulated using the ENVI-met microscale model for building configuration and street orientation in the area under investigation. The results demonstrated that street and pathway orientation plays an important role in the accumulation or distribution of pollutants. Accordingly, the density of pollutants is higher in streets that are perpendicular to the prevailing wind direction. Furthermore, the concentration of pollutants in the main streets of the area under study exhibited a significant relationship with their directions. Pollutant concentration was moderate in streets with prevailing north winds, while the highest and lowest amounts of pollutant concentration were observed in streets with south and southwest winds, respectively. It can be concluded that consideration of the climate conditions in urban design and development (wind speed/direction in particular) can be effective in improvement of air quality in urban areas. Air Pollution, Street Orientation, Wind Speed/Direction, Tehran, ENVI-met Model.
