Urban Ecology
fatemeh ghorbanileylestani,; Hassan sajadzadeh
Abstract
HighlightsComprehensive Analysis: This study investigates the Land Surface Temperature (LST) and Normalized Difference Vegetation Index (NDVI) over two decades (2000-2021) in Karaj, highlighting key trends.Correlation Between Vegetation and Temperature: NDVI shows a strong negative correlation with LST, ...
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HighlightsComprehensive Analysis: This study investigates the Land Surface Temperature (LST) and Normalized Difference Vegetation Index (NDVI) over two decades (2000-2021) in Karaj, highlighting key trends.Correlation Between Vegetation and Temperature: NDVI shows a strong negative correlation with LST, indicating vegetation’s cooling impact.Built-Up Areas vs. Green Spaces: High-density urban areas exhibit elevated temperatures, while regions with dense vegetation are noticeably cooler.Key Findings: The primary drivers behind Karaj’s Urban Heat Island (UHI) effect are the reduction of green spaces and the rise in urban land use. IntroductionWith rapid population growth, urbanization is transforming landscapes, often at the expense of natural green areas. Cities are expanding at unprecedented rates, bringing changes in land use, infrastructure, and building density. Natural permeable surfaces, such as vegetation and open spaces, are replaced by impermeable concrete structures that absorb and retain heat, leading to urban microclimate shifts.This transformation has profound environmental impacts. One of the most concerning consequences is the Urban Heat Island (UHI) effect, where urban areas exhibit higher temperatures compared to their rural counterparts. The UHI effect intensifies as cities grow, impacting energy consumption, air quality, and public health. In this context, reducing UHI has become a priority for sustainable urban planning. Cooling strategies—especially the integration of vegetation—are essential to enhance urban resilience, adapt to climate change, and improve quality of life for city dwellers.Materials and MethodsRemote sensing technology was used in this study as a powerful tool for analyzing urban temperature dynamics and land-use changes. Using Landsat satellite images from 2001 to 2021, we examined LST and NDVI for Karaj. Landsat imagery, with a resolution of 30 meters, was sourced from the USGS database. To ensure consistency, cloud-free images were selected from warm-season months for each year.Data processing involved the extraction of LST and NDVI values for Karaj’s administrative boundaries. The satellite images were preprocessed, and land-use classification was carried out using the maximum likelihood approach, categorizing land into three classes: built-up areas, vegetation, and barren land. This classification provided a foundation for assessing the relationship between LST and vegetation cover.Through correlation and regression tree models, we analyzed the interplay between LST and NDVI. By examining changes in both indices, we aimed to understand vegetation’s role in moderating urban heat in Karaj. Our two main objectives were to (1) assess LST and NDVI variations over time, and (2) explore their interdependencies to determine vegetation's influence on UHI.Discussion of ResultsThe analysis reveals a clear trend of rising temperatures across Karaj over the study period. This temperature increase is strongly associated with urban expansion and the decline of natural vegetation. Our findings highlight that land-use type significantly influences LST, with barren and built-up areas having markedly higher temperatures.Central Karaj, a dense urban area with heavy infrastructure and traffic, recorded the highest surface temperatures. These “hot spots” are concentrated around industrial areas, transportation hubs (airports, metro stations, highways), and zones with minimal vegetation. In contrast, areas with vegetation, such as parks and green belts, exhibited substantially cooler surface temperatures. This difference underscores vegetation’s role in absorbing less heat and promoting natural cooling.The spatial distribution of LST shows the hottest zones in arid lands surrounding the city and densely built-up urban areas. The NDVI data further supports this observation; as NDVI values increase, LST values decline, illustrating a negative correlation between vegetation density and surface temperature. The correlation analysis reveals that regions with higher NDVI values, particularly in the eastern and northeastern parts of Karaj, experienced significantly lower temperatures.The land-use maps demonstrate a significant reduction in barren and vegetated areas, accompanied by an increase in urbanized land. These patterns point to a direct relationship between declining vegetation and rising temperatures, reinforcing the critical need for green spaces in Karaj to mitigate UHI effects. Vegetation, as indicated by NDVI, plays a significant role in temperature regulation, with green areas acting as cooling zones in an increasingly built-up landscape.ConclusionsThis study underscores the pivotal role of vegetation in controlling urban temperatures in Karaj. Through detailed LST and NDVI analyses, the results confirm that vegetation coverage is inversely related to LST, with green spaces helping to mitigate the UHI effect. In contrast, barren lands and dense built-up areas contribute significantly to higher temperatures, highlighting the thermal impact of urban development without adequate vegetation.To address the UHI issue, urban planners and policymakers should prioritize sustainable solutions such as increasing green spaces, incorporating green roofs, and developing urban vegetation initiatives tailored to Karaj’s climate. These approaches not only lower urban temperatures but also enhance the city’s environmental resilience, support biodiversity, and improve the overall quality of urban life.Based on the findings, Karaj’s urban planning efforts should focus on preserving existing vegetation and expanding green infrastructure. Effective land-use policies that integrate vegetation can help counteract the adverse effects of rising temperatures, contributing to a more sustainable and livable urban environment.
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.
