Correlation analysis of macro-scale natural and built environment factors with urban heat islands intensity: Case Study of Isfahan city

 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.

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.

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.

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.