Microscale Investigation of Urban Heat Island (UHI) in Annaba City: Unveiling Factors and Mitigation Strategies

Abstract

Cities are facing significant challenges related to climate change, particularly due to the increasing impact of the Urban Heat Island (UHI) phenomenon. The present study investigated the UHI phenomenon at the microscale in Annaba, Algeria. The research involved a multi-step approach, starting with on-site measurements of urban microclimate parameters, performed in downtown Annaba on 6 July 2023. The UHI intensity was quantified by comparing city-measured temperatures with rural surroundings. Thermal imaging is then used to empirically identify the contributing factors to UHI initiation at the microscale. The study employed the ENVI-met model to analyse mitigation strategies, manipulating parameters for six scenarios including the current design of the study area. Outputs were used to assess the impact of these strategies on air temperature, mean radiant temperature, relative humidity, and wind speed. The findings revealed an intense UHI effect in Annaba city with a peak difference of 6.9 °C, with practical implications for buildings, ground and roads, vehicles, air conditioners, and specific facade materials. Introducing urban vegetation, particularly urban trees and green roofs, proved highly effectiveness in mitigating the UHI in downtown Annaba. Urban trees demonstrated the most substantial impact, reducing temperatures by 1.9 °C at 1 p.m., while green roof temperature reductions ranged from 0.1 °C to 2 °C.

Nature-based solutions for climate change mitigation: A perspective on challenges, potential and limitations

“…This study underscores the green roofs' potential in cooling urban landscapes, thereby reducing the urban heat island effect and enhancing urban resilience to climate change. Additionally, Sayad et al [16] further validate the effectiveness of green roofs in mitigating urban heat islands, as explored in Annaba City. Their findings highlight significant reductions in surface temperatures, contributing to a more sustainable urban microclimate.…”

“…Green Roofs Climate regulation, biodiversity Sayad et al [16] Investigate urban heat island phenomenon in Annaba city Effectiveness of green roofs in mitigating climate change and urban heat island phenomenon…”

“…A comparative analysis of these studies on NbS to climate change mitigation reveals significant insights into the diverse applications, benefits, and challenges in different contexts. The studies by Quaranta et al [15] , Sayad et al [16] , and Zheng and Chen [17] focus on green roofs, demonstrating their effectiveness in climate regulation, biodiversity promotion, and reducing urban heat islands, particularly in densely populated urban areas like Shanghai and Annaba.…”

Advancing Urban Microclimate Monitoring: The Development of an Environmental Data Measurement Station Using a Low-Tech Approach

“…Ultimately, the discussion of the outdoor thermal comfort of inhabitants over long periods and the calculation of the UHI intensity within a neighborhood or on a larger scale are possible. Another aim of this study is the collection of several meteorological data in an urban context to facilitate the calibration of numerical models [44]. Indeed, deploying this sensor in the network will contribute to establishing large datasets of urban environmental parameters that are crucial for improving numerical models such as Envi-Met [45] or SOLENE-microclimat [46].…”

Analyzing Urban Climatic Shifts in Annaba City: Decadal Trends, Seasonal Variability and Extreme Weather Events

“…The Mediterranean climate is characterized by mild, wet winters and hot, dry summers and has long been a defining feature of Annaba. Despite its classification as possessing a subhumid and moderate climate [38], in recent years, the city has witnessed a discernible departure from this norm, experiencing unprecedented weather phenomena, particularly instances of excessive heat phenomena such as the urban heat island (UHI) effect [39,40]. In tandem with these local disturbances, the World Meteorological Organization (WMO) has been at the forefront of monitoring and analyzing global climate trends, consistently reporting an alarming increase in average global temperatures over the past few decades and specifically in summer 2023, serving as a poignant indicator of global climate change trends [21].…”