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.