Mitigating Heat Islands Effect in Mega Cities through Districts' Prioritisation for Urban Green Coverage Applications: Cairo – Egypt as a Case Study

Abstract

Heat-related problems have become a global issue resulted from climate change. Prolonged exposure to extreme high temperatures increased the percentage of mortality and morbidity in cities worldwide. Urbanization and population contribute to urban heat islands effect (UHIE). The purpose of this paper is to prioritize urban areas at high risk for heat related incidents in mega cities and to propose the implementation of urban green coverage (UGC) strategies which contribute to mitigating UHIE. The methodology includes a review on the UHI problems, along with the cooling benefits the UGC can produce. Then, the study's application is mainly focused on Cairo Governorate, Egypt as an example of a developing country. Cairo Governorate, Egypt lacks well maintained vegetation in almost all districts as results indicated that it has a mean normalized difference vegetation index (NDVI) ranging from 0.08 to 0.25. The study adopts the Australian model developed by Norton et al. [Landsc. Urban Plan. 134, 127 (2015)], which includes the intersection of three factors (heat exposure, vulnerability, and behavioural exposure) to identify a high priority area. It was difficult to assess the behaviour of population in outdoor public spaces in a city like Cairo; hence, the study follows “Crichton's Risk Triangle” conducted by Morabito et al. [PLoS One 10, e0127277 (2015)], to identify high risk areas based on the intersection of three layers: (a) high day-time/night-time surface temperatures − hazard; (b) total exposed population in a city − exposure; and (c) sub-populations at risk of being harmed during extreme heat − vulnerability. In the simulation, the risk assessment method simplifies the process of constructing the GIS database as it is composed of layering system. The development of a Heat-related Vulnerability Index (HVI) map for Cairo districts was conducted by over layering the natural hazard layer (land surface temperature) with spatial demographic data using GIS Software. Results of risk maps of Cairo were presented and showed normalized HVI values ranging between 0.0 and 1.0, which can be categorized into five risk levels (very low to very high). Results also indicated that 13 out of the 46 districts in Cairo are at very high/high risk, while only 5 districts have a very low risk. Finally, a tool was established to map the population vulnerability to extreme heat events by identifying high priority risk areas that requires urgent intervention by applying more UGC to mitigate UHIE and climate action and adaptation.