Nocturnal Surface Urban Heat Island over Greater Cairo: Spatial Morphology, Temporal Trends and Links to Land-Atmosphere Influences

Ahmed M El Kenawy,Sergio M Vicente-Serrano,Sayed M Robaa,Dhais Peña-Angulo,Mohamed Hereher,Noura Al Nasiri,Talal Al-Awadhi,Petra-Manuela Schuwerack,Salim Al-Hatrushi,Ali Al-Buloshi,Juan I Lopez-Moreno,Mohamed M Abdelaal,Fernando Domínguez-Castro,Islam M Gaber,Matthew F Mccabe

doi:10.3390/rs12233889

Abstract

This study assesses the spatial and temporal characteristics of nighttime surface urban heat island (SUHI) effects over Greater Cairo: the largest metropolitan area in Africa. This study employed nighttime land surface temperature (LST) data at 1 km resolution from the Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua sensor for the period 2003–2019. We presented a new spatial anomaly algorithm, which allowed to define SUHI using the most anomalous hotspot and cold spot of LST for each time step over Greater Cairo between 2003 and 2019. Results demonstrate that although there is a significant increase in the spatial extent of SUHI over the past two decades, a significant decrease in the mean and maximum intensities of SUHI was noted. Moreover, we examined the dependency between SUHI characteristics and related factors that influence energy and heat fluxes between atmosphere and land in urban environments (e.g., surface albedo, vegetation cover, climate variability, and land cover/use changes). Results demonstrate that the decrease in the intensity of SUHI was mainly guided by a stronger warming in daytime and nighttime LST in the neighborhood of urban localities. This warming was accompanied by a decrease in surface albedo and diurnal temperature range (DTR) over these areas. Results of this study can provide guidance to local urban planners and decision-makers to adopt more effective mitigation strategies to diminish the negative impacts of urban warming on natural and human environments.

Highlights

The Greater Cairo is the largest metropolitan area in Africa
Our assessment was based on employing Moderate Resolution Imaging Spectroradiometer (MODIS) nighttime land surface temperature (LST) at 1 km spatial resolution and 8-day composites for the 17-year period encompassing January 2003 to December 2019
The decrease in the intensity of surface urban heat island (SUHI) was mainly driven by stronger changes in albedo and daytime and nighttime LSTs over suburban areas, which modulated the intensity over central areas of the city

Summary

Introduction

The Greater Cairo is the largest metropolitan area in Africa. It has witnessed rapid changes in population, urbanization, and extensive economic activities over both space and time, inducing critical impacts on the local environment, carbon cycle, and even climate change [1]. Greater Cairo has witnessed rapid urbanization in the past few decades, with new cities (e.g., 6th October and Al Obour) being born and added to the “traditional” megacity This rapid trend of urbanization is projected to continue in the future, mainly due to demographic forces (e.g., high population growth, continuing internal migration from surrounding less-developed regions) and urban sprawl into agricultural lands. All these natural and human stressors, combined with a possible future acceleration of air temperature and intensification of extreme heat waves, may act to increase the heat load to urban dwellers [4,5,6]

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Conclusion