Urban densification and urban heat islands in Kigali, Rwanda

Abstract

Kigali is one of the East African cities that has experienced rapid spatial and physiognomic evolution since the 2010s. One of the consequences of this growing urban dynamic is the conversion of natural land to artificial surfaces. This is detrimental to green spaces due to the densification of buildings and increase in asphalt covered surfaces and paved roads, which leads to the development of heat islands. In current studies, the issue of heat islands has become an important environmental and societal issue because of its impact on human health. However, very few studies have been conducted at the scale of African cities to identify and consider this phenomenon in terms of urban planning strategies. The objective of this study is to conduct a geo-historical analysis of the urban expansion of the city of Kigali and its consequences on that evolution of surface temperatures and to identify the neighbourhoods most affected by heat islands. The analysis of urban dynamics is based on the extraction of urban areas from Landsat images acquired in 1984, 2010 and 2021. Surface temperature data were derived from these images. This work is also based on field observations and analysis of archival records. The results reveal that the spatiotemporal evolution of hot surfaces follows the same trajectory as the expansion of the urban area, which extends from the historical centre to the eastern and southern boundaries of the city. Even if Kigali is still considered a green city, due to the presence of many green spaces and some remaining forested areas, some districts, notably the city centre and Remera, are almost devoid of vegetation and appear as heat islands due to the high degree of urbanization. These heat islands could be amplified in the context of current global warming. The identification and monitoring of hot surface areas can be a tool used for urban planning and enacting public health policies, particularly through the creation of cool islands and by i