Spatio-temporal development of the urban heat island in a socioeconomically diverse tropical city

Abstract

Urban heat islands, where temperatures are elevated relative to non-urban surrounds, are near-ubiquitous in cities globally. Yet, the magnitude and form of urban heat islands in the tropics, where heat has a large morbidity and mortality burden, is less well understood, especially for socioeconomically diverse communities such as those living in urban informal settlements. We utilised 29 years of Landsat satellite-derived surface temperature, corroborated by in situ measurements, to provide a detailed spatial and temporal assessment of urban heat islands in Makassar, Indonesia, a city that is representative of rapidly growing urban settlements across the tropics. We did so with explicit consideration of vulnerable communities living informally. Our analysis identified surface urban heat islands of up to 9.2 {degrees}C in long-urbanised parts of the city and 6.3 {degrees}C in informal settlements, the seasonal patterns of which were driven by change in non-urban areas rather than in urban areas themselves. In recently urbanised areas, the majority of urban heat island increase occurred before areas became 50% urbanised. As tropical cities continue to expand we expect that urban heat islands will develop quickly as land is urbanised, whereas the established heat island in long-urbanised areas will remain stable in response to city expansion. Green and blue space protect some informal settlements from the worst urban heat islands and maintenance of such space will be essential to mitigate the growing heat burden from urban expansion and anthropogenic climate change. We advocate for green space to be prioritised in urban planning, redevelopment and informal settlement upgrading programs, with consideration of the unique environmental and socioeconomic context of tropical cities. HighlightsO_LILong-term, fine-scale data are essential to understand the dynamics of urban heat C_LIO_LISurface heat islands reached 9.2 {degrees}C in the urban core, 6.3 {degrees}C in informal settlements C_LIO_LIIn situ data support the use of remote sensing for heat island characterisation C_LIO_LIThe majority of heat island growth occurred before land was 50% urbanised C_LIO_LIGreen and blue space can mitigate heat in informal settlements C_LI