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

Ramsay, E., Duffy, G., Burge, K., et al, 2022, Environmental Pollution

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

The case for nature-based solutions to keep cities cool.

The city of Makassar in Indonesia has nearly tripled in size over the past 30 years. This growth has been accompanied by the expansion of urban heat islands - where a city experiences much warmer temperatures than nearby rural areas. While urbanisation shows no signs of slowing, PhD researcher Emma Ramsay and colleagues at Monash University’s Faculty of Science are investigating how urban heat can be mitigated.

‘Across the city of Makassar, informal settlements are exposed to large urban heat islands. And ongoing expansion of informal settlements will only exacerbate hot and humid conditions in these communities,’ Ramsay explains. ‘But informal settlements are rarely considered in urban heat island analyses, partly due to a lack of spatial data. Weather stations are also often located on the outskirts of cities, making it difficult to compare data from urban and non-urban locations.

‘Our research sets out to explore past trends of urbanisation so that we might understand how urban heat islands could continue to develop with ongoing urbanisation and climate change’.

The research uses 30 years of NASA Landsat satellite imagery going back to the 1990s. This allowed the team to ‘look back in time’ and track urbanisation and the accompanying urban heat islands over the past three decades. Satellite data also helped provide a continuous picture across space. Local temperature monitoring in RISE informal settlements corroborated the remote-sensing approach, showing that the surface temperature is, in fact, representative of conditions that people experience on the ground.

‘We know that heat stress is chronic in the RISE informal settlements, and that residents have little capacity to adapt,’ Ramsay says. ‘And while informal settlements are exposed to large urban heat islands, we found that thanks to their proximity to green and blue space, they are protected from the worst heat in the urban core’.

Characterising the magnitude and spatio-temporal patterns of urban heat islands in informal settlements is essential. The findings highlight the importance of maintaining green space in cities through sustainable urban design to mitigate the health and economic burdens of heat exposure. Ramsay says, ‘Nature-based solutions, such as those being trialled by RISE, represent a solution to maintaining this green and blue space in communities, while delivering much-needed water and sanitation services’.

Cover image: Urban growth in Makassar, Indonesia, from remote-sensed satellite data.