Sound exerts wide‐ranging influence on humans. The quality of that influence depends on the sound source and context in which it is perceived, but nature sounds are generally preferred by people and associated with health and well‐being benefits.
In many environments, sounds are highly mixed giving rise to a multi‐source ‘soundscape’ that may vary through days or seasons. The complex and dynamic nature of soundscapes makes them challenging to quantify or classify to rigorously compare them and their contributing sources quantitatively through space and time.
We address this challenge by developing an analytical procedure resulting in a generalized soundscape classification framework that (i) elucidates dominant sound sources (e.g. biophony vs. anthrophony) and (ii) can be used to improve our understanding of spatial and temporal variation in soundscapes across different contexts.
We also address a knowledge gap in urban sound research by describing the soundscapes of urban informal settlements in Fiji and Indonesia. Despite the growing emphasis on improving the physical design and quality of life in urban informal settlements, little is known about soundscapes in these settings or their relationship to human health and well‐being.
We identified seven soundscape classes representing relative dominance by (i) sustained geophony, biophony dominated by (ii) insect stridulation or (iii) bird song, anthrophony dominated by (iv) machines, (v) vehicles, (vi) human voices or (vii) a mixture of the former. These classes were applicable in both Indonesia and Fiji but differed in their prevalence between the countries, times of day and seasons in expected ways. Future automatic sorting of new sound data into this classification framework is provided by a supervised classification model that attained an overall testing accuracy of 94% and Cohen's kappa of 0.93.
Our procedure yields broadly applicable, informative soundscape classes indicative of dominant sound sources, including natural sounds, that are known to have different effects on human health. Therefore, our soundscape classification framework can be used in conjunction with health, well‐being, or economic data, to aid the development, assessment and scaling of sustainable design solutions for liveable cities and especially for improving urban informal settlement environments.
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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 C in long-urbanised parts of the city and 6.3 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.
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