Our new paper, “Worldwide scaling of waste generation in urban systems“, is published in Nature Cities.

The paper and its supporting information can be downloaded at https://www.nature.com/articles/s44284-023-00021-5. Data collected and compiled in this study are available in the figshare repository: https://doi.org/10.6084/m9.figshare.19361675.

Authors: Mingzhen Lu, Chuanbin Zhou, Chenghao Wang, Robert B. Jackson, Christopher P. Kempes

Abstract: The production of waste as a consequence of human activities is one of the most fundamental challenges facing our society and global ecological systems. Waste generation is rapidly increasing, with corresponding shifts in the structure of our societies, where almost all nations are moving from rural agrarian societies to urban and technological ones. However, the connections between these societal shifts and waste generation have not yet been described. In this study we applied scaling theory to establish a new understanding of waste in urban systems and identified universal scaling laws of waste generation across diverse urban systems worldwide for three forms of waste: wastewater, municipal solid waste, and greenhouse gases. We found that wastewater generation scales superlinearly, municipal solid waste scales linearly, and greenhouse gas emissions scale sublinearly with city size. In specific cases, production can be understood in terms of city size coupled with financial and natural resources. For example, wastewater generation can be understood in terms of the increased economic activity of larger cities, and the deviations from the scaling relationship, indicating relative efficiency, depend on gross domestic product per person and local rainfall. The temporal evolution of these scaling relationships reveals a loss of economies of scale and a general increase in waste production, where sublinear scaling relationships become linear. Our findings suggest general mechanisms controlling waste generation across diverse cities and global urban systems. Our approach offers a systematic framework to uncover these underlying mechanisms that might be key to reducing waste and pursuing a more sustainable future.

DOI: https://doi.org/10.1038/s44284-023-00021-5

Fig. 1. Scaling law of waste production across cities worldwide. a, Geolocation of the cities included in this study from three distinct data sources. MoHURD, Ministry of Housing and Urban Rural Development (China). The map was generated using R with the ‘ggplot2’ package. b, Wastewater production scales superlinearly with the size of cities (β = 1.15 ± 0.04, n = 675). We highlight two example cities (black circles) that stand out with a large deviation from the scaling law. Dongguan, an industrial city of southern China that features high personal wealth and high annual precipitation, generates disproportionately more wastewater than expected given its size. In contrast, the northwestern city of Tianshui, which features much lower personal wealth and rainfall, generates much less wastewater than expected given its size. c, MSW production scales linearly with city size (β = 1.04 ± 0.05, n = 292). We highlight Seattle (United States) and Lilongwe (Malawi) as two cities that deviate from the general scaling relationship. The much richer Seattle produces eight times more municipal waste than Lilongwe, even though it has a smaller population. d, The emission of GHGs displays sublinear scaling across cities worldwide (β = 0.85 ± 0.1, n = 296). We highlight Rotterdam (the Netherlands) and Bandung (Indonesia) as two cities that deviate from the general scaling relationship, with Rotterdam producing disproportionately more GHGs. The purpose of highlighting certain high- and low-residual cities is to give concrete examples so that readers can relate to the abstract data points presented here (no subjective judgements are made here). The dark gray error bands in bd represent the CIs of each scaling relationship.