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The interplay of cloud cover and 3D urban structures reduces human access to sunlight

Nature Cities volume 1, pages 686–694 (2024)Cite this article

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Abstract

Sunlight exposure in urban areas is essential for human health, yet its reduction due to cloud cover and complex 3D urban architecture is often overlooked. Here we introduce a framework that combines natural day length variations, cloud cover and 3D urban structures to assess sunlight duration in cities. Applying this framework to 1,353 US cities, we found a significant decrease of 2,896 h (121 days) in available sunlight for 2020, with cloud cover accounting for 2,448 h (102 days) and urban structures contributing to a 448-h (19-day) loss. With the observed increasing trends in cloud cover and urbanization, sunlight loss is likely to worsen. Our study highlights the pressing need for interdisciplinary urban planning strategies that prioritize adequate access to natural sunlight.

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Fig. 1: Conceptual diagram illustrating the determination of sunlight outcomes in 3D urban environments.
Fig. 2: Annual sunlight maps for 1,353 cities in the United States for 2020.
Fig. 3: City-level associations between mean building height and sunshine reduction fraction over the built-up area for 1,353 US cities.
Fig. 4: The trend of cloud cover for 1,353 cities in the contiguous United States observed by three different datasets.

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Data availability

Urban boundary of TIGER vector database is available at https://www.census.gov/tiger-data; WorldCover land cover product is available at https://esa-worldcover.org; GOES-16 clear sky mask product is available at https://www.goes-r.gov/spacesegment/abi.html; MOD09GA cloud mask product is available at https://developers.google.com/earth-engine/datasets/catalog/MODIS_061_MOD09GA; MYD09GA cloud mask product is available at https://developers.google.com/earth-engine/datasets/catalog/MODIS_061_MYD09GA; ISCCP HXG cloud mask product is available at https://gee-community-catalog.org/projects/isccp_hxg/; DSM data are available at https://planetarycomputer.microsoft.com/dataset/3dep-lidar-dsm; PlanetScope satellite data are available at https://www.planet.com/ under Planet Lab’s Education and Research license; NAIP aerial imagery is available at https://developers.google.com/earth-engine/datasets/catalog/USDA_NAIP_DOQQ; US Department of Energy’s BAP is available at https://atlas.eia.gov/datasets/eia::climate-zones-doe-building-america-program/; Daily Surface Weather and Climatological Summaries (Daymet) is available at https://developers.google.com/earth-engine/datasets/catalog/NASA_ORNL_DAYMET_V4.

Code availability

The script of the SVF calculation is available via GitHub at https://github.com/EarthObservation/RVT_py; the software of the natural solar duration time calculation is available at https://gml.noaa.gov/grad/solcalc/sunrise.html.

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Acknowledgements

This study is supported by The University of Hong Kong HKU-100 Scholars Fund (to B.C.), Seed Fund for Strategic Interdisciplinary Research Scheme Fund (to B.C.) and Basic Research (to S.W. and B.C.), the Research Grants Council of Hong Kong Early Career Scheme (HKU27600222 to B.C.) and General Research Fund (HKU17601423 to B.C.), National Key Research and Development Program of China (2022YFB3903703 to B.C.), National Natural Science Foundation of China Young Scientists Fund (42201373 to B.C.), NSFC/RGC Joint Research Scheme (N_HKU722/23 to B.C.), the Croucher Foundation (CAS22902/CAS22HU01 to P.G.), the Major Program of the National Natural Science Foundation of China (42090015 to P.G.), the Research Grants Council of the Hong Kong Special Administration Region (T35/710/20R to C.L.), The University of Hong Kong Faculty of Business and Economics and Shenzhen Research Institutes (SZRI2023-CRF-04 to C.L.) and The University of Hong Kong Start-up Fund for New Professoriate Staff (to J.A.).

Author information

Authors and Affiliations

  1. Future Urbanity and Sustainable Environment (FUSE) Lab, Division of Landscape Architecture, Department of Architecture, Faculty of Architecture, The University of Hong Kong, Hong Kong, China

    Shengbiao Wu & Bin Chen

  2. Urban Systems Institute, The University of Hong Kong, Hong Kong, China

    Bin Chen, Chen Lin & Peng Gong

  3. Institute for Climate and Carbon Neutrality, The University of Hong Kong, Hong Kong, China

    Bin Chen, Jiafu An, Chen Lin & Peng Gong

  4. Department of Real Estate and Construction, Faculty of Architecture, The University of Hong Kong, Hong Kong, China

    Jiafu An

  5. Faculty of Business and Economics, The University of Hong Kong, Hong Kong, China

    Chen Lin

  6. Department of Geography and Department of Earth Sciences, The University of Hong Kong, Hong Kong, China

    Peng Gong

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  1. Shengbiao Wu
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Contributions

B.C. conceived and designed the study. S.W. performed the main data analysis. S.W. and B.C. wrote the paper. J.A., C.L. and P.G. contributed to interpreting the results and reviewed and edited the paper.

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Correspondence to Bin Chen.

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Nature Cities thanks Marianne Berwick, Valerio Lo Verso, Richard Weller and Hesan Ziar for their contribution to the peer review of this work.

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Wu, S., Chen, B., An, J. et al. The interplay of cloud cover and 3D urban structures reduces human access to sunlight. Nat Cities 1, 686–694 (2024). https://doi.org/10.1038/s44284-024-00120-x

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