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Regulation of humid heat by urban green space across a climate wetness gradient

Nature Cities volume 1, pages 871–879 (2024)Cite this article

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Abstract

Green spaces are a common strategy for adaptation to urban warming. Whereas they have been demonstrated to reduce air temperature, much less is known about their effect on air humidity. Because human heat stress is contributed by both temperature and humidity, it is important to quantify the relationship between the effects of both. Here, using mobile measurements in 15 cities, we show that the daytime temperature effect is negatively correlated with the humidity effect, resulting in an insignificant change in the wet-bulb temperature Tw or humid heat (daytime Tw difference between green space and built-up area ΔTw = −0.01 °C). A net reduction in humid heat was observed at night in intermediate (summer precipitation 180 to 570 mm) and wet climates (summer precipitation > 570 mm; mean ΔTw = −0.35 °C). A model simulation revealed that the nighttime Tw reduction resulted mostly from reduction in soil heat storage in vegetated land. These nuanced microclimate responses to urban vegetation caution against a one-size-fits-all solution to climate adaptation.

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Fig. 1: Effects of urban green space on air temperature, humidity and wet-bulb temperature in intermediate-wetness climate.
Fig. 2: Daytime microclimatic effects of urban green space across the climate wetness gradient.
Fig. 3: Relationship between temperature and humidity effects of urban green space.
Fig. 4: Attribution of vegetation effect on the wet-bulb temperature Tw.

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Data availability

The satellite NDVI data are available at https://scihub.copernicus.eu/dhus/#/home. The global land cover data (FROM-GLC) are available at http://data.starcloud.pcl.ac.cn. ESA Worldwide Land Cover Mapping data are from https://esa-worldcover.org/en. Global Local Climate Zone maps can be downloaded from https://www.wudapt.org/. Precipitation assessment uses ERA-5 reanalysis data product, available at https://cds.climate.copernicus.eu/cdsapp#!/dataset/reanalysis-era5-land?tab=overview. TreeMap database is available at https://apps.fs.usda.gov/lcms-viewer/treemap.html. The mobile microclimate data are available via figshare at https://doi.org/10.6084/m9.figshare.27165168 (ref. 51). Imagery data for green space and built-up neighborhood delineation are available via figshare at https://doi.org/10.6084/m9.figshare.26533303 (ref. 52).

Code availability

The MATLAB code used to produce the figures in this paper is available via figshare at https://doi.org/10.6084/m9.figshare.27165168 (ref. 53).

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Acknowledgements

C.C. acknowledges support by the National Natural Science Foundation of China (grant 42005143), X.L. by Robert Wood Johnson Foundation (grant 77476) and a Leitner Award for Uncommon Environmental Collaborations, and Y.Y. and K.Z. by a Yale Graduate Fellowship. We thank the following individuals for their effort in testing the mobile measurement system: M. Bradford, S. Smiley Smith, A. Adams, P. Aldinger, I. Boneh, Z. Chen, D. Chenoweth, J. Chia, H. Darrin, S. Donovan, E. Fine, B. Gilmore, M. Grenon, R. Harlig, A. Hofmann, J. Hofmann, C. Humphrey, D. Kane, Z. Li, C. Sanchez de Lozada, J. Lu, J. Macrone, C. Murphy-Dunning, A. Orloff, K. Pofahl, A. Raffeld, Z. Ratner, M. Reback, P. Rink, K. Shennum, V. Sorab, E. Stagg, U. Talaty, S. Verma, J. Walczak, A. Warner, E. Witts, N. Yeoh, M. Zhong and K. Zimmerman.

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Authors and Affiliations

  1. School of the Environment, Yale University, New Haven, CT, USA

    Yichen Yang, Keer Zhang & Xuhui Lee

  2. Yale-NUIST Center on Atmospheric Environment, International Joint Laboratory on Climate and Environment Change (ILCEC), Nanjing University of Information Science and Technology, Nanjing, China

    Chang Cao

  3. Key Laboratory of Meteorological Disaster, Ministry of Education and Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters, Nanjing University of Information Science and Technology, Nanjing, China

    Chang Cao

  4. Research and Development, Campbell Scientific, Logan, UT, USA

    Ivan Bogoev

  5. Yale College, Yale University, New Haven, CT, USA

    Cosima Deetman, Grace Dietz, Logan Howard, Justin Lai, Hainan Lam & Christopher Yoo

  6. School of Atmospheric Sciences, Sun Yat-sen University and Southern Marine Science and Engineering Guangdong Laboratory, Zhuhai, China

    Jian Hang

  7. Department of Civil and Environmental Engineering, Princeton University, Princeton, NJ, USA

    Xinjie Huang

  8. Brigham Young University, Provo, UT, USA

    Nicholas Kendall

  9. Institute of the Environment and Sustainability, University of California, Los Angeles, Los Angeles, CA, USA

    Kristen Tam

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Contributions

X.L. designed the research. Y.Y. performed data analysis. C.C. assessed the quality of instruments. Y.Y., C.C., I.B., C.D., G.D., J.H., L.H., X.H., N.K., J.L., H.L., K.T., C.Y. and K.Z. contributed to data collection. X.L. and Y.Y. drafted the paper.

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Correspondence to Xuhui Lee.

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Nature Cities thanks Ioannis Kousis, Kerry Nice and Mohammad Rahman for their contribution to the peer review of this work.

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Yang, Y., Cao, C., Bogoev, I. et al. Regulation of humid heat by urban green space across a climate wetness gradient. Nat Cities 1, 871–879 (2024). https://doi.org/10.1038/s44284-024-00157-y

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