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Anthropogenic emissions and urbanization increase risk of compound hot extremes in cities

Abstract

Urban areas are experiencing strongly increasing hot temperature extremes. However, these urban heat events have seldom been the focus of traditional detection and attribution analysis designed for regional to global changes. Here we show that compound (day–night sustained) hot extremes are more dangerous than solely daytime or nighttime heat, especially to female and older urban residents. Urban compound hot extremes across eastern China have increased by 1.76 days per decade from 1961 to 2014 with fingerprints of urban expansion and anthropogenic emissions detected by a stepwise detection and attribution method. Their attributable fractions are estimated as 0.51 (urbanization), 1.63 (greenhouse gases) and −0.54 (other anthropogenic forcings) days per decade. Future emissions and urbanization would make these compound events two to five times more frequent (2090s versus 2010s), leading to a threefold-to-sixfold growth in urban population exposure. Our findings call for tailored adaptation planning against rapidly growing health threats from compound heat in cities.

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Fig. 1: Cumulative RR of mortality associated with three types of summertime hot extreme with one-day lag considered.
Fig. 2: Urban- and rural-mean frequency anomalies of summertime compound hot extremes in observations and simulations over eastern China.
Fig. 3: Detection and attribution of frequency changes in summertime compound hot extremes in eastern China.
Fig. 4: Projected changes in frequency of urban compound hot extremes and urban population exposure.

Data availability

All the data that support the findings are publicly available. The temperature observations and LULC maps are available at http://data.cma.cn/en/ and https://www.resdc.cn/Datalist1.aspx?FieldTyepID=1,3 (website available only in Chinese), respectively. The CMIP5 and CMIP6 model outputs can be accessed at https://esgf-node.llnl.gov/projects/cmip5/ and https://esgf-node.llnl.gov/projects/cmip6/, respectively. The global projections of future population and urban expansion based on the SSPs are available at https://sedac.ciesin.columbia.edu/data/set/popdynamics-1-8th-pop-base-year-projection-ssp-2000-2100-rev01 and https://doi.pangaea.de/10.1594/PANGAEA.905890, respectively. The mortality data can be secured through a government data-sharing portal (https://www.phsciencedata.cn/Share/en/index.jsp), from the provincial mortality-surveillance system on registration or from the corresponding author W.M.

Code availability

All the codes associated with this paper are available from the corresponding authors upon reasonable request.

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Acknowledgements

We thank the National Meteorological Information Centre of the China Meteorological Administration for compiling the observational climatic data and we appreciate the Data Center for Resources and Environmental Sciences of the Chinese Academy of Sciences for developing the temporally evolving LULC maps. We acknowledge the World Climate Research Programme’s Working Group on Coupled Modelling, which coordinated and promoted CMIP5 and CMIP6, and we thank the climate modelling groups for producing and making available their model outputs. We thank B. Jones and B. C. O’Neill for developing the spatially explicit global population projections. We also thank G. Chen, X. Li and X. Liu for sharing the global projections of future urban land expansion. J.W., Y.C., Z.Y. and P.Z. were supported jointly by the National Key Research and Development Programme of China (Grant No. 2018YFC1507700) and the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDA20020201). G.H., W.M. and C.H. were jointly supported by the National Nature Science Foundation of China (Grant No. 42075173) and National Key Research and Development Programme of China (Grant No. 2018YFA0606200). S.F.B.T. was funded by the UK-China Research and Innovation Partnership Fund through the Met Office of Climate Science for Service Partnership China as part of the Newton Fund.

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Y.C., J.W., G.H., S.F.B.T. and W.M. designed the research; J.W., W.L., G.H. and Y.C. performed the analyses; J.W. wrote the draft, and Y.C., J.W. and S.F.B.T. reviewed and edited it; S.F.B.T., Z.Y., P.Z., J.F., W.M., C.H. and Y.H. gave valuable suggestions on the analyses; all authors contributed to the interpretation of the results.

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Correspondence to Yang Chen or Wenjun Ma.

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The authors declare no competing interests.

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Peer review information Nature Climate Change thanks Prathap Ramamurthy, Ting Sun and Robbie Parks for their contribution to the peer review of this work.

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Supplementary Note 1, Discussions 1–3, Figs. 1–14 and Tables 1–5.

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Wang, J., Chen, Y., Liao, W. et al. Anthropogenic emissions and urbanization increase risk of compound hot extremes in cities. Nat. Clim. Chang. 11, 1084–1089 (2021). https://doi.org/10.1038/s41558-021-01196-2

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