Three decades of urban densification reduced winter direct sunlight access across China's old urban cores.

Authors

Kechao Wang, Xiangyuan Wu, Liutao Chen, Tzu-Hsin Karen Chen, Wu Xiao

Published in

Proceedings of the National Academy of Sciences of the United States of America. Volume 123. Issue 40. Pages e2624733123. Oct 06, 2026. Epub Sep 28, 2026.

Abstract

Urban densification is widely promoted to improve land-use efficiency and curb sprawl, but it can reduce winter sunlight in old urban cores, an important dimension of urban livability. Although three-dimensional (3D) urban form is known to shape sunlight availability, most studies focus on present-day conditions, typical urban forms, or planning scenarios. How much sunlight has been lost through recent redevelopment, particularly in legacy neighborhoods, remains unclear. Here we quantify densification-induced winter direct-sunlight loss across the old urban cores of 77 large cities in mainland China. We map winter-solstice direct-sunlight access at 5-m resolution using 3D building data and city-specific solar geometry, comparing the observed 2020 built environment with a counterfactual (CF) circa-1990 height field for legacy buildings. The CF uses city-specific empirical height caps and is evaluated against historically documented block-scale cases. Over three decades, densification reduced sunlight across 36% of old-core areas on average, with mean duration in affected areas declining from 5.37 to 3.75 h. Around 7% of the area (603 km²) shifted from sufficient to insufficient sunlight, while 17.7% (1,525 km²) fell below the 2-h threshold by 2020. Mean losses ranged from 1.08 to 2.46 h across cities, affecting approximately 16 million first-floor residents, including around 0.61 million exposed to severe losses of 3 to 6 h. Losses were more extensive in cities with shorter baseline sunlight, greatest in second-tier cities, and steeper at higher latitudes. These findings provide a scalable basis for sunlight-sensitive urban renewal and height regulation.

PMID:
42804636
Bibliographic data and abstract were imported from PubMed on 29 Sep 2026.

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