Increased artificial illumination delays urban autumnal foliar senescence

Rapid urbanization has driven widespread increases in artificial light at night, intensifying energy use, light pollution, and sustainability challenges. However, its ecological impacts, particularly on vegetation phenological transitions, remain poorly understood. Using 62,994 site-year in situ records and satellite observations across 452 cities from 2001 to 2022, we show that elevated levels of artificial light at night are associated with delayed dates of foliar senescence in urban areas. This delaying effect is spatially heterogeneous and nonlinear, being most pronounced at low light intensities ( < 15 nW cm^-2 sr^-1) and decreasing or saturating at higher levels. Regional variability in effects of artificial light at night is primarily shaped by urban socioeconomic factors and vegetation traits. Mechanistically, the delaying effect may result from enhanced carbon assimilation and altered climatic responses. We further improve the phenological modeling by incorporating the effects of artificial light at night and project overall later foliar senescence dates than currently predicted. Collectively, our findings highlight a previously underrecognized pathway by which urbanization alters vegetation phenology, with implications for forecasting ecosystem dynamics under continued urban growth and climate change.