# Nighttime light dynamics reveal peri-urban brightening and population decoupling in the Chengdu Chongqing megaregion

## TL;DR

Nighttime light data shows rapid urban brightening around Chengdu and Chongqing, with lighting growth outpacing population decline.

## Contribution

The study reveals a 78% rise in nighttime light radiance and a 40% brighter peri-urban 'neon ring' in Chengdu–Chongqing, highlighting policy impacts and population-light decoupling.

## Key findings

- Peri-urban areas brightened 40% more than city cores due to cropland conversion to high-rise housing and logistics estates.
- Local policies like LED retrofits and façade-lighting curfews created persistent 'dark hollows' in downtown areas.
- Luminous sprawl is projected to expand by ~1,000 km² by 2042 despite a 1.6% population decline.

## Abstract

Night-time light (NTL) composites offer a unique spatiotemporal view of urban growth by capturing electricity consumption, infrastructure density, and economic activity patterns that traditional land-cover surveys cannot fully reveal, yet inland China’s megaregions remain understudied from this perspective. Using a 23-year (2000–2022) cross-calibrated NTL product integrated with land-cover, population, and topographic data, we analysed illumination dynamics in the Chengdu–Chongqing economic circle. Mean radiance rose by 78% while the lit area expanded from 0.53% to almost 12%. About three-quarters of this growth is confined to a 4–6 km peri-urban “neon ring” created chiefly by cropland conversion to high-rise housing and logistics estates, now ~ 40% brighter than historic cores. Targeted LED retrofits and façade-lighting curfews produced persistent downtown “dark hollows”, proving that local policy can dampen sky-glow. Cropland-to-urban parcels emitted roughly 6 nW cm⁻² sr⁻¹ more light than other transitions, and protected wetlands brightened threefold, flagging covert development. Spatial autocorrelation analysis revealed extremely high global Moran’s I values (> 0.92 after 2013), indicating strong spatial clustering patterns of illumination changes, with local LISA analysis identifying hotspots predominantly concentrated in the core areas of both cities. Projections indicate ~ 1,000 km² of additional luminous sprawl by 2042 as radiance continues to climb despite a 1.6% population decline, underscoring a widening decoupling between light and headcount.

The online version contains supplementary material available at 10.1038/s41598-025-34706-9.