Heatwave increases nighttime light intensity in hyperdense cities of the Global South: a double machine learning study

Heatwaves, intensified by climate change and rapid urbanization, pose significant threats to urban systems, particularly in the Global South, where adaptive capacity is constrained. This study investigates the relationship between heatwaves and nighttime light (NTL) radiance, a proxy of nighttime economic activity, in four hyperdense cities: Delhi, Guangzhou, Cairo and São Paulo. We hypothesized that heatwaves increase nighttime activity. Using a double machine learning (DML) framework, we analysed data from 2013 to 2019 to quantify the impact of heatwaves on NTL while controlling for local climatic confounders. The results show a statistically significant increase in NTL radiance for Guangzhou, Cairo and São Paulo when a heatwave event lasts at least 2 days, indicating a rise in nighttime activities. However, when we extend the definition of the heatwave beyond the 2-day threshold, such an increase in the NTL values is reduced. We derive insights to improve resilience to the nighttime effects of heatwaves in urban areas.This article is part of the theme issue 'Urban heat spreading above and below ground'.