Analysis of nighttime lights over the cities of Cape Town, Durban and Johannesburg, South Africa

Abstract

Remote sensing of nighttime light (NTL) offers a unique and practical means of assessing human developments through snapshots of nocturnal lighting captured from space. The Visible Infrared Imaging Radiometer Suite (VIIRS) Day/Night Band (DNB) is one of the widely used NTL products and is now publicly available on Google Earth Engine (GEE), which allows accelerated analysis using different geospatial approaches. Here, we perform a comparative trajectory analysis of NTL over the three largest cities of South Africa between 2014 and 2023, and project the changes for 2027 based on Markov chain analysis. Our results show that the NTL increased steadily for the city of Durban (from 27.93 nW cm⁻².sr⁻¹ in 2014 to 29.45 nW cm⁻².sr⁻¹ in 2023) but decreased in the cities of Cape Town (from 32.30 nW cm⁻².sr⁻¹ in 2014 to 31.14 nW cm⁻².sr⁻¹ in 2023) and Johannesburg (from 52.19 nW cm⁻².sr⁻¹ in 2014 to 46.82 nW cm⁻².sr⁻¹ in 2023). The unstable power supply of South African cities can affect the NTL data. In addition, from our results, a similar pattern for each of these cities is observed to be in line with load shedding events in the country, especially for Cape Town and Johannesburg. Regarding the spatiotemporal distribution of the NTL, the central areas have medium to high radiance and have been spreading to the periphery of the cities since 2014. Moreover, land use and land cover (LULC) analysis reveals that developed urban areas, shown by dense built-up areas, coincide with the locations of medium and high NTL radiances. The assessment of NTL changes across low, medium, and high classes indicates a stable configuration with no large changes between classes; this is also observed on the spatial projection of NTL for the year 2027. Our results shed light on NTL mapping in large cities, an area that is constantly evolving due to new developments in remote sensing.