Emergencies do not stop at night: Advanced analysis of displacement based on satellite-derived nighttime light observations

Abstract

Around 68.5 million people are currently forcibly displaced. The implementation and monitoring of international agreements, which are linked to the 2030 agenda (e.g., the Sendai Framework), require a standard set of metrics for internal displacement. Since nationally owned, validated, and credible data are difficult to obtain, new approaches are needed. This article aims to support the monitoring of displacement via satellite-derived observations of nighttime lights (NTL) from NASA's Black Marble product suite along with an short message service (SMS)-based emergency survey after Cyclone Idai had made landfall in Beira, Mozambique, in March 2019. Under certain conditions, the spatial extent of power outages can serve as a proxy for disaster impacts and a potential driver for displacement. Hence, information about anomalies in NTL has the potential to support humanitarian decision-making via estimations of people affected or the coordination of rapid response teams. Despite initial issues related to cloud cover, we find that around 90% of Beira's power grid had been affected. In collaboration with the Internal Displacement Monitoring Center, we use these findings to establish a framework that links NTL observations with existing humanitarian decision-making workflows to complement ground-based survey data and other satellite-derived information, such as flood or damage maps.