Man-Made or Natural: Deciphering the Complex Factors Behind the 2023 Derna FloodDisaster

On September 10, 2023, the city of Derna in northeastern Libya experienced one of the deadliest flood disasters in Mediterranean and African history. Storm Daniel delivered unprecedented rainfall, with Al-Bayda recording 414 mm and Derna receiving over 100 mm within 24 hours, approximately 270 times the region's typical September average of 1.5 mm. This study employs Synthetic Aperture Radar (SAR) from Sentinel and high-resolution Planet imagery to provide a comprehensive analysis of the flood's spatial extent, infrastructure damage, and the interplay between natural and anthropogenic factors that amplified this disaster.

Our flood extent mapping reveals catastrophic impacts on urban infrastructure. The river channel expanded dramatically from 50 meters to approximately 500 meters in width, while the maximum inundated area extended 1.2 km² from the collapsed dams to the Mediterranean Sea over a distance of 2.5 km. The analysis identifies critical damage to infrastructure including the collapse of two upstream dams, destruction of five road flyovers, and significant damage to ports, bridges, and residential areas.

The disaster's severity was substantially amplified by anthropogenic factors. Historical urban development had rerouted the river through artificial canals, with roads and settlements subsequently constructed on the natural riverbed. The two dams, built in the 1970s and unmaintained since 2002, catastrophically failed, releasing an estimated 30 million cubic meters of water. Mann-Kendall trend analysis of 122-year climatic records reveals a statistically significant warming trend (p ≈ 0, Sen's slope = 0.00798) alongside decreasing overall precipitation (p = 0.027, Sen's slope = -0.0389), suggesting a paradoxical pattern where less frequent but more intense rainfall events are becoming more likely.

The socio-economic impacts were devastating, with nearly 4,000 confirmed fatalities in Derna alone, over 10,000 missing, and economic losses estimated at $80 million. Our findings underscore the critical vulnerability created when urban expansion encroaches upon natural floodplains without adequate infrastructure resilience.

This study demonstrates the power of multi-source satellite remote sensing for rapid disaster assessment and highlights the urgent need for integrated flood risk management that considers both climatic extremes and anthropogenic modifications to natural water systems. The lessons from Derna have profound implications for urban planning, dam safety protocols, and climate adaptation strategies in vulnerable Mediterranean regions facing increasingly extreme weather events.