Peru has experienced a long history of disasters linked to the El Niño-Southern Oscillation (ENSO), including during the global El Niño events of 1982–83 and 1997–98. This history has contributed to progress in ENSO forecasting and preparation, as well as broader development of the country's disaster risk management (DRM) capacities. Despite such advances, in early 2017 Peru was devastated by a localized “coastal El Niño” event. This study examines why the 2017 event proved so catastrophic, especially given Peru's substantial preparations for the 2015-16 global El Niño a year earlier. To address this question, the analysis applies a disaster forensics approach grounded in the interdisciplinary lens of political ecology. Drawing upon historical and institutional analysis and stakeholder interviews, the study describes how the geophysical characteristics of El Niño events interact with the extensive exposure and vulnerability of Peru's population and infrastructure to produce high levels of disaster risk. The study then examines the contemporary institutional context for DRM in Peru and describes recent measures to address El Niño-related risks specifically. While acknowledging challenges to DRM linked to El Nino's geophysical attributes, the analysis locates crucial root causes of Peru's recent El Niño disasters in socio-political and institutional characteristics—including centralization, sectoral division, and corruption—and describes how these factors undermine efforts to develop more integrated and robust DRM capacities. The analysis concludes with recommendations for conducting forensic studies of the political ecology of disaster in other contexts.