Urban Waters, Unseen: The Hydrology of Informal Settlements Must Not Be Ignored

Informal settlements—home to more than 1 billion people worldwide—remain largely invisible in urban hydrological science. Despite their density, structural complexity, and distinctive water pathways, these neighborhoods are routinely omitted from flood models, drainage assessments, and water‐resource analyses due to data gaps and limitations of conventional mapping and monitoring tools. This omission distorts our understanding of runoff generation, infiltration, storage, and contamination in some of the most hydrologically dynamic parts of cities. Drawing on recent progress in Rio de Janeiro's favelas, where community‐based monitoring, hyper‐resolution topography, and tailored remote sensing are beginning to fill these gaps, this commentary argues that incorporating informal settlements is essential for accurate modeling and equitable environmental risk management. I outline a research agenda for an inclusive urban hydrology that integrates local knowledge, fine‐scale observations, and next‐generation modeling frameworks. Addressing this blind spot is critical for advancing the science of water in rapidly urbanizing and hazard‐vulnerable regions.