Impact-based forecasting in Japan: a review of the Japan meteorological agency’s real-time risk map “Kikikuru”

Abstract Impact‑Based Forecasting (IBF) has attracted international attention as an approach to enhance disaster risk management by linking weather forecast information to concrete societal actions. This review examines the implementation of IBF in Japan, focusing on the Real‑time Risk Map provided by the Japan Meteorological Agency, and systematically organizes its design philosophy, technical structure, operational framework, and role in decision support. Japan is characterized by steep topography and numerous short rivers with steep gradients, under which rain‑related disasters such as landslides, inundation, and flash floods tend to occur rapidly and in a highly localized manner. Under these conditions, the Real‑time Risk Map evaluates disaster risk by transforming precipitation into indices that represent the progression of physical processes such as subsurface infiltration, storage, and runoff, and by combining these indices with criteria that reflect past disaster records and regional characteristics. As a result, risk information with high temporal update frequency and spatial resolution is visualized on maps. Rather than explicitly quantifying hazard, exposure, and vulnerability as separate components, the Real‑time Risk Map is designed as information to support decision‑making, including evacuation judgment, and is operated in coordination with warnings, advisories, and the nationally shared Alert Levels. From an IBF perspective, this review organizes the technical structure and decision‑support functions of the Real‑time Risk Map and clarifies its positioning through comparison with international IBF developments. It further illustrates the role of the Real‑time Risk Map in Japan’s IBF practice through evaluations based on concrete case studies, and discusses remaining challenges, including the treatment of forecast uncertainty.