Temporal Characteristics of Rainfall Events at Very High Timescale

Characteristics of rainfall events and its spell durations are the most important information for natural disasters such as floods, coastal erosion, landslides, water hazards etc. In the present study, we investigated the probability distributions of spell durations for rain exceeding various thresholds (0.5, 1, 2mm/10min) and discussed the peak intensity events (2, 5, 10, 20mm/10min) associated with the rain spell durations from very high timescale (10min) observations at 1296 AMeDAS stations across Japan. Our results infer that the heavy rainfall events (>2mm/10min) over Japan last for shorter duration (up to 1.5hr) and the light rainfall events (<1mm/10min) last for longer duration (up to 2hr). The low intensity events with 2mm/10min peak are found to be short-lived and last up to 3 hours, while the high peak intensity events of more than 5mm/10min are long-lived and last up to 10 hours. The analysis of longer spell wet events (last for at least 12 hours) indicates that the ~15hrs spell duration with 2-10mm/10min peak intensity events occurs more frequently than longer duration event. The very high peak intensity events (up to 10-20mm/10min) are noticed to last up to 24-33hours. These results suggest that the intensity and duration of rainfall events in Japan may play an important role in natural hazards.