Characteristics of Quasi-stationary Band-shaped Precipitation in the Tohoku Region Detected under Varying Rainfall Thresholds

Abstract

Abstract Quasi-stationary band-shaped precipitation systems sometimes cause severe rainfall disasters in the Tohoku region of northeastern Japan, but the uniform rainfall thresholds used in existing objective detection methods may be too high for this region. This study examines how the detected sample changes when the rainfall thresholds are relaxed, using radar/raingauge-analyzed precipitation amounts for April--October 2000--2024. Relaxing the thresholds substantially increased the number of detected events and newly identified several damaging events missed under the original setting. However, the relaxed settings did not simply add weaker events: some events detected under the original setting were no longer retained because expanded precipitation areas failed some criteria. Regional distribution and orientation were broadly robust across thresholds, whereas event duration and area increased. Composite analyses using a regional reanalysis suggest that newly detected events tended to occur with weaker low-level moisture inflow and weaker low-pressure disturbances.