Localized heavy rainfall near Zoshigaya, Tokyo, Japan on 5 August 2008 observed by X-band polarimetric radar - Preliminary analysis

Abstract

Localized heavy rainfall that occurred in the Toshima, Chiyoda, Shinjuku, and Bunkyo wards of Tokyo, Japan on 5 August 2008, causing 5 deaths and the flooding of 34 houses above floor level, was observed by the National Research Institute for Earth Science and Disaster Prevention (NIED) X-band polarimetric radar (MP-X). Preliminary analyses of the radar data reveal the following characteristics of the rainfall event. Heavy rainfall occurred in a small area over a short period. The extents of the areas over which 1-hour accumulated rainfall was greater than 50 and 80 mm were about 20 and 5 km2, respectively. The maximum total rainfall amount (123 mm) from 11:30 to 13:30 LST was observed by MP-X over Edogawa Elementary School. The thunderstorm initially developed rapidly. Only 15 minutes after the onset of rainfall, a precipitation rate in excess of 100 mm h-1 was observed, continuing for 35 minutes from 11:55 to 12:30 LST. The maximum rainfall rate (153 mm h-1) was observed by a raingauge over Edogawa Elementary School at around 12:10 LST. A comparison of MP-X data with surface rain-gauge data reveals that MP-X provides more accurate rainfall information than conventional radar, making it useful in monitoring localized heavy rainfall.