CHARACTERISTICS OF PRECIPITATION SYSTEM IN HIROSHIMA PREFECTURE DURING THE HEAVY RAINFALL EVENT OF JULY 2018 OBSERVED USING XRAIN DATA

Abstract

 Heavy rainfalls with band-shaped precipitation systems poured on the western part of Japan from June 28 to July 8, 2018, causing flooding and sediment disasters over Hiroshima Prefecture. At the same time, the Ministry of Land, Infrastructure and Transport (MLIT) had operated the eXtended RAdar Information Network (XRAIN) consisting of X-band Multi-Parameter (MP) radars and C-band MP radars. This study clarifies the process and mechanism of the heavy rainfalls based on the meteorological conditions calculated using the MesoScale Model (MSM) of the Japan Meteorological Agency (JMA) and the XRAIN data over Hiroshima Prefecture.

 We obtained the following findings. First, compared to rain gauges, XRAIN captured the spatiotemporal distribution of rainfall intensity with high accuracy. Second, three-dimensional rainfall intensity, generated by the Cressman interpolation of two X-band MP radars, allowed us to visualize the evolution of the band-shaped precipitation systems. Third, the cloud top of the band-shaped precipitation system reached an altitude of less than 8, 000 m, which was low compared to the convective heavy rain on August 20, 2014. Finally, the high rainfall intensity recorded near Hiroshima Station at 1805 local standard time (LST) July 6, 2018, was due to the band-shaped precipitation system with sufficient water vapor supply from the south and atmospheric instability.