Megumi Okazaki, Eiichi Nakakita, Satoru Oishi, Kosei Yamaguchi
Received 18 July, 2025
Accepted 10 September, 2025
Published online 5 December, 2025

Megumi Okazaki¹⁾, Eiichi Nakakita²⁾, Satoru Oishi³⁾, Kosei Yamaguchi⁴⁾

1) Graduate School of Engineering, Kyoto University, Japan
2) Kyoto University, Japan
3) Research Centre for Urban Safety and Security, Kobe University, Japan
4) Disaster Prevention Research Institute, Kyoto University, Japan

Bimodal raindrop size distributions (RDSD) cannot be adequately represented by conventional exponential or gamma distributions. This could affect quantitative precipitation estimation (QPE) using meteorological radars. In this study, we developed a QPE method using a gamma raindrop distribution combined with an exponential (GRACE) distribution, which can represent bimodal RDSDs, and examined its utility. R−K_DP was calculated using the parameters obtained by fitting the GRACE distribution to the RDSD observed using a two-dimensional video disdrometer (2DVD). Estimates based on the GRACE distribution provided results closer to the precipitation intensity observed by rain gauges than estimates based on the gamma distribution or the estimation method used in the extended radar information network (XRAIN), especially during heavy rainfall. The utility of the GRACE distribution for QPE has been clarified; however, it is necessary to investigate the optimal estimation method for various types of rainfall.

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