P35

Characterizing Types of Rainfall Prone to Sediment Disasters and Their Future Change in theRokko Mountain〇Ying-Hsin WU, Yukari NAKA, Eiichi NAKAKITA

BackgroundEstimating the future risk of sediment disasters in aaims to examine the types of all rainfall events andcorresponding rainfall features of maximum rainfallchanging climate has been one of the essential topics

rate, duration, and cumulated amount.

recently. We have attempted to assess the future change

Data and methodof landslide alerts in Japan in a changing climate withIn this study, we analyze two types of datasets,

the application of the critical line method, abbreviatedincluding Radar/Raingauge-Analyzed Precipitationas CL, a hydrometeorological approach that utilizes apublished by JMA, often referred to as Radar-parametric curve comprising hourly precipitation (HR)AMeDAS, with a spatial resolution of 1-km, andand soil-water index (SWI). The two parameters

climate projections simulated by using regional climate

represent the effects of short-term rainfall and long-models NHRCM at the two spatial resolutions of 2-km

term soil wetness respectively. When considering aand 5-km. The data of Radar-AMeDAS covers a period

rainfall event, the geometric range of the correspondingof 17 years (2006-2022) while the climate projections

snake line is significantly influenced by various factors

have 20 years for all members. The climate projections

such as rainfall pattern, including duration, peak

are based on three scenarios, including present climate,intensity, time series, and more. Generally, an increase

RCP2.6, and RCP8.5. For the future climate projections,of in rainfall duration corresponds to a larger SWI value

the member is the ensemble mean of SST, often

SWI, indicating a wider SWI range. On the other hand,referred to as c0. In our analysis of rainfall types, weintensified rainfall leads to a higher HR value, resulting

specifically focus on events in which the CL is crossed.

in a wider range of HR. To quantitatively assess the riskof sediment hazards, one can easily examine the range

Analysis resultsof snake line composed of HR and SWI. Moreover, forThe results depicting rainfall types from various

an objective assessment of the change of snake-line

datasets are illustrated in Fig. 1. In both historical

range, a reliable and established tool is the method ofobservation and the present climate scenarios, theradial-basis function network, often referred to as

predominant rainfall type is associated with the events

RBFN, which has been used for determining critical

related to typhoon comparing to the other types. Twolines (CL). In our recent study (Wu et al., 2024), we

significant differences are observed. The first notableutilized the RBFN method to analyze all rainfall events

contrast with Radar-AMeDAS is that cold fronts fromfrom climate projections under various scenarios and toNHRCM induce rainfall events in which the CL aregenerate RBFN curves at various values corresponding

crossed. The second is that, from 2-km NHRCM, weto occurrence probability. Subsequently, to reveal thecan extract CL-crossed rainfall events occurred in astretching patterns in the directions of SWI and HR, welocalized area, but there is none of the localized rainfall

conducted an examination of the generated RBFN

extracted from NHRCM05. Additionally, according tocurves by comparing among future and present climate

our definition of rainfall types, approximately one-thirdprojections. The results show contrasting stretchingof the events occurred in composite weather systems

patterns two climate projections with different spatial

rather than exclusively in a single system. Finally, for aresolutions. To comprehend this discrepancy, this study

deeper understanding of the discrepancy in rainfallfeatures between the two NHRCM models, acomparison based on rainfall duration and its frequency
as well as cumulated amount are illustrated in Fig. 2.
As a result, it is evident that rainfall events fromNHRCM02 exhibit higher intensity in durations shorter
than 72 hours, with cumulated amounts less than 400mm, but feature a higher maximum hourly rain rate. In
contrast, NHRCM05 shows generally longer rainfall
durations with higher cumulative amounts. Thesefindings offer a clear explanation for the observed
discrepancy in the stretching pattern of snake lines andhazard trends between the two NHRCM models withspatial resolutions of 2 km and 5 km.
Acknowledgement
This research is conducted by Theme 4 of the Advanced
Studies of Climate Change Projection (SENTAN Program)Grant Number JPMXD07226785-34 supported by theMinistry of Education, Culture, Sports, Science andTechnology (MEXT), Japan, and supported by MLIT
research funding as well as JSPS KAKENHI Grant No.
22K04331. The authors appreciate MLIT Sabo Office andprefectural governments for providing the latest criticalline information.
Fig. 1

References
Wu, Y.-H., Yamaji, A., & Nakakita, E. (2024, in press).
Application of radial-basis function network tocharacterize future rainfall prone to sediment hazards
in a change climate, Journal of JSCE Special Issue(Hydraulic Engineering)

Fig. 2

Pie charts depicting types of rainfall events in which
the critical lines are crossed. These events areextracted from Radar-AMeDAS and the scenariosof SPA, RCP2.6, and RCP8.5 from NHRCM05, andNHRCM02.

Comparison of rainfall duration and its relative frequency, as well as cumulated amount among RadarAMeDAS and the scenarios of SPA, RCP2.6, and RCP8.5 of NHRCM02 and NHRCM05