Flooding in Oda River Basin during Torrential Rainfall Event in July 2018

Extreme rainfall events cause severe flooding and/or landslides almost every summer in Japan. It seems that the frequency of such events and induced human/economic losses has increased in recent years. A torrential rainfall event in early July 2018 caused severe flooding in many river basins over Hiroshima and Okayama Prefectures of western Japan and resulted a number of fatalities and serious damage to property. One of them is the Oda river basin (about 498 km2), which was severely affected by the flood during the event. Different types of observation systems were used to measure or estimate rainfall for this event. Comparison of radar and satellite-based rainfall shows a good agreement with the rain gauge observations of the entire period. Basin-mean total rainfall from Japan Meteorological Agency’s analyzed radar rainfall (RADJ), Water and Disaster Management Bureau’s radar rainfall (RADW), Automated Meteorological Data Acquisition System (AMeDAS), and satellite-based rainfall data (GSMaP) were about 314, 322, 357 and 304 mm during July 5–7 2018. In this study, we applied Rainfall–Runoff–Inundation (RRI) to acquire a detailed understanding of flood processes in the Oda river basin. All the available rainfall data including different spatial resolution of hydrographic features were considered as the main input data in the model separately. Gridded flow and map of the possible maximum flood depth across the basins were generated and validated. Simulated results based on high resolution topographic data are more closely aligned with observed data. It is also found that the maximum flood inundation areas estimated by the RRI model using radar rainfall data appeared somewhat closer with the extent of flood-affected areas from the model with data of the Japanese Geospatial Information Authority (GSI) over the Mabi city. It is believed that modelled results can be used an important reference in the disaster mitigation and that they may be useful for further studies

AsiaPEX:Challenges and Prospects in Asian Precipitation Research

The Asian Precipitation Experiment (AsiaPEX) was initiated in 2019 to understand terrestrial precipitation over diverse hydroclimatological conditions for improved predictions, disaster reduction, and sustainable development across Asia under the framework of the Global Hydroclimatology Panel (GHP)/Global Energy and Water Exchanges (GEWEX). AsiaPEX is the successor to GEWEX Asian Monsoon Experiment (GAME; 1995-2005) and Monsoon Asian Hydro-Atmosphere Scientific Research and Prediction Initiative (MAHASRI; 2006-16). While retaining the key objectives of the aforementioned projects, the scientific targets of AsiaPEX focus on land-atmosphere coupling and improvements to the predictability of the Asian hydroclimatological system. AsiaPEX was designed for both fine-scale hydroclimatological processes occurring at the land surface and the integrated Asian hydroclimatological system characterized by multiscale interactions. We adopt six approaches including observation, process studies, scale interactions, high-resolution hydrological modeling, field campaigns, and climate projection, which bridge gaps in research activities conducted in different regions. Collaboration with mesoscale and global modeling researchers is one of the core methods in AsiaPEX. We review these strategies based on the literature and our initial outcomes. These include the estimation and validation of highresolution satellite precipitation, investigations of extreme rainfall mechanisms, field campaigns over the Maritime Continent and Tibetan Plateau, areas of significant impact on the entire AsiaPEX region, process studies on diurnal- to interdecadal-scale interactions, and evaluation of the predictabilities of climate models for long-term variabilities. We will conduct integrated observational and modeling initiative, the Asian Monsoon Year (AMY)-II around 2025-28, whose strategies are the subregional observation platforms and integrated global analysis.</p

Inundation Analysis of the Oda River Basin in Japan during the Flood Event of 6–7 July 2018 Utilizing Local and Global Hydrographic Data

During the first week of July 2018, widespread flooding caused extensive damage across several river basins in western Japan. Among the affected basins were the Mabicho district of Kurashiki city in the lower part of the Oda river basin of the Okayama prefecture. An analysis of such a historical flood event can provide useful input for proper water resources management. Therefore, to improve our understanding of the flood inundation profile over the Oda river basin during the period of intense rainfall from 5&ndash;8 July 2018, the Rainfall-Runoff-Inundation (RRI) model was used, with radar rainfall data from the Japan Meteorological Agency (JMA) as the input. River geometries&mdash;width, depth, and embankments&mdash;of the Oda river were generated and applied in the simulation. Our results show that the Mabicho district flooding was due to a backwater effect and bursting embankments along the Oda River. The model setup was then redesigned, taking into account these factors. The simulated maximum flood-affected areas were then compared with data from the Japanese Geospatial Information Authority (GSI), which showed that the maximum flood inundation areas estimated by the RRI model and the GSI flood-affected area matched closely. River geometries were extracted from a high-resolution digital elevation model (DEM), combined with coarser resolution DEM data (global data), and then utilized to perform a hydrological simulation of the Oda river basin under the scenarios of backwater effect and embankment failure. While this approach produced a successful outcome in this study, this is a case study for a single river basin in Japan. However, the fact that these results yielded valid information on the extent of flood inundation over the flood-affected area suggests that such an approach could be applicable to any river basin