One-year meteorological radar observations (from November 2006 to October 2007) over a region from the west coast of central Sumatera (Sumatra) through the Mentawai Strait (about 130-km width) to Siberut Island were analyzed, and modulation of rainfall diurnal cycle (DC) in the region by the Madden−Julian oscillation (MJO) was studied. The DC peaked in the afternoon over Sumatera and Siberut islands, and in the nighttime/early morning over Mentawai Strait between the islands. Over the strait, offshore (westward) migration of the DC peak was distinct when the MJO active phase was propagating eastward over the Indian Ocean, whereas the migration was indistinct after the active phase passed over Sumatera. When the MJO active phase was propagating eastward over the eastern Indian Ocean, the DC was amplified, and daily rainfall maximum tended to appear over western Sumatera including the strait. The DC peak originating from Sumatera reached Siberut, and the DC over Siberut had an additional, stronger rainfall peak after midnight.

In this study, daily-observed data from 481 rain gauges were used to build a new gridded rainfall dataset for Vietnam based on the Spheremap interpolation technique. The new dataset, called Vietnam Gridded Precipitation (VnGP) Dataset has the resolution of 0.25° and covers the period 1980−2010. The validation was done for VnGP by assessing the spatial distribution, correlations, mean abosolute errors, root mean square errors with gauge observations. Results showed that VnGP had a relatively better performance compared to the datasets that used different interpolation techniques or used less number of input rain gauges. VnGP is currently available at the Data Integration and Analysis System (DIAS) managed by the

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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.

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 5–8 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—width, depth, and embankments—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.

<p>The near surface rain (NSR) dataset of the Tropical Rainfall Measurement Mission (TRMM) Precipitation Radar (PR) and the Global Precipitation Mission (GPM) Dual Precipitation Radar (DPR) was validated using around 40 tipping bucket raingauges installed over the northeastern Indian subcontinent, and disdrometers in the Meghalaya Plateau, India. The comparison during 2006-2014 showed significant overestimation of TRMM PR in Assam and Bengal plains during pre-monsoon season (March to May), and significant underestimation of TRMM PR over the Indian subcontinent during monsoon season (June to September). Whereas, the comparison during 2014-2019 showed significant overestimation of GPM DPR over only Meghalaya during monsoon season. The validation of rain-drop size distribution parameters: Dm and Nw showed positive correlation between GPM DPR derived values and Parsivel disdrometers observed ones, while unrealistic concentration of Nw on 30-40 dB was derived by GPM DPR. In the southern slope of the Meghala Plateau, NSR of TRMM PR at Cherrapunji, where is known as the heaviest rainfall station, on the plateau observed smaller rainfall than that in the adjacent valley. However, newly installed raingauges in the valley showed rather less rainfall than that on the plateau. The validity of the satellite derived rainfall distribution over the complicated terrain are discussed.</p>

<p>The Asian summer monsoon system is the strongest monsoon circulation on the Earth. A huge reversal of meridional temperature gradient develops over the area covering the hemispheric region due to strong diabatic heating associated with convective activities. Vigorous conventions reach the upper troposphere providing a great amount of high potential temperature airmass. This high potential temperature air mass originates from the high equivalent potential temperature airmass accumulated in the lower troposphere over the Asian monsoon region. The highest potential temperature tropospheric air mass is observed only over the Asian summer monsoon region. To get a total view of the Asian summer monsoon circulation system, we focused on the mass budget of the upper-tropospheric air mass with a potential temperature between 355K to 370K. The non-conservative change of the air mass corresponds with the diabatic heating due to the convective activities, and the diabatic cooling due to the radiative process. To analyze the radiative cooling process that takes place in the upper troposphere, we utilized hourly GSMaP pixel values to detect rain-free pixels of the ERA5 dataset. We calculated the non-conservative air mass tendency over the rain-free pixels on a daily and 0.5 degrees spatio-temporal scale. We found the radiative equilibrium amount of high potential temperature air mass and the Newtonian cooling process with a relaxation time scale of 6 to 7 days. We will show the quantitative estimates of the total convective process of the Asian summer monsoon system associated with the convective clouds and radiative processes, through the mass budget of 355K-370K potential temperature air mass. We will further show results of the evaluation of the accuracy of TRMM and GPM products using our high-resolution tipping bucket raingauge network distributed over the Northeastern Indian subcontinent.</p>

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, 2006-2016). 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 high-resolution 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 2025-2028, whose strategies are the sub-regional observation platforms and integrated global analysis.