For quantitative precipitation estimation (QPE) using weather radar, the phenomenon known as the bright band (BB) appearing around the 0 °C level is recognized as an area of overestimation. Understanding the factors contributing to BB formation and its radar echo characteristics is crucially important to improve the accuracy of radar rainfall measurements by removing and correcting the BB region. We conducted observations of precipitation clouds during 2013–2019 using an X-band marine radar with high temporal and spatial resolution and a Micro Rain Radar in Sapporo, Hokkaido, Japan. During this period, we frequently observed phenomena such as multilayered BBs and oblique strong echo bands that slope diagonally from the upper to lower BBs.
　For this study, we conducted a case analysis of the oblique strong echo band which appeared on April 3, 2016. The oblique strong echo band is presumably to be composed of melting particles because both the downward Doppler vertical velocity and the differential reflectivity increased. Also, the cross-correlation coefficient decreased in the band. The oblique strong echo band was formed in the convergence zone of cold and moist air flowing from the southern region of the radar site towards the lower layer. Warm and dry air originates from the northern side and comprises melting particles transported by the lower-level jet within the cold air. Within the oblique strong echo band, the particles were vertically classified in the degree of melting while transported by a strong wind. Particles that had melted completely from upper BB were also observed simultaneously. The upper BB persisted for a long time during the approach of a warm front, where warmer air with positive temperatures was advected above the lower 0 °C level. Also, locale-scale meteorological conditions strongly influenced the formation of the lower BB and the oblique strong echo band.
　To improve the accuracy of QPE and to detect the vertical–horizontal multilayer structure of the rain–snow boundary, detailed case analyses of BB distributions must be accumulated using radar with high vertical resolution and using MP radars with hydrometeor classification capability.

　The Advanced Microwave Scanning Radiometer 2 (AMSR2) L2 soil moisture product in V3.0 from the Japan Aerospace Exploration Agency (JAXA) was evaluated using in situ hydrological data obtained during 2012-2021 on the Mongolian Plateau. Regarding the relation between the AMSR2 soil moisture from descending orbits and in situ measured soil moisture at 3 cm depth, the root mean square error (RMSE: m³/m³) and bias (m³/m³) values varied respectively from 0.025 to 0.063 and from 0.011 to -0.051. Comparison of the Soil Moisture and Ocean Salinity (SMOS) soil moisture product in V700 with AMSR2 L2 revealed that the AMSR2 observed surface soil moisture with nearly equal accuracy and stability to those of SMOS. However, the bias values of the AMSR2 soil moisture measurements were inferior to those of SMOS, which measured soil moisture at increased depths. The RMSE and bias values of AMSR2 were more dependent on rainfall conditions than those of SMOS. These results suggest that underestimation of AMSR2 soil moisture measurements possibly occurred because of the difference between the depth of AMSR2 observations and the in situ area averaged soil moisture measurements. Overall, the AMSR2 L2 soil moisture product, with its high measurement accuracy, has been useful for studying ground surface changes and for monitoring daily surface soil moisture over large grassland areas since 2012.

　Since 2021, Paddy Field Dam has been implemented in the Kuma River Watershed, where the recordable heavy rainfall caused severe floods in July 2020. Paddy Field Dam, which enhances the storage capacity of a paddy plot, begins to spread throughout Japan. However, there are few studies that evaluate the effect of Paddy Field Dam based on observation. In this study, we investigated Paddy Field Dam which was conducted in Yunomae-cho in Kuma Region and evaluated the peak-cut effect based on observation of rainfall. Field observation of hydrological items was conducted at two paddy plots; one plot was Paddy Field Dam and the other was not, in 2021 and 2022. Precipitation, flow volume of drainage water, and temporal changes of the depth at the plot were measured. In addition, drainage in rainfall events was simulated by a numerical model based on the water balance equation and the momentum equation. The peak of drainage from the paddy plot with the drainage control plate (the device of Paddy Field Dam) was reduced by 46 %-80 % compared to the paddy plot without the device in major rainfall events (maximum rainfall intensity from 15.5 to 30.0 mm h^-1) in 2022. However, it is suggested that the peak-cut effect of Paddy Field Dam depended on the water depth at the initial stage of rainfall event.

　This article has summarized the problems faced by small and medium-sized rivers in regions with rapid population decline and considered solutions. The length of rivers that must be managed by local governments is long, and it is difficult to immediately develop all small and medium-sized rivers. Additionally, there are significant constraints on the human resources available for river management. We showed several examples of river problems caused by these and population decline. Analysis on population change data showed that the length of rivers with no population in the Tohoku region is accelerating. There are many prefectures with many rivers with no population in the Tohoku, Chugoku-Shikoku, and Kyushu regions. Given these circumstances, we proposed “Kawa-jimai” (in Japanese), which involves renouncement of river management, and divided the timing and method into three categories, and discussed kawa-jimai for each category, focusing on costs. To promote kawa-jimai, the government should allocate areas that are managed or not managed for basins or rivers, develop human resources who can comprehensively design rivers suitable for the region, and improve flood control and water circulation to make use of limited human resources, and develop water experts who cover flood management, water resources, water environment, etc. In addition, it is necessary to develop policies with co-benefit in terms of both hardware and software, and to this end, collaboration across departments, industry, government, academia, and NGOs is desired.