The field of Intelligent Transport Systems, including the autonomous cars, has drawn great attention to information of weather forecasting. For efficiently navigating a moving vehicle to a safer route, it is urgent to detect big drops in the sky earlier before forming a localized heavy rainfall. This study aims to propose a new method based on estimating the median of raindrop size distribution from the observation of X-band polarimetric radars. Then, this method utilizes to verify the lead time of big drops detected in the sky before reaching the ground. As a result, we have fitted data included large raindrops with a new curve for estimating the median of raindrop size distribution using differential reflectivity calculated by 2DVD data. In addition, according to case study of localized heavy rainfall events, big drops can be detected at the height of 500 m using the three-dimensional data of polarization parameters in XRAIN, which is more than 5 minutes earlier than rain gauges recorded the corresponding rainfall. This result has testified the possibility of early detection of a heavy rainfall by using the observation of XRAIN.

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 Railway operators enforce train operation control such as speed reduction and suspension of operations based on precipitation observed by rain gauges to ensure safe train operation in the times of heavy rainfall. Many railway operators install rain gauges at intervals of approximately ten kilometers. These rain gauges can generally detect heavy rainfall occurring along rail lines, but cases are also encountered in which localized heavy rainfall goes undetected. Therefore, we developed a train operation control method utilizing radar precipitation that can detect localized heavy rainfall undetected by rain gauges. In this study, we evaluated the new method from the aspects of both safety and stability of train operation using Radar/ Rain-gauge analyzed precipitation data, rain gauge data observed by East Japan Railway Company (JR East), and rainfall disaster data occurred on the JR East lines. We propose that the current train operation control method using rain gauges be continued, to be supplemented by Radar/ Rain-gauge analyzed precipitation.

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 Future changes of probability distributions of extreme rainfall and flood are analyzed using “Database for Policy Decision-Making for Future Climate Change, d4PDF” having 60-years climate simulations with 50 ensemble members for the historical experiment and 90 members for the future experiment. The magnitude of a largest-class flood equivalent to a 1000-years flood is also analyzed. The study basins are the Ara River basin (2940km²), the Shonai River basin (1010km²), and the Yodo River basin (8240km²) in Japan. The results show that 1) the frequency distributions of annual maximum 24-hours rainfall for d4PDF of the historical experiment match with the ones for observed data in the range of the non-exceedance probability less than 0.95; 2) the 200-years annual maximum 24-hours rainfall for the d4PDF of the future experiment is 1.3 to 1.4 times larger than the one of the historical experiment and 1.5 to 1.7 times larger for the annual maximum river discharge; 3) the 200-years annual maximum 24 hours rainfall for the d4PDF of the future experiment is equivalent to the one of 900 years of the historical experiment; and 4) the rainfall patterns that cause largest-class floods simulated by d4PDF well match with the one of large historic floods for the three basins.

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 Streamlines are significantly bent over and concentrated around diversion and intake works, which frequently brings spatial acceleration of fluid motion. A proper design of the diversion and intake structures is necessary in order to minimize flow acceleration and to prevent local scouring around the works. In this study, a three dimensional potential flow analysis was carried out in order to obtain a strict analytical solution of flow in which the water is laterally withdrawn and diverted from a straight channel with rectangular cross section. Since the momentum principle is absent in the present analysis, applicability of the solution is limited in a case when hydraulic gradient and eddy viscosity are negligibly smaller than the inertial force. Nevertheless, the potential flow analysis provides the first-order approximation for diversion and intake flows, which helps engineers for determining hydraulic conditions for detailed investigation by strict three dimensional dynamic models or laboratory experiments.

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