Application of Easily- and Visually-recognizable Meteorological Radar Products for Early Detection of Heavy Rainfall Occurrence

　　In Japan, river and debris flow disasters have been frequently caused by heavy rainfall occurrence. Heavy rainfall and associated serious debris flow disasters occurred in 1999, and on August 20, 2014 in Hiroshima city located in the west of Japan. Many local residents were lost by the direct damage of debris flows. Currently, it is very difficult to predict numerically-based heavy rainfall and associated landslide accurately. This problem has led to the delay of evacuation of local residents. Therefore, the use of meteorological radar information is required for enhancing decision-making ability to urge the evacuation of local residents by local government staffs prior to the occurrence of the heavy rainfall disaster. It is also desirable that the local residents acquire the ability to determine the evacuation immediately after confirming radar information by themselves. However, it is difficult for untrained local residents and local government staffs to easily recognize where heavy rainfall occurs locally for a couple of hours because the image of radar echoes are equivalent to instant electromagnetic distribution measured per a couple of minutes, and the distribution of the radar echoes moves together with the movement of a synoptic system although meteorologically-sophisticated decision-maker may be able to recognize the possibility of heavy rainfall and associated disasters only by using instant radar information. In other words, easily- and visually-recognizable radar products which the untrained local residents and local government staffs are able to use are required for decision-making the evacuation from disastrous heavy rainfall. 　　Therefore, in this study, considering that the movement of radar echoes also may stop in a specific area if a synoptic system becomes stationary, radar-based accumulated rainfall information is defined here. The rainfall product is derived by the integration of radar intensity measured every ten minutes during previous 1 hours. Using this product, it was investigated whether and how the radar-based hourly rainfall displayed at an interval of ten minutes can be applied for early detection of heavy rainfall occurrence. From the results, it was found that 1) behaviors of heavy rainfall concentrating in a specific area can be easily and visually recognized in comparison with conventional radar information, and 2) real-time radar-based hourly rainfall displayed an interval of ten minutes effectively contributes to early detection of heavy rainfall occurrence. Therefore, it is desirable that such an accumulated radar product is applied for early recognition of heavy rainfall and associated debris flow disasters for municipal disaster-proof staffs and local residents. Moreover, it is expected that the radar product becomes one of important sources for early evacuation of local residents living along a mountain slope.