Debris flows, landslides and landslips are recognized as severe disasters. The warning system is very important for protecting human lives from these disasters. In the current warning system, the warning is issued if the predicted total effective rainfall and effective precipitation intensity exceed certain criterion determined from past occurrences of such disasters. The historical maximum rainfall up to one or two hours is used as the predicted rainfall. In this system, unnecessary evacuations may tend to occur depending on the location or the predetermined criterion. The short term rainfall forecasting (nowcast) has not been used.
In contrast, introducing the nowcast to the warning system, we have developed a method to calculate the probability distribution of near future rainfall by radar. For example, it can be used for deriving upper confidence limit value of rainfall in arbitrary confidence level and the value will be substituted for the historical maximum rainfall in the warning system. We have estimated the effectiveness of the warning system using the method that predicts probability distribution of rainfall.