Abstract
In order to categorize the solutions to the problems that occur when constructing the flood forecasting system for small and medium-sized rivers, we constructed the flood forecasting system for 125 rivers in Japan. During the construction, the following problems arose. (1) The reproducibility of the water level hydrograph in a small basin is low due to the influence of the analysis rainfall specifications. (2) The water budget does not match due to the accuracy of the rainfall product. (3) Low water reproducibility is low due to reduced the accuracy of HQ formula. As solutions to these problems, we proposed (1) use of a rainfall product with finer temporal resolution, (2) use of other rainfall products such as high-resolution precipitation nowcast, and (3) re-creation of the HQ formula by correcting the cross section. In particular, the accuracy of rainfall products is affected by the spatial position of rivers and the rainfall distribution during floods, so it is important from the viewpoint of model building to select an appropriate rainfall product by checking the water budget and comparing it with the ground rainfall.
