Spatial and temporal analysis of rainfall for obtaining mean areal rainfall on the event of heavy rain at Niigata prefecture in July 2004.

Abstract

Heavy rain was observed at Niigata, Fukushima and Fukui prefectures on 13th-19th Jul 2004. We had many flood damages accompaning this record-breaking rainfall. It was thought that the issue of this event was the horizontal heterogeneity of the rainfall because the heavy rainfall between 12th and 13th at Niigata was observed during long time at mountainous regions. We obtained maximum duration of record-breaking rainfall to use the gauge observation during 25 years and found that the duration near the region which had heavy rain was about 15-20 hours. Mean areal rainfall intensities at the catchment basin of Ikarashi river and Kariyata river were obtained with the Thiessen weighting scheme, the isohyet method and radar observations corrected by the gauge observations. It was found that the horizontal distribution in high resolution of the rainfall intensity was important to obtain the mean areal rainfall correctly in the case of this event.