STATISTICAL ANALYSES OF THE TRANSITION OF FLOODING RISK ALONG THE NAKA AND KUJI RIVER, IBARAKI PREF

Abstract

The purpose of the research was to analyze statistically the long-term trend of the precipitations in the Naka river and the Kuji river basin in Ibaraki and Tochigi prefecture, by using the precipitations and the amount of river flow data for the decades. The data were offered by Hitachi river and road office of the Ministry of Land, Infrastructure and Transport. The second version of the climate scenario developed by the Japanese Meteorological Agency was also analyzed for the projections the precipitations in 2050 and 2100.Statistical analyses of the precipitation and the river flow data in the Naka and Kuji river basins revealed the clear increasing trend of the extreme precipitations (the yearly maximum of the daily precipitations) has been observed so far. On the contrary, the river flow data did not show such clear increasing trend as the precipitation. This may suggest the performance of the countermeasures to the river flood.The same statistical analyses applying to the climate scenario data did not indicate a clear increasing trend of the extreme precipitations in the future for 2050 and 2100.