Variability in Intensity of Heavy Rainfall Due to Climate Change and Its Impact on Paddy Inundation in Low‐lying Areas of Japan

The aim of this study was to detect changes in heavy rainfall patterns and to evaluate the impact of these changes on drainage systems in low‐lying areas. Our study area was in the Kaga three‐lagoon basin in Ishikawa Prefecture, Japan. First, heavy rainfall events were extracted from observed rainfall data from 1940 through 2008. Comparison of the hourly data showed that the average maximum 6‐, 12‐, 24‐, and 48‐h rainfall increased slightly over the 69 years and that the distribution of the maximum amount of 6‐h rainfall also changed. Next, rainfall data predicted by MIROC were examined. The results implied that the amount of rain in 3‐day rainfall events with a 10‐yr return period would reach a peak of 1.23 times the present amount in the near future. At the same time, a drainage analysis model was developed consisting of kinematic and diffusive tank models. The rainfall predicted by MIROC was used in the models to assess the impact of climate change on drainage systems. As a result, the duration of paddy inundation to a depth of more than 30 cm was estimated to increase in the future. Countermeasures, such as the improvement of pumping capacity, are suggested.