Abstract. Accurate estimation of the low-flow discharge is very important in evaluating the impact of climate change on water resources. This study focuses on the storage–discharge equation and the optimal parameters of the low flow. In order to investigate the sensitivity of the two parameters in the process of the calculation of low flow, we prepared 19 900 sets of the two parameters in the storage–discharge equation and carried out hydrological analysis using the hourly hydrological model presented by Fujimura et al. (2012). The study basins are the Sameura Dam basin (SAME basin) located in western Japan which has variability of rainfall, and the Shirakawa Dam basin (SIRA basin) located in a region of heavy snowfall in eastern Japan. The period of available hydrological data is 20 years for the SAME basin and 10 years for the SIRA basin. The results suggest that the optimal combination of two parameters can be identified by exponential equations. This study also estimates the annual water balance for the two basins based on hydrological analysis using the optimal parameters in the storage–discharge equation of low flow.