Rice cultivation system is directly affected by climate conditions and changes. This study aimed to analyze the impact of climate change on the water requirements of agricultural reservoirs using a reservoir water-balance model that includes climate change data, the paddy rice growing season and changes in land use. The results showed that due to increasing temperature, transplanting and heading dates were delayed 5-25 days and 0-10 days, respectively, in comparison to the baseline. The decrease in rates could be the result of IWR and increasing watershed runoff (average 10.7% to 27.0%). The results of this study can be used to estimate the capacity and capability of agricultural water resources. Our results also contribute to the establishment of countermeasures against possible risks and the development of policies for future agricultural water management.