In the Tohoku District of Japan, river water is abundant from April to late July, but in August, it decreases. Consequently, water shortages occur once every several years. To mitigate the effects of such shortages, we developed a water-storage type deep-irrigation regime to store irrigation water in paddy fields. In conventional water management of Japan, water storage capacity is very low because irrigation is intermittent and the maximum water level in paddy fields is about 10 cm. On the other hand, in a water-storage type deep-irrigation regime, irrigation is not intermittent and the maximum water level is about 25 cm. Another objective of this irrigation method is protection of young panicles from low temperatures. In 2003, cold summer weather greatly lowered yields of rice throughout the Tohoku District. In 2003, we examined the effects of this irrigation regime on growth, yield and floral sterility caused by cold damage to rice cultivars. For each cultivar, the maximum number of tillers was less in the deep-irrigation plot than in the conventional irrigation plot. The ratio of the maximum tiller number in the deep-irrigation plot to that in the conventional-irrigation plot differed among cultivars. The percentage of ripening and yield were higher in the deep-irrigation plot than in the conventional-irrigation plot in almost all cultivars. In this experiment, cold weather damage was mitigated in a water-storage type deep-irrigation regime, but the extent of mitigation of cool summer damage differed among cultivars.