The torrential rain (named “the July 2018 heavy rain”) from June 28 to July 8 in 2018 resulted in tremendous human and property damage. There were 237 deaths and 7,173 cases of flooding above the floor level. During the torrential rain, the low rate of evacuation behavior of residents in the affected area was also a problem. The Okayama prefecture conducted a mail survey with residents that suffered housing damage caused by the torrential rain (valid sample n = 3,765). The survey measured what residents’ awareness and knowledge were of flooding before the torrential rain, residents’ prediction of flooding and choice and reason of evacuation behavior during the emergency heavy rain warning and the evacuation order (emergency). This study analyzed the determinants of residents’ evacuation behaviors during the torrential rain with the survey data. The results indicated that, although most residents were aware of hazard maps before the torrential rain, few predicted flooding. Most residents were aware of the evacuation shelters and had a prior evacuation plan. However, some residents made no attempt to evacuate, even when their houses were damaged. During the emergency heavy rain warning, feeling a sense of crisis was an important factor to promote evacuation behavior. And, during the evacuation order (emergency), the majority of those who took actual evacuation behaviors was those who were approached by public sectors such as the fire department and the police. Moreover, residents’ judgment based on scientific information such as hazard maps and prediction of flooding before the torrential rain had little effect on evacuation behavior during the emergency heavy rain warning and the evacuation order (emergency). Therefore, the study indicates the importance of approaching residents’ affective decision-making, instead of relying on rational decision-making, to promote evacuation behavior when people are in unusual situations.

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