Persistent mental health burden following climate-change–related extreme rainfall: Repeated cross-sectional population surveys in a flood-naïve region of Japan

Climate change is increasing the frequency of extreme rainfall events worldwide, yet evidence on their population-level mental health impacts—particularly in regions with no prior flood experience—remains limited. In July 2023, heavy rainfall caused widespread flooding in Akita Prefecture, Japan, a region historically unaccustomed to large-scale inundation. We conducted four independent, repeated cross-sectional surveys at approximately 3, 6, 9, and 12 months after the event to examine patterns of psychological distress and their association with disaster-related damage. Adult residents of Akita City completed validated Japanese versions of the Depression Anxiety Stress Scales (DASS-21), the Impact of Event Scale–Revised (IES-R; post-traumatic stress symptoms), and the Athens Insomnia Scale. Participants were classified according to whether they experienced any disruption to daily life, property, or housing due to the disaster. At the population level, median scores for depression, anxiety, stress, and post-traumatic stress symptoms were lower in later surveys than in the early post-disaster period. However, at every time point, individuals reporting any disaster-related damage exhibited substantially higher psychological symptom scores and a higher prevalence of screening-positive outcomes than those without damage. These between-group differences were largest in the early surveys and remained evident up to 12 months after the event. Patterns were consistent across multiple symptom domains, including depression, anxiety, stress, post-traumatic stress symptoms, and insomnia. These findings indicate that even moderate but unprecedented climate-related disasters can impose a sustained mental health burden at the population level, with disproportionately greater impact among affected residents. Our results underscore that psychological consequences may persist beyond physical recovery and reconstruction and highlight the importance of integrating long-term psychosocial support into climate change adaptation and disaster preparedness strategies, particularly in regions with limited prior exposure to flooding.