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

Persistent mental health burden following climate-change–related extreme rainfall: Repeated cross-sectional population surveys in a flood-naïve region of Japan | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Persistent mental health burden following climate-change–related extreme rainfall: Repeated cross-sectional population surveys in a flood-naïve region of Japan Junko Okuyama, Shuji Seto, Toshiki Iwasaki, Hiroyuki Sasaki, Shinichi Egawa, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8495344/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 9 You are reading this latest preprint version Abstract 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. Health sciences/Health care Biological sciences/Psychology Social science/Psychology Health sciences/Risk factors climate change extreme rainfall mental health burden repeated cross-sectional study flood-naïve region Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction In recent decades, Japan has experienced a marked increase in the frequency and intensity of linear precipitation zones and extreme rainfall events, resulting in floods, landslides, and urban inundations (Yamada et al. 2020 ; Fujibe 2020 ; Coumou and Frieler 2015 ). These trends, widely attributed to anthropogenic warming and the atmosphere’s increasing moisture-holding capacity, have substantial implications for public health and community resilience. Globally, extensive research has examined the psychological and behavioral health impacts of large-scale climate-related disasters. Studies conducted after Hurricane Katrina in the US documented high prevalence of post-traumatic stress disorder (PTSD) and depression among displaced individuals (Kloos et al. 2009 ; Galea et al. 2007 ; LaJoie et al. 2010 ; Paxson et al. 2012 ; An et al. 2019 ). Similarly, investigations of the 2009 Black Saturday Wildfires in Australia revealed persistent grief and PTSD symptoms, with community resilience identified as a crucial protective factor (Wasiak et al. 2013 ; Bryant et al. 2014 ; Bryant et al. 2018 ). More recent work on Hurricane Sandy (Lowe et al. 2015 ; Lowe et al. 2016 ; Schwartz et al. 2017 ), the 2017–2018 Caribbean hurricane seasons (Schwartz et al. 2018 ; Grineski et al. 2020 ), Hurricane Ida (2021) (Wertis et al. 2023 ), and the 2022 Pakistan floods (Sawangchai et al. 2023 ) consistently demonstrated high levels of anxiety, depression, and trauma-related symptoms, particularly among displaced populations and those repeatedly exposed to extreme climate events. Beyond these catastrophic events, moderate-scale disasters have also been linked to adverse mental health outcomes, though they have received comparatively limited scholarly attention. For example, prolonged droughts in New South Wales, Australia, were associated with chronic stress and depressive symptoms among farmers (Sartore et al. 2008 ; Stain et al. 2011 ). Similarly, the 2016 floods in Simbach am Inn, Germany, were followed by heightened stress and sleep disturbances (Hieronimi et al. 2022 ), while the 2021 Texas winter storm caused anxiety and helplessness due to widespread power and water outages (Sugg et al. 2023 ). The 2023 Canadian wildfires likewise triggered anxiety associated with smoke exposure and evacuation experiences (Obuobi-Donkor et al. 2024 ). An emerging line of evidence has begun to explore small-scale yet locally significant weather events. For instance, the 2010 Brisbane floods in Australia caused short-term emotional distress, mitigated by strong community cohesion (Clemens et al. 2013 ). Contrastingly, despite causing fatalities—particularly among older adults—the 2010 heatwave that struck western Canada and the northwestern US has not yet been systematically examined for its psychological consequences. In Japan, the 2018 Western Japan heavy rainfall (Okayama floods), which resulted in over 200 fatalities, was associated with depressive and anxiety symptoms among evacuees; however, longitudinal psychological follow-up studies remain limited (Miyaji et al., 2022 ). To provide an overview of the global distribution of psychological research on weather-related disasters, Table 1 summarizes major events and associated studies, classified by the magnitude of their physical and social impacts. Figure 1 illustrates this geographic and thematic imbalance. While large-scale disasters in North America, Australia, and Europe have been the focus of extensive psychological research, moderate- and small-scale disasters—particularly those occurring in East Asia—remain underrepresented despite evidence of considerable community disruption. Collectively, prior studies indicate that natural disasters’ psychological impacts are not necessarily proportional to the physical scale of damage. Rather, novelty, unpredictability, and disruption to daily life may be crucial in shaping mental health outcomes. This imbalance highlights a persistent research gap in understanding how non-catastrophic yet psychologically consequential disasters affect communities with limited prior exposure to such events. The 2023 Akita heavy rainfall represents a case in point. Although moderate in physical terms, this event was unprecedented for the region. Akita Prefecture—characterized by heavy snowfall, limited sunlight, and elevated suicide rates—had minimal historical experience with large-scale flooding. We therefore aimed to examine the psychological effects of this novel extreme rainfall event. We hypothesized that, even in the absence of substantial physical destruction, exposure to a first-time, climate-related disaster would be associated with sustained psychological distress, particularly among individuals who experienced housing or livelihood disruptions. Methods Study design This study employed a repeated cross-sectional design to examine population-level patterns of mental health following the July 2023 heavy rainfall disaster in Akita Prefecture, Japan. Independent samples of adult residents were surveyed at approximately 3, 6, 9, and 12 months after the event. Because different participants were recruited at each time point, the analyses focus on changes in distributions and between-group differences across survey waves, rather than within-individual trajectories or clinical attenuation. This design allows assessment of sustained mental health burden and disparities at the population level in a region with no prior large-scale flood experience. Repeated cross-sectional web-based monitoring To assess temporal changes in mental health, a series of four independent surveys were conducted using the Freeasy platform (iBridge Inc., Tokyo, Japan) at 3, 6, 9, and 12 months post-disaster. Each survey targeted Akita City residents aged 20–79, using quota sampling based on the city’s 2020 census to ensure balanced sex and age distributions. Sample sizes ranged from 400–1,000 per wave (total N ≈ 1,850). Participants provided electronic consent, and all surveys were approved by the Ethics Committee of the International Research Institute of Disaster Science, Tohoku University (approval numbers: 2020-003, 007, 040; 2021-020, 031; 2022-014). Community-based survey conducted with Akita Sakigake Shimpo To complement the web data, a postal and online survey was conducted jointly with Akita Sakigake Shimpo in June 2024, approximately 1 year post-disaster. Questionnaires were distributed to ~ 2,000 households in flood-affected districts of Akita City, with 640 valid responses obtained (response rate: 32%). This survey included DASS-21, IES-R, and additional items regarding housing damage, municipal support, and daily-life attenuation. Figure 2 illustrates the spatial extent of flooding, the distribution of survey participants across municipalities, and their demographic composition. The heaviest damage was concentrated in central Akita City, where 7,033 buildings were affected, including 11 total and 2,431 partial destructions. Response rates from these flood-affected districts were the highest seen, and participant demographics remained balanced across age groups throughout the four survey waves. Measures and analysis Psychological outcomes were assessed using validated Japanese versions of the DASS-21 (depression, anxiety, stress) and the IES-R (PTSD symptoms). For descriptive purposes, we reported subscale scores and the proportions exceeding established screening cut-offs. The IES-R was introduced starting from the 6-month survey and was therefore not administered at 3 months post-disaster. The primary exposure was disaster impact on housing and livelihood. Respondents were classified into five categories based on self-report: (1) no damage, (2) impact on work/daily life, (3) inundation of non-residential areas, (4) property damage, and (5) house damage. For the primary analysis, categories (2)–(5) were combined as “any housing/livelihood damage,” contrasted with “no damage.” A secondary, dose–response analysis treated the five categories as an ordinal gradient of impact severity. Because the four survey waves were independent (repeated cross-sectional design), time was modeled as a categorical factor (≈ 3, 6, 9, 12 months). Group differences in continuous outcomes were tested using Mann–Whitney U (two groups) or Kruskal–Wallis (≥ 3 groups), with post-hoc Dunn tests as appropriate. We report effect sizes (Cliff’s delta for two-group contrasts and epsilon-squared for Kruskal–Wallis) with 95% CIs. For binary outcomes (above vs. below screening cut-offs), prevalence ratios were estimated using robust Poisson regression with a log link, adjusting for age group (20–39, 40–64, 65–79 years) and sex; results are presented as adjusted prevalence ratios (aPRs) with 95% CIs. To evaluate whether attenuation differed by exposure, we compared temporal trends within exposure strata and tested exposure-by-time interactions in the robust Poisson models. P-values were two-sided with a significance threshold of 0.05; where multiple pairwise tests were conducted, Benjamini–Hochberg false discovery rate control was applied. Analyses were conducted in IPM SPSS Statistics (version 26). Ethical considerations The study adhered to the Declaration of Helsinki. Electronic or written informed consent was obtained. The protocol was approved by the Ethics Committee of the International Research Institute of Disaster Science, Tohoku University (approval numbers: 2020-003, 007, 040; 2021-020, 031; 2022-014). Data were anonymized and stored on secure institutional servers. Results Patterns of psychological distress across repeated cross-sectional surveys after the heavy rain Figure 3 illustrates patterns of psychological indicators across repeated cross-sectional surveys. DASS-21 and AIS scores are shown for 3, 6, 9, and 12 months after the disaster, whereas IES-R scores are presented for the 6-, 9-, and 12-month surveys, based on data from the Freeasy online panel restricted to Akita Prefecture. Overall, the median DASS-21 and IES-R scores declined gradually, although depressive and insomnia symptoms persisted longer than in other domains. Across the four survey waves (approximately 3, 6, 9, and 12 months post-disaster), population-level indices of psychological distress exhibited modest attenuation across survey waves (Table 2). Median DASS-21 Depression, Anxiety, and Stress scores declined significantly over time (Kruskal–Wallis tests, p = 0.017, 0.037, and 0.005, respectively), and IES-R PTSD scores exhibited a similar downward trend (p = 0.050). The median depression score decreased from 9 [2–18] at 3 months to 4 [0–16] at 12 months, anxiety from 14 [2–26] to 8 [0–22], stress from 8 [2–18] to 4 [0–16], and PTSD from 8 [2–24] to 3 [0–18]. These findings indicate that, at the prefectural level, psychological symptoms associated with the heavy rain event showed modest population-level attenuation over one year. Effect sizes for the overall temporal decline were small to moderate (ε² ≈ 0.03–0.05), suggesting a steady but modest attenuation across the population. Differential attenuation by damage to daily life, property, or housing When stratified by exposure, attenuation was largely confined to residents without any disaster-related damage to daily life, property, or housing (Table 3). In the no-damage group, median DASS-21 and IES-R scores declined steadily over time (pairwise post-hoc tests, FDR-adjusted p < 0.05), with small-to-moderate effect sizes. Contrastingly, participants reporting any damage showed persistently elevated scores through 12 months, with no statistically significant within-group decline on several indices after FDR correction. At approximately 3 months, the damaged group exhibited significantly higher symptom scores across all psychological domains compared with the undamaged group: DASS-21 Depression (p = 0.006, Cliff’s δ = 0.40), Anxiety (p = 0.002, δ = 0.30), Stress (p = 0.001, δ = 0.30), IES-R PTSD (p = 0.008, δ = 0.49), and AIS Insomnia (p = 0.002, δ = 0.51). Although group differences narrowed over time, between-group gaps remained detectable on several indices at 6 months (e.g., Anxiety p = 0.12, δ = 0.12; Stress p = 0.11, δ = 0.11; IES-R p = 0.10, δ = 0.10; AIS p = 0.070, δ = 0.24), indicating a slower attenuation pattern across survey waves among those experiencing any disruption to work or daily life, inundation of residential areas, damage to personal property (e.g., vehicles), or home flooding. Consistently, the prevalence of screening-positive outcomes (DASS-21 subscales and IES-R) remained higher in the damage group at each wave. Robust Poisson models adjusted for age and sex yielded elevated risks associated with any damage (aPRs > 1 across outcomes; 95% CIs not overlapping 1 for key endpoints at multiple time points). Exposure-by-time interaction terms indicated attenuation differed by exposure status, with weaker population-level attenuation among damage-exposed participants among the damage-exposed compared with the no-damage group (global interaction p < 0.05), supporting the interpretation that the absence of fatalities does not preclude prolonged psychological burden when daily life or property is affected. As illustrated in Fig. 5 , a detailed analysis of the IES-R subscale scores indicates that the disparity between the disaster-affected group and the non-affected group not only persisted but increased over the 12-month observation period. Specifically, the disaster-affected group consistently exhibited significantly higher levels of intrusion, avoidance, and hyperarousal symptoms compared to the non-affected group. In contrast, the non-affected group demonstrated a gradual decline in symptom severity across all subdomains. This growing divergence suggests that trauma-related symptoms—particularly hyperarousal and intrusive re-experiencing—either persisted or intensified among individuals directly impacted by disruptions to housing and livelihood. These findings imply a delay in psychological attenuation, despite visible progress in the physical reconstruction of the environment. Dose-response by severity category A secondary analysis treating the five exposure categories as an ordinal variable suggested a monotonic pattern: median symptom levels and screening-positive prevalence increased from no damage toward house damage, with significant trend tests (Jonckheere–Terpstra/Cuzick test, p < 0.05). While confidence intervals widened in the most severe category, the overall gradient supported a severity-dependent effect on psychological outcomes. Exploratory subgroup analyses Exploratory models adjusting for age and sex showed that the damage effect remained robust. Patterns were broadly similar across sex and age strata; where deviations appeared (e.g., relatively slower decline among older adults or women on selected subscales), interaction terms did not consistently reach significance after FDR correction. Figure 4 shows the correlations between age and psychological indicators across all survey waves. At 3 months, Spearman’s ρ ranged from − 0.16 to − 0.18 for DASS-21 subscales and − 0.17 for insomnia (all p ≤ 0.001). Similar inverse associations persisted at 6 months (ρ = −0.11 to − 0.16, p ≤ 0.002), weakened by 9 months (ρ ≈ −0.06 to − 0.02, p > 0.05), and re-emerged modestly at 12 months (ρ = −0.12 to − 0.16, p < 0.001). These patterns indicate that older participants consistently reported lower psychological distress, a finding distinct from prior disaster studies where aging was typically associated with poorer mental health (see Discussion; Supplementary Table S1 ). Given limited power for multiway stratification in a repeated cross-sectional design, these findings are interpreted cautiously. Discussion This study integrated repeated cross-sectional web-based monitoring and a community-based survey to elucidate the long-term psychological consequences of the July 2023 Akita heavy rainfall—a disaster that caused minimal physical destruction but was unprecedented in regional experience. Across the four post-disaster surveys, overall psychological indicators—depression, anxiety, stress, PTSD symptoms, and insomnia—showed modest population-level attenuation across survey waves. However, when stratified by exposure, attenuation trajectories diverged sharply: residents who experienced any damage to daily life, property, or housing remained at higher levels of psychological distress throughout the year. By 12 months, the gap between the damaged and undamaged groups had become even more pronounced across all scales (DASS-21, IES-R, AIS), revealing that psychological symptom attenuation lagged behind physical recovery and reconstruction. These results demonstrate that moderate but novel disasters can generate enduring mental-health disparities, underscoring the necessity for sustained psychological support beyond the acute attenuation phase. Subscale analyses (Fig. 5 ) further elucidated that the observed disparities were particularly pronounced in the intrusion and hyperarousal dimensions of the IES-R, both of which index persistent re-experiencing and heightened physiological arousal. In contrast, the avoidance subscale demonstrated a relatively attenuated decline among residents whose homes had not sustained direct damage, indicating that individuals experiencing direct structural damage continued to exhibit sustained hypervigilance and recurrent cognitive and emotional reminders of the disaster. These findings suggest a widening psychological gap over time between residents differentially affected by the event, aligning with a pattern of diverging population-level attenuation across survey waves that has been reported after moderately severe yet moderate in physical magnitude yet unprecedented in local experience. Such divergence may be exacerbated by secondary stressors—such as delayed compensation, prolonged reconstruction efforts, and perceived disparities in attenuation processes—which may serve to perpetuate trauma-related symptoms even after physical safety has ostensibly been reestablished. Comparison with previous studies Consistent with the temporal trends shown in Table 2, psychological symptoms among residents of Akita Prefecture gradually decreased over the 12 months following the disaster, indicating partial attenuation at the population level. The present findings align with international research showing that floods and storms, even of moderate magnitude, can lead to long-term psychological distress (Goldmann and Galea 2014 ; Tang et al. 2014 ). Reported PTSD prevalence after floods typically ranges from 10–30%, comparable to the elevated distress observed here. In Japan, studies following the Great East Japan Earthquake revealed persistent psychological symptoms years later (Orui et al. 2014 ), emphasizing the chronic nature of disaster-related mental health challenges. Unlike those large-scale disasters, however, the Akita event was characterized by limited physical damage but high novelty value. Residents had little prior experience with severe rainfall or flooding, which likely heightened perceived threat and uncertainty. This aligns with cognitive and behavioral frameworks, suggesting that unexpected or uncontrollable events evoke stronger stress responses, even when objective losses are modest. Distinctive features of “moderate but unprecedented” disasters Conventional disaster-psychology models posit that there exists a proportional relationship between physical damage and psychological impact. The present results challenge this assumption. The Akita rainfall, though moderate in scale, produced long-lasting psychological effects comparable to those observed after large disasters. Residents accustomed to heavy snowfall and limited sunlight faced a qualitatively new hazard—flooding—which disrupted their sense of environmental safety and community continuity. Prolonged inconveniences, such as delays in home repair, disruption to workplaces and transport, and social comparison with less-affected peers, likely reinforced stress over time. The re-expansion of between-group disparities at 12 months suggests that differential access to attenuation resources and coping capacity led to a widening of psychological inequality even as visible reconstruction progressed. Age and psychological resilience after the Akita rainfall The observed inverse association between age and psychological distress adds an important nuance to the understanding of post-disaster adaptation. Previous flood-related research has typically reported poorer mental health outcomes among older adults, often attributing these findings to greater physical vulnerability, pre-existing medical conditions, and mobility limitations that hinder evacuation or access to resources (Iqbal et al., 2023 ; Mulchandani et al., 2019 ). In contrast, our data show that older participants in Akita exhibited lower levels of depression, anxiety, stress, and insomnia across most post-disaster periods. This reversal may reflect the moderate scale of the event and the absence of mass evacuation requirements. Unlike catastrophic floods that disrupt living arrangements and social networks, the Akita rainfall allowed residents—particularly older adults—to remain within their familiar homes and communities, thereby preserving social continuity and perceived control. Additionally, the life-course perspective suggests that older individuals may possess stronger coping repertoires, accumulated through prior experiences with hardship or loss, which can buffer against stress in novel but non-life-threatening situations. Together, these findings imply that the psychological impact of a disaster depends not only on its physical severity but also on the degree to which it forces behavioral displacement and challenges established routines. Implications for disaster mental health and policy These findings highlight the need for both early and long-term psychosocial intervention following disasters, regardless of their physical magnitude. As shown in Table 2, psychological symptoms among the overall population gradually declined across the first post-disaster year, suggesting a certain degree of natural attenuation. However, Table 3 demonstrates that individuals who experienced any disruption to daily life, property, or housing continued to show elevated distress levels up to 12 months, indicating a persistent psychological impact among directly affected residents. Disaster-response systems that allocate mental-health resources based solely on visible damage or casualty counts risk overlooking communities that experience enduring distress from disruption and uncertainty. Our 12-month data clearly show that psychological attenuation trails physical reconstruction. Therefore, municipalities should maintain accessible counseling, outreach, and peer-support programs for at least one to two years after an event. The collaboration with Akita Sakigake Shimpo demonstrates the practical value of community-based participatory approaches in identifying at-risk groups and sustaining engagement through local media. At a national level, the rising frequency of linear precipitation zones and extreme rainfall events in Japan (Yamada et al. 2020 ; Kawaguchi et al. 2023) demands that mental-health perspectives be integrated into climate-adaptation policies. Preparedness plans should explicitly include mechanisms for prolonged psychological monitoring and multi-year support for residents in newly affected regions. Limitations and future directions Several limitations warrant consideration. First, web-based recruitment may have underrepresented residents without internet access or those experiencing severe hardship. Second, while the community survey provided valuable cross-validation, longitudinal follow-up of the same participants would better delineate causal pathways. Third, psychological data were derived from validated self-report scales rather than clinical interviews. Future work should combine repeated community assessments with objective indicators—such as sleep, activity, or biological stress markers—to clarify how “first-time disaster experiences” translate into chronic psychological sequelae. Conclusion Although the 2023 Akita heavy rainfall caused only modest physical damage, it produced persistent and widening psychological disparities between affected and unaffected residents throughout the following year. The integration of repeated cross-sectional and community-based evidence underscores that even small-scale, moderate in physical magnitude yet unprecedented in local experience can impose lasting mental burdens that outlive physical recovery and reconstruction. Effective disaster attenuation must therefore encompass not only infrastructure reconstruction but also long-term psychosocial support to restore community well-being. Even when physical scars fade, psychological wounds may remain—particularly in regions unaccustomed to such climate-related disruptions. Declarations Contributions Conception or design of the work: J.O., S.S., M.M.; Data cleaning: H.S., S.E.; Data analysis and interpretation: T.I., S.F.; Drafting the article: J.O., S.S.: Critical revision of the article: T.I., S.F.; Final approval of the version to be published: J.O., S.S., F.I., K.H. All authors read and approved the final manuscript. Competing interests The authors declare no competing interests Funding This research was supported by the Innovative Research Program on Suicide Countermeasures [Grant Number: JPSCIRS20220301], KAKEN Grant-in-Aid for Early-Career Scientists [Grant Number: 22K15780], and the International Research Institute of Disaster Science, Tohoku University. Author Contribution Conception or design of the work: J.O., S.S., M.M.; Data cleaning: H.S., S.E.; Data analysis and interpretation: T.I., S.F.; Drafting the article: J.O., S.S.: Critical revision of the article: T.I., S.F.; Final approval of the version to be published: J.O., S.S., F.I., K.H. 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Wasiak, J. et al. 12-month generic health status and psychological distress outcomes following an Australian natural disaster experience: 2009 Black Saturday Wildfires. Injury 44 (11), 1443–1447 (2013). Wertis, L., Runkle, J. D., Sugg, M. M. & Singh, D. Examining Hurricane Ida's impact on mental health: results from a quasi-experimental analysis. Geohealth. , 7(2), e2022GH000707. (2023). Yamada, T., Sato, T. & Nakamura, K. Characteristics of linear precipitation systems causing heavy rainfall in Japan. Atmosphere 11 , 1347 (2020). Tables Table 1 to 3 are available in the Supplementary Files section. Additional Declarations No competing interests reported. Supplementary Files Table120260101.xls Classification of Weather-Related Disasters by Magnitude, Year, Geographic Location, Psychological Studies, and Key Findings Disasters are categorized based on the magnitude of physical and social impact, including reported fatalities, infrastructure damage, and emergency response level. Within each category, events are listed chronologically. The number and scope of psychological studies vary substantially across events. Notably, small- and medium-scale disasters such as the 2018 Okayama floods and the 2023 Akita rainfall have received limited scholarly attention despite evidence of community-level psychological burden. Table220260101.xls Differences in Psychological (DASS-21 Depression/Anxiety/Stress; IES-R) and Sleep (AIS) Scores Between Participants With and Without Any Disaster-Related Damage Across Post-Disaster Time Points This table presents between-group comparisons by disaster-related damage status at each survey wave. Values are presented as median [IQR]. Group comparisons were conducted using the Mann–Whitney U test; Cliff’s δ indicates effect size. Participants were classified into five categories based on self-reported impact: (1) no damage, (2) disruption to work or daily life, (3) inundation of residential district, (4) damage to personal property (e.g., vehicles), and (5) flooding of residence. Categories (2)–(5) were combined as “any damage.” AIS = Athens Insomnia Scale; IES-R = Impact of Event Scale–Revised. Table320260101.xls Differences in psychological outcomes between participants with and without disaster-related damage This table summarizes between-group differences by disaster-related damage status, irrespective of survey wave. Values are presented as median [IQR]. Comparisons were conducted using the Mann–Whitney U test; Cliff’s δ indicates effect size. AIS = Athens Insomnia Scale; IES-R = Impact of Event Scale–Revised. SupplementaryTableS1CorrelationsAkita.xlsx Supplementary Table S1. Spearman’s rank correlations (ρ) between age and psychological indicators at 3, 6, 9, and 12 months after the 2023 Akita heavy rainfall. Cite Share Download PDF Status: Under Review Version 1 posted Reviews received at journal 01 May, 2026 Reviewers agreed at journal 21 Apr, 2026 Reviews received at journal 13 Apr, 2026 Reviewers agreed at journal 13 Mar, 2026 Reviewers agreed at journal 10 Mar, 2026 Reviewers invited by journal 16 Jan, 2026 Editor assigned by journal 02 Jan, 2026 Submission checks completed at journal 02 Jan, 2026 First submitted to journal 01 Jan, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8495344","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":577019127,"identity":"2f09dc59-5eca-4688-a62f-7c92bb90ee09","order_by":0,"name":"Junko 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04:35:56","extension":"xml","order_by":22,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":91880,"visible":true,"origin":"","legend":"","description":"","filename":"d30af4a195a548519abf9cad97dd77b21structuring.xml","url":"https://assets-eu.researchsquare.com/files/rs-8495344/v1/84b607a1477de7408c0bc6f5.xml"},{"id":100750733,"identity":"f89f0b10-b902-4dc1-af2c-efe6ff5b58a0","added_by":"auto","created_at":"2026-01-21 04:35:56","extension":"html","order_by":23,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":104412,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-8495344/v1/b03e9885dc8d1743bfb3202e.html"},{"id":100750720,"identity":"941c964a-7a20-448a-ac88-f2d2b79bbcd5","added_by":"auto","created_at":"2026-01-21 04:35:56","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":135816,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eGlobal Distribution of Psychological Studies on Weather-Related Disasters by Magnitude of Impact\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis figure presents major weather-related disasters that have been the subject of psychological research, categorized according to the severity of physical and social damage. Disasters are arranged chronologically within each impact category.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCircle colors indicate impact severity\u003c/strong\u003e:\u003c/p\u003e\n\u003cp\u003e● Red: High-impact disasters (extensive damage, high mortality, and widespread infrastructure loss)\u003c/p\u003e\n\u003cp\u003e● Light blue: Moderate-impact disasters (considerable but non-catastrophic damage)\u003c/p\u003e\n\u003cp\u003e● Yellow: Low-impact disasters (relatively limited damage, with few fatalities and minor structural losses)\u003c/p\u003e\n\u003cp\u003eWhile high-impact events have attracted substantial research attention, smaller-scale or regionally moderate in physical magnitude yet unprecedented in local experience—particularly in East Asia—have received comparatively little attention. This disparity underscores the need for broader investigations into the psychological impacts of moderate-intensity yet disruptive climate events.\u003c/p\u003e","description":"","filename":"OnlineFigure120260101.png","url":"https://assets-eu.researchsquare.com/files/rs-8495344/v1/d8cc0ce267a9557e0d525c04.png"},{"id":100750712,"identity":"640ba263-ced6-4ddc-b407-f25cfc55cda9","added_by":"auto","created_at":"2026-01-21 04:35:55","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":378797,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eDamage and participant distribution following the 2023 Akita heavy rainfall.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e(A) Map of major flooded areas in Akita City showing human and structural losses.\u003c/p\u003e\n\u003cp\u003e(B) Percentage of responses by municipality across the four survey waves (3, 6, 9, and 12 months).\u003c/p\u003e\n\u003cp\u003e(C) Respondents’ demographics by age group and degree of damage experienced.\u003c/p\u003e\n\u003cp\u003eInformation on rainfall and damage was obtained from Akita Prefecture (2024) and the Japan Automobile Federation Tohoku Branch (2023).\u003c/p\u003e\n\u003cp\u003eData for panels (B) and (C) were derived from the Akita Sakigake Shimpo community survey. (A) Map of major flooded areas in Akita City showing human and structural losses.\u003c/p\u003e","description":"","filename":"OnlineFigure220260101.png","url":"https://assets-eu.researchsquare.com/files/rs-8495344/v1/cbb3f0ef69f4f36be627e5cd.png"},{"id":100750738,"identity":"72eb6025-c674-4925-897d-4cad83d15044","added_by":"auto","created_at":"2026-01-21 04:35:57","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":187363,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePatterns of psychological indicators across repeated cross-sectional surveys among Akita residents after the 2023 heavy rainfall.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eBox plots show DASS-21 subscales (Depression, Anxiety, and Stress), AIS Insomnia, and IES-R PTSD scores at 6, 9, and 12 months after the heavy rainfall event.\u003c/p\u003e\n\u003cp\u003eMedian, interquartile range, and extreme values are indicated.\u003c/p\u003e\n\u003cp\u003eScores were obtained from repeated cross-sectional surveys using the Freeasy online panel, limited to residents of Akita Prefecture (N=398–612 per wave).\u003c/p\u003e\n\u003cp\u003eWhile modest population-level attenuation was observed across most indicators, depression and insomnia remained relatively elevated through 12 months.\u003c/p\u003e\n\u003cp\u003eError bars represent interquartile ranges.\u003c/p\u003e","description":"","filename":"OnlineFigure320260101.png","url":"https://assets-eu.researchsquare.com/files/rs-8495344/v1/ce1db67ff11b47cef6432d94.png"},{"id":100750736,"identity":"420fa23e-6022-45b8-820d-631aec910123","added_by":"auto","created_at":"2026-01-21 04:35:57","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":180559,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSpearman correlations between age and psychological scale scores at 3, 6, 9, and 12 months after the heavy rain disaster in Akita.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eScatterplots show the relationships between participants’ age and scores on the Depression, Anxiety, and Stress subscales of the DASS-21, the Athens Insomnia Scale (AIS), and the Impact of Event Scale–Revised (IES-R) at each follow-up point. Each panel presents Spearman’s correlation coefficient (ρ) and its significance level (p). Negative correlations indicate that younger participants tended to report higher psychological distress across the observation periods, whereas these associations gradually weakened over time.\u003c/p\u003e","description":"","filename":"OnlineFigure420260101.png","url":"https://assets-eu.researchsquare.com/files/rs-8495344/v1/a57171fdfecf4b340c33cf1a.png"},{"id":100750730,"identity":"53796a60-15b9-4355-8a3f-a60d4696930a","added_by":"auto","created_at":"2026-01-21 04:35:56","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":322277,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eChanges across repeated cross-sectional surveys in post-traumatic stress symptoms by exposure to disaster-related damage after the 2023 Akita heavy rainfall\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eBox plots illustrate subscale scores of the Impact of Event Scale–Revised (IES-R)—Intrusion, Avoidance, and Hyperarousal—at 6, 9, and 12 months after the heavy rainfall event, stratified by exposure to any disaster-related damage (left: Damaged Group; right: Non-Damaged Group).\u003c/p\u003e\n\u003cp\u003eEach box shows the median, interquartile range, and extreme values. The dashed horizontal line indicates the conventional screening cut-off for probable post-traumatic stress disorder.\u003c/p\u003e\n\u003cp\u003eParticipants reporting any disruption to work or daily life, inundation of residential districts, property loss, or housing damage were classified as the Damaged Group; others were classified as Non-Damaged.\u003c/p\u003e\n\u003cp\u003eData were derived from repeated cross-sectional surveys using the Freeasy online panel, restricted to residents of Akita Prefecture (N = 398–612 per wave).\u003c/p\u003e\n\u003cp\u003ePersistent elevation of IES-R subscale scores among the Damaged Group through 12 months highlights persistent relative elevation of psychological symptoms in the Damaged Group relative to the Non-Damaged Group. Because different participants were surveyed at each wave, these results reflect population-level patterns across survey waves rather than within-individual change, recovery, or symptom trajectories.\u003c/p\u003e","description":"","filename":"OnlineFigure520260101.png","url":"https://assets-eu.researchsquare.com/files/rs-8495344/v1/93875ecad385b4ccea2f943b.png"},{"id":101298913,"identity":"d36f43a7-1469-45ec-b52d-9be25da570f3","added_by":"auto","created_at":"2026-01-28 09:37:49","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2989041,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8495344/v1/f40fe138-b6e2-4dea-973b-7074a2c0407e.pdf"},{"id":100796686,"identity":"c6146468-6ef8-4016-8af3-28459b1c1c28","added_by":"auto","created_at":"2026-01-21 13:45:10","extension":"xls","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":45568,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eClassification of Weather-Related Disasters by Magnitude, Year, Geographic Location, Psychological Studies, and Key Findings\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eDisasters are categorized based on the magnitude of physical and social impact, including reported fatalities, infrastructure damage, and emergency response level. Within each category, events are listed chronologically.\u003c/p\u003e\n\u003cp\u003eThe number and scope of psychological studies vary substantially across events. Notably, small- and medium-scale disasters such as the 2018 Okayama floods and the 2023 Akita rainfall have received limited scholarly attention despite evidence of community-level psychological burden.\u003c/p\u003e","description":"","filename":"Table120260101.xls","url":"https://assets-eu.researchsquare.com/files/rs-8495344/v1/f8cd7ddb38920fcf6181d5c3.xls"},{"id":100750718,"identity":"f20ee6bb-9a41-4b86-a91a-96514de7e775","added_by":"auto","created_at":"2026-01-21 04:35:56","extension":"xls","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":41984,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eDifferences in Psychological (DASS-21 Depression/Anxiety/Stress; IES-R) and Sleep (AIS) Scores Between Participants With and Without Any Disaster-Related Damage Across Post-Disaster Time Points\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis table presents between-group comparisons by disaster-related damage status at each survey wave. Values are presented as median [IQR]. Group comparisons were conducted using the Mann–Whitney U test; Cliff’s δ indicates effect size.\u003c/p\u003e\n\u003cp\u003eParticipants were classified into five categories based on self-reported impact: (1) no damage, (2) disruption to work or daily life, (3) inundation of residential district, (4) damage to personal property (e.g., vehicles), and (5) flooding of residence. Categories (2)–(5) were combined as “any damage.”\u003c/p\u003e\n\u003cp\u003eAIS = Athens Insomnia Scale; IES-R = Impact of Event Scale–Revised.\u003c/p\u003e","description":"","filename":"Table220260101.xls","url":"https://assets-eu.researchsquare.com/files/rs-8495344/v1/3fd589a879c1cf7db34ec14f.xls"},{"id":100750722,"identity":"17dc7be0-9e50-4971-accf-ae1b74d89ef5","added_by":"auto","created_at":"2026-01-21 04:35:56","extension":"xls","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":45056,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eDifferences in psychological outcomes between participants with and without disaster-related damage\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis table summarizes between-group differences by disaster-related damage status, irrespective of survey wave. Values are presented as median [IQR]. Comparisons were conducted using the Mann–Whitney U test; Cliff’s δ indicates effect size.\u003c/p\u003e\n\u003cp\u003eAIS = Athens Insomnia Scale; IES-R = Impact of Event Scale–Revised.\u003c/p\u003e","description":"","filename":"Table320260101.xls","url":"https://assets-eu.researchsquare.com/files/rs-8495344/v1/066e35f534a565e7f71a57a5.xls"},{"id":100750732,"identity":"a5fe74b1-6305-4d80-9d4f-6bd78f3767d6","added_by":"auto","created_at":"2026-01-21 04:35:56","extension":"xlsx","order_by":4,"title":"","display":"","copyAsset":false,"role":"supplement","size":10729,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSupplementary Table S1. Spearman’s rank correlations (ρ) between age and psychological indicators at 3, 6, 9, and 12 months after the 2023 Akita heavy rainfall.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"SupplementaryTableS1CorrelationsAkita.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-8495344/v1/d44ba27c473d5a184b479246.xlsx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Persistent mental health burden following climate-change–related extreme rainfall: Repeated cross-sectional population surveys in a flood-naïve region of Japan","fulltext":[{"header":"Introduction","content":"\u003cp\u003eIn recent decades, Japan has experienced a marked increase in the frequency and intensity of linear precipitation zones and extreme rainfall events, resulting in floods, landslides, and urban inundations (Yamada et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Fujibe \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Coumou and Frieler \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). These trends, widely attributed to anthropogenic warming and the atmosphere\u0026rsquo;s increasing moisture-holding capacity, have substantial implications for public health and community resilience.\u003c/p\u003e \u003cp\u003eGlobally, extensive research has examined the psychological and behavioral health impacts of large-scale climate-related disasters. Studies conducted after Hurricane Katrina in the US documented high prevalence of post-traumatic stress disorder (PTSD) and depression among displaced individuals (Kloos et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Galea et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; LaJoie et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Paxson et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; An et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Similarly, investigations of the 2009 Black Saturday Wildfires in Australia revealed persistent grief and PTSD symptoms, with community resilience identified as a crucial protective factor (Wasiak et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Bryant et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Bryant et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). More recent work on Hurricane Sandy (Lowe et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Lowe et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Schwartz et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2017\u003c/span\u003e), the 2017\u0026ndash;2018 Caribbean hurricane seasons (Schwartz et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Grineski et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2020\u003c/span\u003e), Hurricane Ida (2021) (Wertis et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), and the 2022 Pakistan floods (Sawangchai et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) consistently demonstrated high levels of anxiety, depression, and trauma-related symptoms, particularly among displaced populations and those repeatedly exposed to extreme climate events.\u003c/p\u003e \u003cp\u003eBeyond these catastrophic events, moderate-scale disasters have also been linked to adverse mental health outcomes, though they have received comparatively limited scholarly attention. For example, prolonged droughts in New South Wales, Australia, were associated with chronic stress and depressive symptoms among farmers (Sartore et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Stain et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Similarly, the 2016 floods in Simbach am Inn, Germany, were followed by heightened stress and sleep disturbances (Hieronimi et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), while the 2021 Texas winter storm caused anxiety and helplessness due to widespread power and water outages (Sugg et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The 2023 Canadian wildfires likewise triggered anxiety associated with smoke exposure and evacuation experiences (Obuobi-Donkor et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eAn emerging line of evidence has begun to explore small-scale yet locally significant weather events. For instance, the 2010 Brisbane floods in Australia caused short-term emotional distress, mitigated by strong community cohesion (Clemens et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Contrastingly, despite causing fatalities\u0026mdash;particularly among older adults\u0026mdash;the 2010 heatwave that struck western Canada and the northwestern US has not yet been systematically examined for its psychological consequences. In Japan, the 2018 Western Japan heavy rainfall (Okayama floods), which resulted in over 200 fatalities, was associated with depressive and anxiety symptoms among evacuees; however, longitudinal psychological follow-up studies remain limited (Miyaji et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eTo provide an overview of the global distribution of psychological research on weather-related disasters, Table\u0026nbsp;1 summarizes major events and associated studies, classified by the magnitude of their physical and social impacts. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e illustrates this geographic and thematic imbalance. While large-scale disasters in North America, Australia, and Europe have been the focus of extensive psychological research, moderate- and small-scale disasters\u0026mdash;particularly those occurring in East Asia\u0026mdash;remain underrepresented despite evidence of considerable community disruption.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eCollectively, prior studies indicate that natural disasters\u0026rsquo; psychological impacts are not necessarily proportional to the physical scale of damage. Rather, novelty, unpredictability, and disruption to daily life may be crucial in shaping mental health outcomes. This imbalance highlights a persistent research gap in understanding how non-catastrophic yet psychologically consequential disasters affect communities with limited prior exposure to such events.\u003c/p\u003e \u003cp\u003eThe 2023 Akita heavy rainfall represents a case in point. Although moderate in physical terms, this event was unprecedented for the region. Akita Prefecture\u0026mdash;characterized by heavy snowfall, limited sunlight, and elevated suicide rates\u0026mdash;had minimal historical experience with large-scale flooding. We therefore aimed to examine the psychological effects of this novel extreme rainfall event. We hypothesized that, even in the absence of substantial physical destruction, exposure to a first-time, climate-related disaster would be associated with sustained psychological distress, particularly among individuals who experienced housing or livelihood disruptions.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStudy design\u003c/h2\u003e \u003cp\u003eThis study employed a repeated cross-sectional design to examine population-level patterns of mental health following the July 2023 heavy rainfall disaster in Akita Prefecture, Japan. Independent samples of adult residents were surveyed at approximately 3, 6, 9, and 12 months after the event. Because different participants were recruited at each time point, the analyses focus on changes in distributions and between-group differences across survey waves, rather than within-individual trajectories or clinical attenuation. This design allows assessment of sustained mental health burden and disparities at the population level in a region with no prior large-scale flood experience.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eRepeated cross-sectional web-based monitoring\u003c/h3\u003e\n\u003cp\u003eTo assess temporal changes in mental health, a series of four independent surveys were conducted using the Freeasy platform (iBridge Inc., Tokyo, Japan) at 3, 6, 9, and 12 months post-disaster. Each survey targeted Akita City residents aged 20\u0026ndash;79, using quota sampling based on the city\u0026rsquo;s 2020 census to ensure balanced sex and age distributions. Sample sizes ranged from 400\u0026ndash;1,000 per wave (total N\u0026thinsp;\u0026asymp;\u0026thinsp;1,850). Participants provided electronic consent, and all surveys were approved by the Ethics Committee of the International Research Institute of Disaster Science, Tohoku University (approval numbers: 2020-003, 007, 040; 2021-020, 031; 2022-014).\u003c/p\u003e\n\u003ch3\u003eCommunity-based survey conducted with Akita Sakigake Shimpo\u003c/h3\u003e\n\u003cp\u003eTo complement the web data, a postal and online survey was conducted jointly with Akita Sakigake Shimpo in June 2024, approximately 1 year post-disaster. Questionnaires were distributed to ~\u0026thinsp;2,000 households in flood-affected districts of Akita City, with 640 valid responses obtained (response rate: 32%). This survey included DASS-21, IES-R, and additional items regarding housing damage, municipal support, and daily-life attenuation.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e illustrates the spatial extent of flooding, the distribution of survey participants across municipalities, and their demographic composition. The heaviest damage was concentrated in central Akita City, where 7,033 buildings were affected, including 11 total and 2,431 partial destructions. Response rates from these flood-affected districts were the highest seen, and participant demographics remained balanced across age groups throughout the four survey waves.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eMeasures and analysis\u003c/h3\u003e\n\u003cp\u003ePsychological outcomes were assessed using validated Japanese versions of the DASS-21 (depression, anxiety, stress) and the IES-R (PTSD symptoms). For descriptive purposes, we reported subscale scores and the proportions exceeding established screening cut-offs. The IES-R was introduced starting from the 6-month survey and was therefore not administered at 3 months post-disaster.\u003c/p\u003e \u003cp\u003eThe primary exposure was disaster impact on housing and livelihood. Respondents were classified into five categories based on self-report: (1) no damage, (2) impact on work/daily life, (3) inundation of non-residential areas, (4) property damage, and (5) house damage. For the primary analysis, categories (2)\u0026ndash;(5) were combined as \u0026ldquo;any housing/livelihood damage,\u0026rdquo; contrasted with \u0026ldquo;no damage.\u0026rdquo; A secondary, dose\u0026ndash;response analysis treated the five categories as an ordinal gradient of impact severity.\u003c/p\u003e \u003cp\u003eBecause the four survey waves were independent (repeated cross-sectional design), time was modeled as a categorical factor (\u0026asymp;\u0026thinsp;3, 6, 9, 12 months). Group differences in continuous outcomes were tested using Mann\u0026ndash;Whitney U (two groups) or Kruskal\u0026ndash;Wallis (\u0026ge;\u0026thinsp;3 groups), with post-hoc Dunn tests as appropriate. We report effect sizes (Cliff\u0026rsquo;s delta for two-group contrasts and epsilon-squared for Kruskal\u0026ndash;Wallis) with 95% CIs. For binary outcomes (above vs. below screening cut-offs), prevalence ratios were estimated using robust Poisson regression with a log link, adjusting for age group (20\u0026ndash;39, 40\u0026ndash;64, 65\u0026ndash;79 years) and sex; results are presented as adjusted prevalence ratios (aPRs) with 95% CIs. To evaluate whether attenuation differed by exposure, we compared temporal trends within exposure strata and tested exposure-by-time interactions in the robust Poisson models. P-values were two-sided with a significance threshold of 0.05; where multiple pairwise tests were conducted, Benjamini\u0026ndash;Hochberg false discovery rate control was applied. Analyses were conducted in IPM SPSS Statistics (version 26).\u003c/p\u003e\n\u003ch3\u003eEthical considerations\u003c/h3\u003e\n\u003cp\u003e The study adhered to the Declaration of Helsinki. Electronic or written informed consent was obtained. The protocol was approved by the Ethics Committee of the International Research Institute of Disaster Science, Tohoku University (approval numbers: 2020-003, 007, 040; 2021-020, 031; 2022-014). Data were anonymized and stored on secure institutional servers.\u003c/p\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003ePatterns of psychological distress across repeated cross-sectional surveys after the heavy rain\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e illustrates patterns of psychological indicators across repeated cross-sectional surveys. DASS-21 and AIS scores are shown for 3, 6, 9, and 12 months after the disaster, whereas IES-R scores are presented for the 6-, 9-, and 12-month surveys, based on data from the Freeasy online panel restricted to Akita Prefecture. Overall, the median DASS-21 and IES-R scores declined gradually, although depressive and insomnia symptoms persisted longer than in other domains.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAcross the four survey waves (approximately 3, 6, 9, and 12 months post-disaster), population-level indices of psychological distress exhibited modest attenuation across survey waves (Table\u0026nbsp;2). Median DASS-21 Depression, Anxiety, and Stress scores declined significantly over time (Kruskal\u0026ndash;Wallis tests, p\u0026thinsp;=\u0026thinsp;0.017, 0.037, and 0.005, respectively), and IES-R PTSD scores exhibited a similar downward trend (p\u0026thinsp;=\u0026thinsp;0.050). The median depression score decreased from 9 [2\u0026ndash;18] at 3 months to 4 [0\u0026ndash;16] at 12 months, anxiety from 14 [2\u0026ndash;26] to 8 [0\u0026ndash;22], stress from 8 [2\u0026ndash;18] to 4 [0\u0026ndash;16], and PTSD from 8 [2\u0026ndash;24] to 3 [0\u0026ndash;18].\u003c/p\u003e \u003cp\u003eThese findings indicate that, at the prefectural level, psychological symptoms associated with the heavy rain event showed modest population-level attenuation over one year. Effect sizes for the overall temporal decline were small to moderate (ε\u0026sup2; \u0026asymp; 0.03\u0026ndash;0.05), suggesting a steady but modest attenuation across the population.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eDifferential attenuation by damage to daily life, property, or housing\u003c/h3\u003e\n\u003cp\u003eWhen stratified by exposure, attenuation was largely confined to residents without any disaster-related damage to daily life, property, or housing (Table\u0026nbsp;3). In the no-damage group, median DASS-21 and IES-R scores declined steadily over time (pairwise post-hoc tests, FDR-adjusted p\u0026thinsp;\u0026lt;\u0026thinsp;0.05), with small-to-moderate effect sizes.\u003c/p\u003e \u003cp\u003eContrastingly, participants reporting any damage showed persistently elevated scores through 12 months, with no statistically significant within-group decline on several indices after FDR correction. At approximately 3 months, the damaged group exhibited significantly higher symptom scores across all psychological domains compared with the undamaged group: DASS-21 Depression (p\u0026thinsp;=\u0026thinsp;0.006, Cliff\u0026rsquo;s δ\u0026thinsp;=\u0026thinsp;0.40), Anxiety (p\u0026thinsp;=\u0026thinsp;0.002, δ\u0026thinsp;=\u0026thinsp;0.30), Stress (p\u0026thinsp;=\u0026thinsp;0.001, δ\u0026thinsp;=\u0026thinsp;0.30), IES-R PTSD (p\u0026thinsp;=\u0026thinsp;0.008, δ\u0026thinsp;=\u0026thinsp;0.49), and AIS Insomnia (p\u0026thinsp;=\u0026thinsp;0.002, δ\u0026thinsp;=\u0026thinsp;0.51).\u003c/p\u003e \u003cp\u003eAlthough group differences narrowed over time, between-group gaps remained detectable on several indices at 6 months (e.g., Anxiety p\u0026thinsp;=\u0026thinsp;0.12, δ\u0026thinsp;=\u0026thinsp;0.12; Stress p\u0026thinsp;=\u0026thinsp;0.11, δ\u0026thinsp;=\u0026thinsp;0.11; IES-R p\u0026thinsp;=\u0026thinsp;0.10, δ\u0026thinsp;=\u0026thinsp;0.10; AIS p\u0026thinsp;=\u0026thinsp;0.070, δ\u0026thinsp;=\u0026thinsp;0.24), indicating a slower attenuation pattern across survey waves among those experiencing any disruption to work or daily life, inundation of residential areas, damage to personal property (e.g., vehicles), or home flooding.\u003c/p\u003e \u003cp\u003eConsistently, the prevalence of screening-positive outcomes (DASS-21 subscales and IES-R) remained higher in the damage group at each wave. Robust Poisson models adjusted for age and sex yielded elevated risks associated with any damage (aPRs\u0026thinsp;\u0026gt;\u0026thinsp;1 across outcomes; 95% CIs not overlapping 1 for key endpoints at multiple time points).\u003c/p\u003e \u003cp\u003eExposure-by-time interaction terms indicated attenuation differed by exposure status, with weaker population-level attenuation among damage-exposed participants among the damage-exposed compared with the no-damage group (global interaction p\u0026thinsp;\u0026lt;\u0026thinsp;0.05), supporting the interpretation that the absence of fatalities does not preclude prolonged psychological burden when daily life or property is affected.\u003c/p\u003e \u003cp\u003eAs illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e5\u003c/span\u003e, a detailed analysis of the IES-R subscale scores indicates that the disparity between the disaster-affected group and the non-affected group not only persisted but increased over the 12-month observation period. Specifically, the disaster-affected group consistently exhibited significantly higher levels of intrusion, avoidance, and hyperarousal symptoms compared to the non-affected group. In contrast, the non-affected group demonstrated a gradual decline in symptom severity across all subdomains. This growing divergence suggests that trauma-related symptoms\u0026mdash;particularly hyperarousal and intrusive re-experiencing\u0026mdash;either persisted or intensified among individuals directly impacted by disruptions to housing and livelihood. These findings imply a delay in psychological attenuation, despite visible progress in the physical reconstruction of the environment.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eDose-response by severity category\u003c/h2\u003e \u003cp\u003eA secondary analysis treating the five exposure categories as an ordinal variable suggested a monotonic pattern: median symptom levels and screening-positive prevalence increased from no damage toward house damage, with significant trend tests (Jonckheere\u0026ndash;Terpstra/Cuzick test, p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). While confidence intervals widened in the most severe category, the overall gradient supported a severity-dependent effect on psychological outcomes.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eExploratory subgroup analyses\u003c/h2\u003e \u003cp\u003eExploratory models adjusting for age and sex showed that the damage effect remained robust. Patterns were broadly similar across sex and age strata; where deviations appeared (e.g., relatively slower decline among older adults or women on selected subscales), interaction terms did not consistently reach significance after FDR correction. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e4\u003c/span\u003e shows the correlations between age and psychological indicators across all survey waves.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAt 3 months, Spearman\u0026rsquo;s ρ ranged from \u0026minus;\u0026thinsp;0.16 to \u0026minus;\u0026thinsp;0.18 for DASS-21 subscales and \u0026minus;\u0026thinsp;0.17 for insomnia (all p\u0026thinsp;\u0026le;\u0026thinsp;0.001).\u003c/p\u003e \u003cp\u003eSimilar inverse associations persisted at 6 months (ρ = \u0026minus;0.11 to \u0026minus;\u0026thinsp;0.16, p\u0026thinsp;\u0026le;\u0026thinsp;0.002), weakened by 9 months (ρ \u0026asymp; \u0026minus;0.06 to \u0026minus;\u0026thinsp;0.02, p\u0026thinsp;\u0026gt;\u0026thinsp;0.05), and re-emerged modestly at 12 months (ρ = \u0026minus;0.12 to \u0026minus;\u0026thinsp;0.16, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001).\u003c/p\u003e \u003cp\u003eThese patterns indicate that older participants consistently reported lower psychological distress, a finding distinct from prior disaster studies where aging was typically associated with poorer mental health (see Discussion; Supplementary Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). Given limited power for multiway stratification in a repeated cross-sectional design, these findings are interpreted cautiously.\u003c/p\u003e \u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eThis study integrated repeated cross-sectional web-based monitoring and a community-based survey to elucidate the long-term psychological consequences of the July 2023 Akita heavy rainfall\u0026mdash;a disaster that caused minimal physical destruction but was unprecedented in regional experience.\u003c/p\u003e \u003cp\u003eAcross the four post-disaster surveys, overall psychological indicators\u0026mdash;depression, anxiety, stress, PTSD symptoms, and insomnia\u0026mdash;showed modest population-level attenuation across survey waves. However, when stratified by exposure, attenuation trajectories diverged sharply: residents who experienced any damage to daily life, property, or housing remained at higher levels of psychological distress throughout the year.\u003c/p\u003e \u003cp\u003eBy 12 months, the gap between the damaged and undamaged groups had become even more pronounced across all scales (DASS-21, IES-R, AIS), revealing that psychological symptom attenuation lagged behind physical recovery and reconstruction. These results demonstrate that moderate but novel disasters can generate enduring mental-health disparities, underscoring the necessity for sustained psychological support beyond the acute attenuation phase.\u003c/p\u003e \u003cp\u003eSubscale analyses (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e5\u003c/span\u003e) further elucidated that the observed disparities were particularly pronounced in the intrusion and hyperarousal dimensions of the IES-R, both of which index persistent re-experiencing and heightened physiological arousal. In contrast, the avoidance subscale demonstrated a relatively attenuated decline among residents whose homes had not sustained direct damage, indicating that individuals experiencing direct structural damage continued to exhibit sustained hypervigilance and recurrent cognitive and emotional reminders of the disaster. These findings suggest a widening psychological gap over time between residents differentially affected by the event, aligning with a pattern of diverging population-level attenuation across survey waves that has been reported after moderately severe yet moderate in physical magnitude yet unprecedented in local experience. Such divergence may be exacerbated by secondary stressors\u0026mdash;such as delayed compensation, prolonged reconstruction efforts, and perceived disparities in attenuation processes\u0026mdash;which may serve to perpetuate trauma-related symptoms even after physical safety has ostensibly been reestablished.\u003c/p\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eComparison with previous studies\u003c/h2\u003e \u003cp\u003eConsistent with the temporal trends shown in Table\u0026nbsp;2, psychological symptoms among residents of Akita Prefecture gradually decreased over the 12 months following the disaster, indicating partial attenuation at the population level.\u003c/p\u003e \u003cp\u003eThe present findings align with international research showing that floods and storms, even of moderate magnitude, can lead to long-term psychological distress (Goldmann and Galea \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Tang et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Reported PTSD prevalence after floods typically ranges from 10\u0026ndash;30%, comparable to the elevated distress observed here. In Japan, studies following the Great East Japan Earthquake revealed persistent psychological symptoms years later (Orui et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2014\u003c/span\u003e), emphasizing the chronic nature of disaster-related mental health challenges.\u003c/p\u003e \u003cp\u003eUnlike those large-scale disasters, however, the Akita event was characterized by limited physical damage but high novelty value. Residents had little prior experience with severe rainfall or flooding, which likely heightened perceived threat and uncertainty. This aligns with cognitive and behavioral frameworks, suggesting that unexpected or uncontrollable events evoke stronger stress responses, even when objective losses are modest.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eDistinctive features of \u0026ldquo;moderate but unprecedented\u0026rdquo; disasters\u003c/h2\u003e \u003cp\u003eConventional disaster-psychology models posit that there exists a proportional relationship between physical damage and psychological impact. The present results challenge this assumption. The Akita rainfall, though moderate in scale, produced long-lasting psychological effects comparable to those observed after large disasters.\u003c/p\u003e \u003cp\u003eResidents accustomed to heavy snowfall and limited sunlight faced a qualitatively new hazard\u0026mdash;flooding\u0026mdash;which disrupted their sense of environmental safety and community continuity. Prolonged inconveniences, such as delays in home repair, disruption to workplaces and transport, and social comparison with less-affected peers, likely reinforced stress over time. The re-expansion of between-group disparities at 12 months suggests that differential access to attenuation resources and coping capacity led to a widening of psychological inequality even as visible reconstruction progressed.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003eAge and psychological resilience after the Akita rainfall\u003c/h2\u003e \u003cp\u003eThe observed inverse association between age and psychological distress adds an important nuance to the understanding of post-disaster adaptation.\u003c/p\u003e \u003cp\u003ePrevious flood-related research has typically reported poorer mental health outcomes among older adults, often attributing these findings to greater physical vulnerability, pre-existing medical conditions, and mobility limitations that hinder evacuation or access to resources (Iqbal et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Mulchandani et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn contrast, our data show that older participants in Akita exhibited lower levels of depression, anxiety, stress, and insomnia across most post-disaster periods.\u003c/p\u003e \u003cp\u003eThis reversal may reflect the moderate scale of the event and the absence of mass evacuation requirements.\u003c/p\u003e \u003cp\u003eUnlike catastrophic floods that disrupt living arrangements and social networks, the Akita rainfall allowed residents\u0026mdash;particularly older adults\u0026mdash;to remain within their familiar homes and communities, thereby preserving social continuity and perceived control.\u003c/p\u003e \u003cp\u003eAdditionally, the life-course perspective suggests that older individuals may possess stronger coping repertoires, accumulated through prior experiences with hardship or loss, which can buffer against stress in novel but non-life-threatening situations.\u003c/p\u003e \u003cp\u003eTogether, these findings imply that the psychological impact of a disaster depends not only on its physical severity but also on the degree to which it forces behavioral displacement and challenges established routines.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003eImplications for disaster mental health and policy\u003c/h2\u003e \u003cp\u003eThese findings highlight the need for both early and long-term psychosocial intervention following disasters, regardless of their physical magnitude. As shown in Table\u0026nbsp;2, psychological symptoms among the overall population gradually declined across the first post-disaster year, suggesting a certain degree of natural attenuation. However, Table\u0026nbsp;3 demonstrates that individuals who experienced any disruption to daily life, property, or housing continued to show elevated distress levels up to 12 months, indicating a persistent psychological impact among directly affected residents.\u003c/p\u003e \u003cp\u003eDisaster-response systems that allocate mental-health resources based solely on visible damage or casualty counts risk overlooking communities that experience enduring distress from disruption and uncertainty. Our 12-month data clearly show that psychological attenuation trails physical reconstruction. Therefore, municipalities should maintain accessible counseling, outreach, and peer-support programs for at least one to two years after an event. The collaboration with Akita Sakigake Shimpo demonstrates the practical value of community-based participatory approaches in identifying at-risk groups and sustaining engagement through local media.\u003c/p\u003e \u003cp\u003eAt a national level, the rising frequency of linear precipitation zones and extreme rainfall events in Japan (Yamada et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Kawaguchi et al. 2023) demands that mental-health perspectives be integrated into climate-adaptation policies.\u003c/p\u003e \u003cp\u003ePreparedness plans should explicitly include mechanisms for prolonged psychological monitoring and multi-year support for residents in newly affected regions.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003eLimitations and future directions\u003c/h2\u003e \u003cp\u003eSeveral limitations warrant consideration. First, web-based recruitment may have underrepresented residents without internet access or those experiencing severe hardship. Second, while the community survey provided valuable cross-validation, longitudinal follow-up of the same participants would better delineate causal pathways. Third, psychological data were derived from validated self-report scales rather than clinical interviews.\u003c/p\u003e \u003cp\u003eFuture work should combine repeated community assessments with objective indicators\u0026mdash;such as sleep, activity, or biological stress markers\u0026mdash;to clarify how \u0026ldquo;first-time disaster experiences\u0026rdquo; translate into chronic psychological sequelae.\u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eAlthough the 2023 Akita heavy rainfall caused only modest physical damage, it produced persistent and widening psychological disparities between affected and unaffected residents throughout the following year. The integration of repeated cross-sectional and community-based evidence underscores that even small-scale, moderate in physical magnitude yet unprecedented in local experience can impose lasting mental burdens that outlive physical recovery and reconstruction.\u003c/p\u003e \u003cp\u003eEffective disaster attenuation must therefore encompass not only infrastructure reconstruction but also long-term psychosocial support to restore community well-being. Even when physical scars fade, psychological wounds may remain\u0026mdash;particularly in regions unaccustomed to such climate-related disruptions.\u003c/p\u003e "},{"header":"Declarations","content":" \u003ch2\u003eContributions\u003c/h2\u003e \u003cp\u003eConception or design of the work: J.O., S.S., M.M.; Data cleaning: H.S., S.E.; Data analysis and interpretation: T.I., S.F.; Drafting the article: J.O., S.S.: Critical revision of the article: T.I., S.F.; Final approval of the version to be published: J.O., S.S., F.I., K.H. All authors read and approved the final manuscript.\u003c/p\u003e \u003ch2\u003eCompeting interests\u003c/h2\u003e \u003cp\u003eThe authors declare no competing interests\u003c/p\u003e \u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003e This research was supported by the Innovative Research Program on Suicide Countermeasures [Grant Number: JPSCIRS20220301], KAKEN Grant-in-Aid for Early-Career Scientists [Grant Number: 22K15780], and the International Research Institute of Disaster Science, Tohoku University.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eConception or design of the work: J.O., S.S., M.M.; Data cleaning: H.S., S.E.; Data analysis and interpretation: T.I., S.F.; Drafting the article: J.O., S.S.: Critical revision of the article: T.I., S.F.; Final approval of the version to be published: J.O., S.S., F.I., K.H. All authors read and approved the final manuscript.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe datasets generated and/or analyzed during the current study are not publicly available owing to privacy and ethical restrictions, but are available from the corresponding author upon reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAn, R., Qiu, Y., Xiang, X., Ji, M. \u0026amp; Guan, C. Impact of Hurricane Katrina on mental health among US adults. \u003cem\u003eAm. J. Health Behav.\u003c/em\u003e \u003cb\u003e43\u003c/b\u003e (6), 1186\u0026ndash;1199 (2019).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBryant, R. A. et al. Longitudinal study of changing psychological outcomes following the Victorian Black Saturday bushfires. \u003cem\u003eAust N Z. J. 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(2023).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYamada, T., Sato, T. \u0026amp; Nakamura, K. Characteristics of linear precipitation systems causing heavy rainfall in Japan. \u003cem\u003eAtmosphere\u003c/em\u003e \u003cb\u003e11\u003c/b\u003e, 1347 (2020).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003eTable 1 to 3 are available in the Supplementary Files section.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"climate change, extreme rainfall, mental health burden, repeated cross-sectional study, flood-naïve region","lastPublishedDoi":"10.21203/rs.3.rs-8495344/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8495344/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eClimate change is increasing the frequency of extreme rainfall events worldwide, yet evidence on their population-level mental health impacts\u0026mdash;particularly in regions with no prior flood experience\u0026mdash;remains limited. In July 2023, heavy rainfall caused widespread flooding in Akita Prefecture, Japan, a region historically unaccustomed to large-scale inundation.\u003c/p\u003e \u003cp\u003eWe 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\u0026ndash;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.\u003c/p\u003e \u003cp\u003eAt 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.\u003c/p\u003e \u003cp\u003eThese 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.\u003c/p\u003e","manuscriptTitle":"Persistent mental health burden following climate-change–related extreme rainfall: Repeated cross-sectional population surveys in a flood-naïve region of Japan","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-01-21 04:35:48","doi":"10.21203/rs.3.rs-8495344/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"editorInvitedReview","content":"","date":"2026-05-01T14:24:47+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"328046732549010076372565295081016188958","date":"2026-04-21T17:10:40+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-13T18:02:36+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"181764478386204093766032503125409083664","date":"2026-03-13T06:33:06+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"263207013890761257166818842451631297338","date":"2026-03-10T18:09:03+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-01-16T15:09:17+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-01-02T15:01:31+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-01-02T15:01:21+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2026-01-01T13:08:39+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"22a7a9e3-41ab-4249-9271-a88cfa0c3ff7","owner":[],"postedDate":"January 21st, 2026","published":true,"recentEditorialEvents":[{"type":"editorInvitedReview","content":"","date":"2026-05-01T14:24:47+00:00","index":123,"fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":61390718,"name":"Health sciences/Health care"},{"id":61390719,"name":"Biological sciences/Psychology"},{"id":61390720,"name":"Social science/Psychology"},{"id":61390721,"name":"Health sciences/Risk factors"}],"tags":[],"updatedAt":"2026-01-21T04:35:48+00:00","versionOfRecord":[],"versionCreatedAt":"2026-01-21 04:35:48","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8495344","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8495344","identity":"rs-8495344","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}