Types of coastlines and the evacuees’ mental health: A repeated cross-sectional study in Northeast Japan

Although the health risks and benefits of coastal areas have long been researched, these effects of the different types of coastlines have rarely been explored on the evacuees living near the coast, in a post-disaster context. Thus, this study aimed to explore, with the passing of years after a disaster, what kind of coastline is a useful public health resource as a post-disaster reconstruction approach in coastal environments that have suffered significantly from the tsunami disaster in northeast Japan in 2011. This study compared the evacuees' mental health based on proximity to the coast and the types of coastlines (artificial, semi-natural, and natural). Data were drawn from the Miyagi Prefectural Government surveys, which targeted almost all evacuees of the 2011 Great East Japan Earthquakes and Tsunami (n = 96,203). We applied a pooled Poisson regression model to a repeated cross-sectional dataset of evacuees' mental health between 2012 and 2016. Moderate psychological distress, measured via the Kessler Psychological Distress Scale (K6) score, was the dependent variable, while proximity to the coast and type of coastline were the independent variables. The estimated main effects of type of coastline indicated that overall associations between K6 ≥5 and all types of coastlines within a 1.6 km buffer of participants' residential space were not statistically significant (p > 0.05). However, among types of coastlines, the interaction terms of semi-natural coastline × year (2015 and 2016) were significantly associated with lower incidence rate ratios (IRR), which decreased in 2015 and 2016 (IRR: 0.88, 95%CI: 0.79–0.98; IRR: 0.78, 95%CI: 0.68–0.90, respectively). Further, we computed the marginal effects of coastline types for each year to observe differences in the impact on moderate psychological distress depending on different accessible coastline types within a distance of 1.6 km from the participants’ living space. We found that, after the revision of the coastal act in 2014, the moderate mental stress of participants who lived around semi-natural coastlines significantly tended to be low (dy/dx: −0.04, 95%CI: −0.08–0.01 in 2015; dy/dx: −0.07, 95%CI: −0.11–0.04 in 2016). This finding can encourage policymakers to manage coastal areas with green infrastructure in the post-disaster reconstruction sustainably.