Climate-related disasters increasingly threaten over one-third of the global population, specifical communities within 100 km of coastal zones. Indonesia, the world’s largest archipelago with the second-longest coastline, faces tidal (Rob) flooding from high tides, land subsidence, and sea-level rise. This study assess fish farmers’ vulnerability to Rob flooding in Java’s Indramayu District. Our Social Vulnerability Index (SoVI)’s development involved 150 questionnaires, focus group discussion, and key-informant interviews between 16 and 20 October 2019. It found a high vulnerability, a SoVI score of + 1.76 comprising nine principal components (PCs): external support and government mitigation, local knowledge, income, expenditure, family size, seasonal-expenditure, education, experience, and ethnicity. Contributing to ‘vulnerability’ and ‘resilience’ concepts, it highlights community memory of repeated disasters and its impact on local adaptive capacity. Findings inform policymakers to address the PCs influencing vulnerability, including critically-needed livelihood support and early-warning systems relevant to the country’s 12,000 + coastal-villages and developing countries where over 90% of fishermen live. © 2022, The Author(s).