Comparative analysis of shoreline dynamics in Surabaya and Sidoarjo under climate variability

This study investigates the influence of hydroclimatic variability on shoreline dynamics along two contrasting coastal systems in East Java, Indonesia, Surabaya’s engineered urban coast and Sidoarjo’s natural tidal-flat coast, during 2015–2025. Shorelines were extracted from multi-temporal Landsat imagery using NDWI, shoreline change rates were calculated with DSAS, and rainfall data from BMKG were correlated with mean End Point Rate (EPR) to assess hydroclimatic impacts on coastal morphodynamics. Results reveal contrasting shoreline trajectories driven by coastal typology. Surabaya exhibits semi-cyclic shoreline adjustments controlled by reclamation barriers and restricted sediment pathways, resulting in localized accretion despite declining rainfall. In contrast, Sidoarjo shows rainfall-responsive erosion–accretion cycles, where open tidal channels enable rapid sediment redistribution during high-rainfall periods. Rainfall–EPR correlations are strong at the local scale (r = 0.76 in Surabaya; r = 0.80 in Sidoarjo) but weak when aggregated (r ≈ 0.10). This indicates that integrating hydroclimatic indicators with geomorphic context does not increase overall correlation strength, but improves interpretation of typology-specific shoreline responses obscured in aggregated analyses. The NDWI–DSAS–rainfall workflow provides a scalable framework for monitoring shoreline dynamics in tropical monsoonal environments.