HISTORICAL AND FUTURE SHORELINE CHANGES AND SEA LEVEL RISE IMPACTS ON RIVERINE FLOODING IN EAST KALIMANTAN, INDONESIA

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 Beaches in East Kalimantan have been experiencing erosion, and rising sea levels driven by climate change are predicted to exacerbate this trend. This study investigates historical shoreline changes using the Digital Shoreline Analysis System (DSAS), evaluates the impacts of sea level rise under IPCC (Intergovernmental Panel on Climate Change) Sixth Assessment Report scenarios on future shoreline retreat using the Bruun rule approach, and simulates riverine flooding in the Penajam Paser Utara Regency. Historical shoreline data were derived from the Normalized Difference Water Index (NDWI) raster based on Landsat 5, 8, and 9 satellite imagery. Flood inundation simulation was performed based on a rainfall-runoff model with unsteady flow simulations, considering a 25-year return period rainfall. From 2005 to 2024, the most severe shoreline retreat was observed in the Samboja District (EPR: -15.49 m/year), while the Longkali District experienced the lowest retreat (EPR: -1.84 m/year). In future projections, beaches in South Balikpapan District are projected to experience the highest relative beach loss, whereas the least was observed in Samboja District, owing to its wider beach profiles. Flood inundation areas and depths are projected to consistently increase with more extreme climate scenarios and longer projection periods. The maximum inundated area (6,643.4 ha) occurred under the SSP5-8.5 scenario for 2150, while the smallest inundation area (3,649.7 ha) was simulated under the SSP1-2.6 scenario for 2050. These findings underscore the urgent need for adaptive coastal mitigation in East Kalimantan coastal areas, providing valuable insights for regional planning and flood mitigation in the Penajam Paser Utara Regency, the site of Nusantara.