Fuzzy Tsukamoto-GIS Framework with Pixel-Level SAR Validation for Flood Susceptibility

Abstract

Physical flood susceptibility in Cepu Subdistrict is shaped by low relief, proximity to the Bengawan Solo River, land-cover conditions, soil permeability, river density, and seasonal rainfall. This study applies a documented Fuzzy Tsukamoto-GIS workflow to estimate physical flood susceptibility across 17 villages using six parameters: slope, elevation, soil permeability, monthly rainfall, land use, and river density. Susceptibility scores range from 0.440 in Mulyorejo to 0.765 in Kapuan. Validation uses two approaches: pixel-level Sentinel-1 SAR imagery for the February 2022 flood event, and village-level rank comparison with BPBD flood records (2018-2023). Pixel-level validation shows strong performance with overall accuracy of 93.85%, ROC-AUC of 0.876, Spatial Kappa of 0.708, CSI of 59.08%, and FAR of 32.42%. Village-level Spearman correlation (ρ = 0.990, p < 0.001) confirms consistency with reported flood frequencies. Sensitivity analysis identifies monthly rainfall (SI = 0.28) and land-use susceptibility (SI = 0.24) as the most influential parameters. Cross-referencing BPBD records with media reports revealed potential reporting bias in Mulyorejo, highlighting the value of SAR-based validation. The pixel-level susceptibility map can support mitigation prioritization and spatial planning while providing a transparent basis for further calibration. This study assesses physical susceptibility rather than comprehensive vulnerability, as socioeconomic and coping capacity dimensions are not included.