A Sentinel-1 SAR Based Methodology for Flood Mapping and Strengthening Croatia’s Flood Response through Space-Based Cooperation

The March 2025 flooding in Slavonia underscored both the urgency of timely geospatial intelligence and the limitations of fragmented national response systems. This article introduces a practical methodology for flood extent detection using Sentinel-1 synthetic aperture radar (SAR) data, employing the Normalized Difference Sigma-Naught Index (NDSI) derived from VV-polarized backscatter to extract the flooded areas. The results highlight SAR’s unique value in supporting rapid flood assessment for emergency management. Yet the analysis also reveals a broader systemic issue: technological tools alone are insufficient without institutional synergy. To bridge this gap, we propose that Croatia’s accession to the International Charter: Space and Major Disasters represents a strategic step forward. Such integration would not only secure timely satellite data access but also catalyze national coordination among military, civil, academic, and commercial actors in disaster risk management.