Integrated optical and SAR data analysis for the monsoonal flood hazard mapping in the Tawi Basin Northwest Himalaya

Monsoon forcing significantly impacts flood hazards, intense and prolonged monsoon rains exacerbate flood risks by rapidly increasing river discharge and overwhelming drainage systems, especially in regions with unplanned infrastructure or altered land use. In the study, to define Flood Hazard Zonation (FHZ) in terms of risk assessment, the Analytical Hierarchy Process (AHP) technique was employed to integrate different thematic layers and ascertain the relative importance of criteria in the Geographic Information System (GIS) environment. The FHZ results shows that 103.81 Km² (3.50 %) of the region was classified as very high-risk by the FHZ, while 617.17 Km² (20.82 %), 865.87 Km² (29.21 %), 1119.42 Km² (37.77 %), and 257.73 Km² (8.70 %) were classified as high-risk, medium-risk, and low-risk. Further, Synthetic Aperture Radar (SAR) based backscatter images of the floodwater area were demarcated for two periods in order to validate the FHZ area based on GIS data. Furthermore, an inundation region of roughly 216.37 km² was revealed by pre-processing SAR data, change detection analysis of pre-flood photos, flood-image thresholding, and the creation of flood inundation maps using Google Earth Engine (GEE). The findings showed that flood hazard evaluations, mitigation strategies, and quick post-flood management could be achieved with the help of both optical and SAR-based techniques.