Flood monitoring and damage assessment in agricultural field using Sentinel-1 SAR data in Gumara river catchment, Blue Nile basin

Floods are one of the most severe natural hazards worldwide causing extensive damage to lives, property, and resources. Annually, riverine floods along the Gumara River catchment consistently destroy agricultural lands. This study aims to monitor floods primarily using Sentinel-1 SAR satellite data in the Gumara River catchment. Sentinel-1 SAR data provides essential temporal resolution and backscatter values for monitoring flood damages. Sentinel-1 SAR images from July 11th, 23rd, and August 4th, 2021 were used for flood extent analysis employing histogram-based thresholding technique. Different factors such as land use/cover, slope, elevation, soil, and flood depth were considered as criteria for flood hazard mapping with Analytical Hierarchical Process (AHP). Using weighted overlay analysis, the flood hazard layer was combined with land use/land cover data to produce flood risk maps in a GIS environment. The study’s findings indicated that the flood extent increased significantly from July 11th to August 4th, with the August 4th flood events covering an area of 11.97 km². Agricultural land (59.63% of study area) was the most affected with 7.48 km² inundated during the August 4th flood event. The flood hazard analysis indicated that 5.40%, 30.0%, 27.0%, 25.0%, and 12.7% of the Gumara catchment were subjected to very low, low, moderate, high, and very high flood hazards, respectively. The flood risk map showed that 10.10%, 40.8%, 21.2%, 20.14%, and 7.60% of the area were in very low, low, moderate, and very high flood risk zones, respectively; 12.02% and 21.75% of agricultural land fall within very high flood risk zones. Severely affected areas with flood hazard and risk levels are Wagetera, Kidist Hana, Bebeks, Shina, Mtslina Tana, Zarina Jegina, and Gere Gera Gedam Eyesus. Generally, the downstream parts of the Gumara River catchment, characterized by flat slopes and low elevation, are at very high flood hazard and risk levels. The study suggests flood monitoring and mitigation strategies like early warning systems, land-use zoning, embankments should be implemented to protect Agricultural lands and support sustainable farming practices.