Flash Flood Hazard Mapping Using Landsat-8 Imagery, AHP, And GIS In The Ngan Sau And Ngan Pho River Basins, North-Central Vietnam

Flash floods have been blamed for significant losses and destruction all around the world are widely, including Vietnam, a developing nation that has been particularly hard hit by climate change. Therefore, flash flood hazards are essential for reducing flood risks. The topographic wetness index (TWI), altitude, slope, aspect, rainfall, land cover, normalized difference vegetation index (NDVI), distances to rivers and roads, and flow length were used in this study to create a spatial database of ten exploratory factors influencing the occurrence of flash floods in the Ngan Sau and Ngan Pho river basins (North-Central Vietnam). Subsequently, the analytic hierarchy process (AHP) was applied to calculate the weights of these influencing factors. The flood threat was then mapped using GIS techniques. The validation of the flash flood hazards involved 151 flood inventory sites in total. The findings demonstrate that (i) distance from rivers (0.14) and TWI (0.14) factors have the greatest influence on flash flooding, whereas distance from roads (0.06) and NDVI (0.06) factors were found to have the least influence; (ii) a good conformity of 84.8 percent between flood inventory sites and moderate to very high levels of flash flood hazard areas was also discovered; (iii) high and very high flood hazard levels covering areas of 275 and 621.1 km2 were mainly detected along and close to the main rivers and streams, respectively. These results demonstrated the effectiveness of GIS techniques, AHP, and Landsat-8 remote sensing data for flash flood hazard mapping.