Flash flood susceptibility modelling using geomorphometric approach in the Ushairy Basin, eastern Hindu Kush

This study focuses on flash floodsusceptibility modelling using geomorphometricranking approach in the Ushairy Basin. In the study area, flash floodsare highly unpredictable and the worst hydrometeorologicaldisaster. An advanced spaceborne thermal emissionand reflection radiometerglobal digital elevation model was used as input data in a geographic information system environment to delineate the target basin. A total of 17 sub-basins were delimited using a threshold of \(4 \hbox {km}^{2}\). The attribute information of each sub-basin was analysed to compute the geomorphometricparameters by applying Hortonian and Strahler geomorphological models. The results were analysed and categorised into five classes using statistical techniques, and the rank score was assigned to each class of all parameters depending on their relation with flash floodrisk. In this study, 16 parameters were analysed to quantify the geomorphometricnumber of each sub-basin depicting the degree of flash floodsusceptibility. The geomorphometricnumber of each sub-basin was linked to the geo-database for spatial visualisation. The analysis reveals that extremely high, very high, high and moderate sub-basins susceptible to flash floodswere spread over an area of 55%, 8.5%, 23.7%, and 11.5%, respectively. It was found that out of total settlements, 53% are located in the extremely highly and very highly susceptible sub-basins. In the study area, the upper reaches are characterised by snow-covered peaks, steep slopes and high drainage densities(\({>}1.7 \hbox { km/km}^{2})\). The analysis further indicated that the flash floodsusceptibility increases with the increase in area, relief and relief ratioof the sub- basins. Modelaccuracy was assessed using primary data regarding past flood damages and human fatalities. Similarly, socio-demographic conditions of each sub-basin were also compared and linked to the extent of flash floodsusceptibility. This study may assist the district government and district disaster management authority of Dir upper to initiate flood risk reduction strategiesin highly susceptible zones of the Ushairy Basin.