Flood Hazard Analysis and Risk Assessment of Koshi River, Bihar (India) using Remote Sensing, GIS and AHP Techniques

Rising flooding, which is exacerbated by both climate change and human behavior, demands proper identification of vulnerable zones. Conventional hydrological analysis can neglect geographical variability. In this study, a combined geospatial and decision-making process is used to determine the levels of vulnerability and risk of flooding in the Koshi River Basin in the state of Bihar.  The research work has developed a susceptible, vulnerable and risk map by integrating GIS, Remote Sensing and AHP. Weightings of eleven physical and hydrological factors and five socio-economic indicators were carried out in a systematic manner using a multi-criteria decision-making framework that allowed appropriate consideration of their relative contributions to flooding. Flood susceptibility, vulnerability and risk maps were created using the GIS environment's Weighted Overlay technique. According to the analysis, population density (41.6%) and literacy rate (24%) are controlling factors for flood vulnerability in the basin, whereas rainfall (23.9%), elevation (14.7%) and drainage density are the main elements that influence flood susceptibility. The Koshi basin is largely covered by the low and moderate classes of flood susceptibility, whereas a very minor amount (0.03%) comes under the high susceptibility classes, according to results from flood susceptibility maps. A significant section (42.87%) of the basin has moderate flood susceptibility due to a combination of exposure and socioeconomic characteristics, according to the results of the flood vulnerability analysis. According to the flood risk results, a significant amount of the basin (84.18%) has moderate flood risk, while a tiny portion has high flood risk in the low-lying, heavily inhabited areas close to the basin's riverbanks.  ROC-AUC for model validation yielded an accuracy of 66.3% and proved that the proposed GIS-AHP model was a reliable. Conclusion from this study underscore an integrating role in both physical and socio-economic considerations with prospects of enhancement through climate scenarios in flood mitigation and planning/early warning maps.