Urban flood hazard in the context of rapid urban growth in the Kathmandu Metropolitan City, Nepal

The increasing complexity of urban expansion and its impact on hydrology is significant, especially in densely populated regions. We conducted this study in the Kathmandu Metropolitan City (KMC), Nepal. The KMC is an essential urban center with many essential amenities and opportunities compared to other cities in Nepal. Due to its abundant facilities, the city attracts thousands of people from different parts of the country each year, and experiencing rapid urban expansion. This rapid urban expansion, which involves annual increases to paved and impervious surfaces, has resulted in significant impacts on urban hydrology. Impervious materials partially seal the surface, significantly reducing water infiltration. Thus, urbanization increases the speed and amount of surface runoff. As a result, the city gets inundated every monsoon, impacting thousands of people. We aimed to conduct flood hazard assessments under continuous urbanization using an Analytical Hierarchy Process (AHP) integrated with Geographic Information Systems (GIS). The study revealed that land use/land cover and distance from the river were significant factors contributing to urban flooding, while the type of soil was the least important contributing factor. The core region of the city is in the “very high” to “high” risk zone, while fringe areas are in the “medium” to “low” risk zone.