Modelling increasing natural-hazard risk due to urban growth in Kathmandu Valley, Nepal

In our rapidly urbanizing world, many hazard-prone regions face significant challenges when it comes to risk-informed urban development. This study specifically addresses this issue by investigating evolving spatial interactions between natural hazards, ever-increasing urban areas, and social vulnerability in Kathmandu Valley, Nepal. The methodology used in this work considers: (1) the characterization of flood hazard and liquefaction susceptibility using pre-existing global models; (2) the simulation of future urban built-up areas using the cellular-automata SLEUTH (Slope, Land use, Excluded areas, Urban extent, Transportation, Hillshade) model, which requires satellite imagery for statistical calibration and validation; and (3) the assessment of social vulnerability using a social vulnerability index tailored for the case-study area. Results show that the total built-up area in Kathmandu will increase to 352 km² by 2050, which is effectively double the equivalent 2018 figure of 177 km². The most socially vulnerable villages will account for 29% of the total built-up area in 2050, which is 11% more than their current proportion. Built-up areas in the 100-year and 1000-year return period floodplains will respectively increase from 38 km² and 49 km² today to 83 km² and 108 km²in 2050. In the same time frame, built-up areas in liquefaction-susceptible zones will expand by  13 km² to 47 km². The results of this study illustrate how, where, and to which extent risks from natural hazards can evolve in socially vulnerable regions. Ultimately, this study emphasizes an urgent need to implement effective policy measures (e.g., land-use regulations) for reducing tomorrow's natural-hazard risks.