Evaluating the effect of digital elevation model resolution in lahar hazard simulations: insights from the 1877 Cotopaxi scenario, Ecuador

Abstract

Numerical simulations of gravity-driven flows such as lahars are highly sensitive to the Digital Elevation Model (DEM) used, which directly affects prediction fidelity and computational demands. In this study, we explore the influence of DEM upscaling on lahar simulations within the topographically-complex northern Cotopaxi drainage network (∼70 km length). We utilize the 1877 lahar-scenario, the Kestrel dynamic-based simulator parameterised for lahars (known as LaharFlow), and a 3-meter DEM upscaled to 10, 15, 20, and 30 m. Our results reveal that coarser DEMs inevitably smooth topography, resulting in shallower and wider channels compared to reality, which redistributes flow volume laterally. This effect causes the 30-meter DEM to overestimate inundation areas by 58% compared to 10-meter DEM, while underestimating average maximum flow depth by −47.1% and speeds by −29.8%. Flow parameters such as maximum inundation distance and propagation speed showed limited sensitivity (