In recent decades, the frequency and severity of extreme, multi-hazard natural events have significantly increased. This escalation has become especially pronounced in recent years and is projected to intensify further due to climate change. Many of these hazards are closely linked to hydrological processes, including floods, mudslides, landslides, avalanches, and tsunamis. Advances in numerical methods, together with a growth in computational power, have driven the widespread adoption of simulation tools to better understand and predict these complex events. Techniques such as shallow water models, advanced finite element and finite volume schemes, and in particular particle-based methods, including Smoothed-Particle Hydrodynamics (SPH), Discrete Element Method (DEM), Material Point Method (MPM), and Particle Finite Element Method (PFEM), enable coupled simulations of natural hazards. Their efficient parallelization on CPUs and GPUs further supports large-scale, three-dimensional modelling efforts. This thematic session aims to showcase recent progress in the numerical simulation of natural hazard initiation and dynamics, fostering collaboration and dialogue among researchers and practitioners, exploring and discussing how fully three-dimensional methods (or advanced numerical methods) can both complement and ultimately transition beyond classical one-phase depth-averaged approaches in hazard assessment. While emphasizing hydrological hazards, the session welcomes contributions on numerical modelling of a broader range of natural phenomena—geological and meteorological alike—with particular interest in multi-hazard interactions (e.g., landslides triggered by earthquakes, tsunami waves induced by landslides). Additionally, studies addressing fluid-structure and fluid-soil-structure interactions, reflecting the interplay between natural hazards and civil infrastructure, are highly encouraged.