| 07 Sep 2026
Landslide debris inundation risk and uncertainty from a process-based hazard model for the West Coast region of New Zealand
Abstract. Regional landslide debris inundation risk assessments are commonly constrained by scenario-based formulations that require explicit enumeration of landslide sources and runout events, limiting scalability and introducing sensitivity to subjective modelling choices. This study presents a process-based framework for regional landslide debris inundation risk assessment that employs a flux-based hazard metric to quantify probability of inundation and mean annual property loss risk.
The approach builds on the Landslide Source-to-Inundation Process Model by coupling spatially distributed landslide sediment production with mass-conservative downslope routing, and converting resulting debris flux into probabilistic estimates of building damage. Risk is evaluated as a temporally integrated quantity arising from all feasible landslide sources, volumes, triggers, and return intervals, without reliance on discrete runout scenarios. We apply the method to the ~25,000 km2 West Coast region of New Zealand. Results indicate the aggregate rainfall-induced property loss corresponds to approximately 1.6 equivalent complete residential-building losses per year under present-day conditions. Under the RCP6 2081–2100 climate scenario, rainfall-induced residential APLR increases by approximately 50 %, assuming landslide sediment production increases in proportion to rainfall-induced susceptibility.
Uncertainty is quantified through parametric sensitivity analysis, Monte Carlo simulation, and evaluation of topographic resolution effects. Combined uncertainty is estimated at approximately ±1.0 OOM at the 1-sigma-equivalent level for the regional 25 m model; a conservative ±1.25 OOM uncertainty is adopted for interpretation. This reduces substantially when higher-accuracy topography is employed. The framework provides a scalable and transparent basis for regional landslide risk analysis and supports risk-informed planning in landslide-prone regions.
The authors outline an interesting debris flow/inundation risk modeling approach, in which the many disparate components have been thoughtfully considered. In particular, the authors pay careful attention to elements of uncertainty, which is a great strength to this work. While complex, the authors are efficient in their explanations of their modeling method and the outcomes. I would recommend publication with some minor considerations:
There are some acronym re-definitions at the beginning of the methodology and in the conclusions. I do welcome the conclusion re-definitions, otherwise consistency may be better as well as yielding to any journal guidelines.
The frequent reference to recent work by the authors corresponds to both submitted works as well as reports. I am understanding to both moving findings into peer-review and the nature of work that quickly builds on itself. The references I read appear to have similar topics of work but this manuscript adds to those works in meaningful ways. In this way, these references in methodology discussions are essential and enough relevant detail is carried through between the methodology and appendices. My suggestion here is that it would greatly bolster this work to add references to sections like results and discussion either from their prior work or that generally conveys similar outcomes that the authors are.