DEM resolution effects on shallow landslide hazard and soil redistribution modelling

Abstract

AbstractIn this paper we analyse the effects of digital elevation model (DEM) resolution on the results of a model that simulates spatially explicit relative shallow landslide hazard and soil redistribution patterns and quantities. We analyse distributions of slope, specific catchment area and relative hazard for shallow landsliding for four different DEM resolutions (grid sizes of 10, 25, 50 and 100 m) of a 12 km2 study area in northern New Zealand. The effect of DEM resolution is especially pronounced for the boundary conditions determining a valid hazard calculation. For coarse resolutions, the smoothing effect results in a larger area becoming classified as unconditionally stable or unstable. We apply simple empirical soil redistribution algorithms for scenarios in which all sites with a certain landslide hazard fail and generate debris flow. The lower initial number of failing cells but also the inclusion of slope (limit) in those algorithms becomes apparent with coarser resolutions. For finer resolutions, much larger amounts of soil redistribution are found, which is attributed to the more detailed landscape representation. Looking at spatial patterns of landslide erosion and sedimentation, the size of the area affected by these processes also increases with finer resolutions. In general, landslide erosion occupies larger parts of the area than deposition, although the total amounts of soil material eroded and deposited are the same. Analysis of feedback mechanisms between soil failures over time shows that finer resolutions show higher percentages of the area with an increased or decreased landslide hazard. When the extent of sites with lower and higher hazards are compared, finer grid sizes and higher landslide hazard threshold scenarios tend to increase the total extent of areas becoming more stable relative to the less stable ones. Extreme care should be taken when quantifying landslide basin sediment yield by applying simple soil redistribution formulas to DEMs with different resolutions. Rather, quantities should be interpreted as relative amounts. For studying shallow landsliding over a longer timeframe, the ‘perfect’ DEM resolution may not exist, because no resolution can possibly represent the dimensions of all different slope failures scattered in space and time. We assert that the choice of DEM resolution, possibly restricted by data availability in the first place, should always be adapted to the context of a particular type of analysis. Copyright © 2005 John Wiley & Sons, Ltd.