The GeoExtreme project, Module C: Changes in geohazard patterns based on climate models. Examples from case study areas

The aim for the present work is to establish models for evaluation of the effect of a changing climate on landslide and avalanche frequencies. Case studies have been carried out in four areas, all of them different with respect to topography, vegetation, climate and geology, and hence they experience different problems related to landslides and avalanches.
1) Large areas in the Southeastern part of Norway are covered by raised marine clays due to glacio-isostatic rebound, and a vast number of quick-clay slides have occurred here. We have studied the impact of expected increase in river discharge on potential quick clay slides.
2) The central South part of Norway is among the driest in the country, and our study area is located at the junction between two typical U-shaped valleys. Thick deposits of silt to sand dominated till cover the valley sides. Exposed schist bedrock is heavily weathered and act as a source for rock falls and soil development. Rare rainstorm events of extreme intensity have triggered flash floods, debris flows and shallow landslides in this region.
3) The fjord areas of Western Norway receive up to 4000 mm of precipitation pr year. Our study area in this region comprises a glacially carved and U-shaped valley close to sea level surrounded by mountain peaks up to 1800 m a.s.l. It is scarcely populated, but one of the main roads connecting eastern and western Norway runs through the valley. The study in this area mainly focuses on snow avalanches and rock falls.
4) Due to the alpine fjord landscape relatively large areas of the Troms municipality are situated in hazardous areas, involving snow avalanches, debris flows and rock falls. The community in this area grows extensively, and the pressure on land for construction purposes is pushing the limits into hazardous areas in the mountainsides.
A first approach has been to describe the present hazard level. Individual hazard zonation maps have been made for avalanches, debris flows, rock falls and quick clay slides respectively. The hazard zonations are based on input from mapping of colluvium and source areas, modelling of susceptibility for shallow landslides and modelling of potential avalanche- and rock-fall runout distances
. To address the impact of future climate changes, a parallel set of zones reflect the future hazard level. Downscaled climate scenarios produced by the work in Module B are crucial input to this latter modelling.
The final step of the evaluation is an extrapolation of the results to a regional level.