Avalanche simulations are a common tool for hazard assessment in various operational settings. Simulation input as material parameters or initial conditions, are mainly determined via guidelines and back calculations. Currently the values of input parameters do not include ranges. However good operational practise may include the investigation of multiple possible scenarios and the corresponding result variability.

To directly assess and quantify this variability we introduce parameter variations in avalanche simulations. Evaluating the sensitivity of simulated run out lengths, allows us to determine “run-out gradients” indicating how sensible the run-out length is to simulation input changes. We quantify parameter ranges of the process parameter µ (friction) and release depth d_ref,, trying to resemble the result variability of a classical scenario variation.

In a next step we introduce an explicit uncertainty treatment. For a set of ~10 avalanche paths we determine parameter ranges that resemble scenario limits originating in variations of total flow mass due to a changed initial release volume and entrainment.

These parameter ranges are subsequently used to display a frequency distribution. This allows us to obtain an overview of the spatial distribution of the run-out and to determine the variation of the maximal velocity within this bandwidth of simulations. With these results it is possible to identify areas where large result variability or certainty can be expected. Our approach provides another step towards the application of probabilistic methods in mass flow simulations. 

Gobiet is a former climate modeler and works since 2014 as operational avalanche forecaster. With his modelling background, he was puzzled by the lacking exploitation of models in most operational avalanche services and started to explore this potential. Since 2018 V. Hatvan develops together with A. Gobiet a model system, consisting of weather- snow- and avalanche dynamics models, combined with observations to assess and predict local avalanche danger. In addition, they implement the detailed snow model SNOWPACK for the operational use in the avalanche service of Styria, Austria. The interest and expertize of V. Hatvan and A. Gobiet particularly the exploitation of models and model systems in an operational context, rather than the detailed modeling of processes.

Model-aided assessment and prediP local avalanche hazards

V. Hatvan, A. Gobiet

In the framework of the Interreg SI-AT project “CROSSRISK” (Public warnings – reducing rain and snowfall related risks) a model system to assess and predict local avalanche danger is developed. It is aimed to assist local authorities in their regular assessment of the necessity of road closure, ski slope closure and evacuations. This contribution describes the basic concept of the model system, which consist of several model- and observational components and aims to integrate various sources of information to optimally assess avalanche danger in a local context.

Glacial lake outburst floods (GLOFs) are serious disasters in glacial areas. At present, glaciers are retreating while glacial lake area and the outburst risk increases due to the global warming. Therefore, the research of early warning method of GLOFs is important to prevent and reduce the disasters. This paper provides an early warning method using the temperature and rainfall as indices. The daily growth rate of positive antecedent accumulative temperature and the antecedent thirty days accumulative precipitation are calculated for 21 events of GLOF before 2010, based on data from the 21 meteorological stations nearby. The result shows that all the events are above the curve, which can be taken as the early warning threshold curve. This has been verified by the GLOF events in the Ranzeaco glacial lake on 2013-07-05.

Today, research that aims at better mitigating avalanche risk remains dominated by a deterministic culture led by physical approaches. As a striking example, the impressive number of existing avalanche numerical codes is to be compared to the relative poverty of probabilistic attempts in this field. However, all physically-based models available for hazard assessment must still be locally calibrated to provide robust predictions of the high-return-period events required for land use planning. Second, beyond the sole question of uncertainty due to insufficient calibration, high-return-period events are truly probabilistic concepts, which is imperfectly acknowledged by many engineering approaches still based on deterministic rules of thumb. Third, even a “perfect” avalanche model cannot define a unique event corresponding to a given return period and mitigation approaches should nonetheless consider elements at risk explicitly to define land-use strategies integrating, e.g., budgetary constraints and risk perception by citizens and stake-holders. Finally, the assumption of stationary conditions inherent to all engineering procedures existing in this field may be wrong, i.e. there exist safe zones that may become dangerous and existing defense structures ineffective. On this basis, our work develops a comprehensive framework for the manipulation of the probabilistic and uncertainty concepts underlying hazard and risk mitigation allowing i) proper consideration of elements at risk and behavior towards risk and ii) acknowledgement of potentially strong non-stationarities. This is achieved by combining statistical extreme value theory, spatio-temporal models, probabilistic-numerical mass movement models and formal risk assessment taking elements at risk into account by merging the contributions of various disciplines within a Bayesian context. This contribution will share our experience and approach with the community, as a basis for the development of improved mitigation strategies in land-use planning.

Mountainous regions are highly sensitive to climatic changes. The warming trend of the last decades and the related retreat of glaciers and permafrost consequently imply strong changes regarding sediment transport patterns due to intensive melting and the (re-)activation of potential sediment sources. The present study aims to present a holistic approach to analyze sediment cascades in this climatic and geomorphological context.

The study area, the partly glaciated Solda / Sulden catchment in the area of Val Venosta / Vinschgau (Italian Alps), was mapped geomorphologically to define the spatial distribution of source, transport and deposition areas. Subsequently, potential sediment pathways between topographically connected geomorphological landforms form the base to analyse the network of transport processes within the catchment in detail. The identification of spatial and temporal hot-spots as well as triggering factors of these sediment transport processes will be obtained by combining the results of the network analysis with results of DEMs of Difference (DoDs) representing different time intervals (months/years). Furthermore, measurements of fluvial sediment transport play an important role to qualitatively validate the findings. The monitoring combines regularly conducted direct measurements of both bedload and suspended sediments and continuous indirect measurements (e.g. geophones, turbidimeters). Sampling points are located at glacier outlets, in the proglacial river and at the outlet of the catchment.

Finally, based on the overall result of the study, the significance of extreme meteorological events, like heavy rain storms or heat waves, for the intensity and spatial distribution of sediment transport will be estimated to outline potential risks for infrastructure or population.

Since 2014 the applicant Kay Helfricht, PhD is associated at the IGF/ÖAW conducting research in the key areas of remote sensing of the cryosphere, applied geophysics in glaciology, glacier mass balance measurements and mountain hydrology.

Since two years he focusses on the physical processes causing increasing rockfall activity subsequent glacier downwasting in the framework of the project “GlacierRocks - Glacier-Headwall interaction and its influence on rockfall activity”. As a logical continuation of this research effort, the ÖAW Earth System Sciences project “Hidden.ice - Changing debris cover on Eastern Alpine glaciers: Quantification and hydrological impacts.” (Start May 2019) tackles the impact of increasing debris deposits in the transition zone from glacier ice to proglacial areas.Thus, his work focusses on climate change impacts on fluvial processes and natural hazards.

He will contribute to the discussion by presenting planned observations of sediment dynamics in paraglacial areas, and by developing answers to changes in sediment dynamics in mountain regions caused by climate change.

Hidden.ice - Changing debris cover on Eastern Alpine glaciers: Quantification and hydrological impacts

Since the Alps have faced a period of rising temperatures over the past 150 years, high mountain environments have undergone a dramatic change. Deposited supraglacial debris terminates at the current glacier tongues and accumulates to layers of several centimetres thickness. Currently no general assessment exists on the present state and recent evolution of debris cover on glacier surfaces in Austria. Little is known about how readily sediment loosened through permafrost degradation higher in the basin is coupled with the channel network, and there is little historical research on how fluvial systems from debris-rich proglacial areas might have changed over time.

The Hidden.ice project aims to deepen our knowledge on actual debris cover on glaciers in Austria, its effect on ice ablation, and its connectivity to fluvial transport, with a focus on the processes of debris deposition and renewed movement directly at the current glacier tongues. The hydrological impact of increasing debris deposits in the transition zone from glacier ice to proglacial areas will be tackled by investigating

(i) where and to which extent Austrian glaciers are faced with increasing debris cover,

(ii) which the long-term effects of debris cover on glacier mass balance and on the existence of proglacial ice are,

(iii) how the supraglacial debris is connected to fluvial transport and

(iv) how renewed movements of sediment and the channel network evolve in the proglacial area of partly debris-covered glaciers over time.

The transition zone from glacier ice to proglacial areas will be drawn from the combination of expertise in glaciology, hydrology, geomorphology, environmental earth observation and documentation of historic conditions of fluvial processes, all covered by the team of researchers from five institutions in Austria and Germany.

In the Alpine region, flash floods and debris flows represent a major hazard for infrastructures and human life. Starting from the 1960s, many efforts and investments have been devoted to build torrent control structures such as check-dams and retention basins, based on a safety and control paradigm relying on technical solutions. Recent debris-flow events in Italy highlighted how the combination of an extreme event with the lack of structures’ maintenance can result in an enhanced risk for the population.

The current climatic change represents a further challenge for the design of new torrent control structures. The increase of extreme climatic events, such as heavy rain storms or heat waves resulting in prolonged draughts, would affect for the intensity and spatial distribution of floods. The joint effect of glacier retreat and permafrost degradation is expected to increase sediment delivery and remobilization from rock walls, glacier forefields, and rock glaciers.

Today, the development of warning systems based on real-time detection of torrential flows with compact and low-cost sensors has spurred a great deal of interest. Their application can be particularly effective in both semi-natural, highly frequented stream reaches (e.g. for canyoning) and in anthropized valleys and fans where structural mitigation measures alone are not reckoned sufficient. In this work, we explore the potentials and limitations of automatic detection systems for flash floods and debris flows in sites of Northeastern Italy in an integrated risk management approach.

For the critical investigation to find out if old protection measures correspond to present conditions in torrent-catchments and for the adaption to future developments (e.g. case-of-overload), "Integrated torrential development concepts" will prospectively be developed for relevant torrents in Bavaria. Within these concepts, the treatment of the protection system is divided into four different levels of consideration: protection system (1), function groups (2), structural measure (3) and construction parts (4).

In the first level, the current protection system has to be analysed and assessed in a holistic way concerning past and future developments. It is necessary to figure out what the initial purpose of the constructions was, whether their function is still needful or not and if they can withstand future events. In addition, the present and future boundary conditions for the further planning have to be defined.

In the second level, the key-processes, -functions and -activities have to be identified and combined to functional sections. For these sections different measures (technical/bioengineering/organisational) have to be detected. All measures with the same function in one section form a function group. To cope with the case-of-overload it is necessary to take interactions between all measures into account.

The third level has the focus on the structural measure. Based on the preliminary works the current state and the initial function of the construction and the functions to be fulfilled are given. For the handling of constructions, the following options are possible: adoption, rehabilitation, optimisation, new construction/replacement measure, deterioration/renaturation.

In the fourth level, the design of a single structural measure and its construction parts take the centre stage. Technically, it is part of dimensioning, but should be considered, if possible, to achieve a higher degree of protection with a little more effort (e.g. adding a climate-factor of 15% for the hydraulic dimensioning of new constructions).

"HOW-to” manage a torrential protection system in a holistic Way

'IWEK' - a top-down-Approach

Torrent control in Bavaria has a long history. An inventory has shown that today there exist about 50.000 protective buildings in mountain streams, whereby many of them are in need of rehabilitation. For the critical investigation to find out if old protection measures correspond to present conditions in torrent-catchments and for the adaption to future developments (e.g. case-of-overload), "Integrated torrential development concepts" (IWEK) will prospectively be developed for relevant torrents in Bavaria. Within these concepts, the treatment of the protection system is divided into four different levels of consideration: protection system (1), function groups (2), structural measure (3) and construction parts (4).

In the first level, the current protection system has to be analysed and assessed in a holistic way concerning past and future developments. It is necessary to figure out what the initial purpose of the constructions was, whether their function is still needful or not and if they can withstand future events. In addition, the present and future boundary conditions for the further planning have to be defined.

In the second level, the key-processes, -functions and -activities have to be identified and combined to functional sections. For these sections different measures (technical/bioengineering/organisational) have to be detected. All measures with the same function in one section form a function group. To cope with the case-of-overload it is necessary to take interactions between all measures into account.

The third level has the focus on the structural measure. Based on the preliminary works the current state and the initial function of the construction and the functions to be fulfilled are given. For the handling of constructions, the following options are possible: adoption, rehabilitation, optimisation, new construction/replacement measure, deterioration/renaturation.

In the fourth level, the design of a single structural measure and its construction parts take the centre stage. Technically, it is part of dimensioning, but should be considered, if possible, to achieve a higher degree of protection with a little more effort (e.g. adding a climate-factor of 15% for the hydraulic dimensioning of new constructions).

In order to test the practicability of the top-down-approach described above and to find difficulties and solutions, four different engineering offices have the job to apply it to different torrential catchments in Bavaria. The adaption for each catchment will be finished in summer 2019. The final outcomes will also be presented.

Processes like fluvial flows (floods with or without intensive bedload transport) or debris flows represent extreme events in torrential catchments that can transfer large amounts of sediment to the receiving river or alluvial fan. In contrast to fluvial flows, the formation of debris flows is the result of a critical combination of water, sufficient sediment that can be mobilized, and topographic slope. In alpine regions, excessive water input typically results from long lasting rainfall (LLR), short duration storms (SDS) or intense snow melt (SM). In a recent study, we derived multiple hydro-meteorological variables from long-term hydrological simulations to investigate the trigger conditions of fluvial flows and debris flows in six regions in Austria. We found distinct regional and seasonal differences, but overall roughly 2/3 of the debris flows were initiated by SDS events and 1/4 by LLR events, the remaining by SM. Fluvial flows tend to results from a higher total precipitation input than debris flows. When ex-post predicting the susceptibility for debris flow initiation with a Naïve Bayes Classifier model, we found that multi-variable trigger models outperformed simple intensity-duration thresholds. The remaining uncertainty we largely attribute to the unknown sediment dynamics in the watersheds that were not included in the susceptibility assessment. We conclude that the consideration of different hydro-meteorological trigger types improves engineering risk assessment.

Prediction of a watersheds temporal susceptibility to debris flows using multiple hydro-meteorological variables

Prenner D., Kaitna R., Mostbauer K., Hrachowitz M.

Debris flows represent a threat for societies in alpine regions and are typically triggered by excessive water input from long lasting rainfall (LLR), short duration storms (SDS) or intense snow melt (SM) into torrential watersheds. The prediction of debris flow events mostly relies on rainfall intensity and duration (I-D) alone, which is often less reliable for practical applications because of the high spatial variability of precipitation. To overcome this limitation, we utilize multiple hydro-meteorological variables like snow melt, evapotranspiration, soil moisture from a hydrological simulation besides station data of precipitation and temperature to predict the temporal susceptibility of the Montafon watershed to debris flows between 1953 and 2013. Therefore, we setup four Naive Bayes Classifier models of different complexity, ranging from simple rainfall only to multi-variable, multi-trigger type as well as a classical I-D curve and evaluate the performance using Receiver Operating Statistics. Results show that the watershed is in very different states in dependence of the trigger of either LLR, SDS or SM on the 38 documented debris flow event days in the region. The multi trigger-type models outperform the simpler models as well as I-D curve by showing both, higher true positive rates and lower false alarm rates. We conclude that, the consideration of hydro-meteorological variables can help to improve debris flow prediction in future.

As a common measure to stabilize the torrential channel bed and to prevent erosion, a series of check dams offers a dosing function to bed load transport. By providing river sections with decreased slopes, it reduces sediment transport at high bed load rates and offers the possibility to remobilize these sediments during lower flow rates by changing the compensation angle. In this case, slope of deposition is mainly a function of the volumetric sediment concentration and the mean grain diameter. The temporary changing effects of intermittent deposition and erosion are on the one hand sufficiently protecting mountain regions from sediment overload capacities and on the other hand sustaining the sediment connectivity. To quantify resp. to give a rough estimation of the possible temporary deposition, laboratory experiments and investigations were carried out. As a result, a simple calculation method was developed to determine the maximum and minimum temporary sediment storage volume and the angle of deposition under different natural conditions, including channel geometry sediment composition, discharge and volumetric sediment concentration. In a further step, these results provide the basis for the optimization and dimensioning of the structural parameters of a series of check dams. The developed method provides the possibility to define the sedimentation freeboard at the check dam, the constructive height of the individual structures, the varying distances between check dams and therefore the necessary number of check dams of a particular torrent. To sum up, a series of check dams is regulating sediment rates by offering natural balancing processes. Through targeted optimization of the distances and heights of the dams, these dosing effects can be artificially directed and used in cases of sediment management and torrential flood protection.

Alpine regions are exposed to different mass wasting processes, including debris flows, landslides, and rock fall. Debris flows are highly mobile gravity driven mixtures of sediment and water, that can exhibit different flow states, and can alter the flow behavior during a single event. The combination of high velocities and the capacity to carry large boulders endangers human lives and infrastructures. Small-scale models are often limited to reproduce the complex dynamics. For the design of mitigation measures and for back-calculations, realistic values of the range of impact pressures are required, but rarely available. In this contribution, we present first results of in-situ measurements of the natural debris-flow impact pressures onto a debris flow breaker at the Gadria torrent, Italy. The measured forces support the notion to differentiate between dynamic bulk impact and impacts by single boulders. The data also highlight the problem at low Froude numbers to define the empirical coefficient in the hydrodynamic models currently used. Our study contributes to data densification of real-scale debris flow impact forces and aims for a better understanding of the complexity of the interactions between the flow process and engineering structures.

 Understanding the impact dynamics on buildings caused by fluviatile sediment transport processes is a major challenge. Floods with large amounts of mobilized sediments can cause severe damages to exposed building structures located within flood-prone torrential fans. Mitigation efforts either rooted in spatial planning or in local structural protection may benefit from better insights into impact dynamics. To gain a better understanding of the interaction between torrential processes and buildings and thereby to measure impact forces on buildings and to comprehensively assess determining factors, physical scale models can be applied. In this context, the present workshop contribution discusses results of a physics-based case study analysis of the torrential fan of the Schnannerbach Torrent (Eastern European Alps, Austria). The model covers the steep torrent channel and the adjacent floodplain, hosting complex building structures equipped with measurement devices on the wall elements to measure the three-dimensional impact forces of the torrential process. The experiments show that the impact forces depend mainly on the dynamics of the sediment deposition processes on the floodplain that are also influenced by the spatial distribution of the building structures, and less on the intensities of the analysed flood events and the sediments characteristics. The results highlight the need to consider the interaction between the natural process and the built environment as well as the spatial distribution of buildings and their mutual interaction (shadowing vs. channelization) in flood risk management.

Fold-and-thrust belts form in the external parts of orogenic belts due to compression. The NCA are a fold-and-thrust belt active from the Cretaceous to the present day. The ongoing N-S shortening between the Adriatic and the European plates causes seismic events and is responsible for the inversion of rift-related half grabens in the lower, European plate. Currently, the intensity of earthquakes in the NCA is low (M_L ≥ 2-3; Reiter, F. 2018) and hypocenters are not accessible. However, the NCA are an excellent place to study today’s inactive thrust planes on exposed structures to understand thrust tectonics and to draw conclusions for deep structures in fold and thrust belts.

Two cross sections from the Karwendel and the Mieminger chain were selected to study the different behaviour of thrust sheets (Kilian, Ortner, 2019; Ortner, Bitterlich, 2016). These two examples could be end members of a deforming multilayer complex. In the Karwendel mountains the thrust behaves according to existing models for hanging wall flat geometries: the thrust runs more or less parallel to bedding along a decollement. In contrast, in the Mieming chain buckle folding is older than thrust sheet transport; buckle folds develop into break-thrust folds, and then the thrust cuts across the fold train in its foreland.

Numerical investigations are carried out to estimate the influence of the material properties (e.g., stiffness, strength, layering) on the development of thrust belts built by buckle folds. We target to develop new rules for the construction of cross sections and improve geologic models, which are a prerequisite for the assessment of earthquake hazards in compressive settings. As the intensity of ground shaking depends on the depth of the event (Somerville & Pitarka, 2006), a rheologic-geometric model would upgrade risk management (e.g., earthquakes as trigger for slope movements) in fold and thrust belts.

Building a thrust belt using buckle folds -

a numeric approach in the Northern Calcareous Alps

Shallow landslides differentiate themselves from debris flows as a spontaneous and very rapid process (up to 15 m/s), relatively small volume of material (20-200 m³), originating from a supersaturated slope made of vegetation cover and loose material on top of bedrock. When the material is guided towards a channel, a much larger debris flow can develop (Wendeler et al., 2016). This site was identified by a report of Winter et al., 2005, being one at the highest risk of landslides and debris flows in the UK. The geology is characterised by peat, topsoil and colluvium on top of schist bedrock (British Geological Survey). The road being an important connection, with closures forcing a detour of 55 miles, flexible protection measures were installed in 2010. A notable landslide occurred during storm Desmond in Winter 2015. The shallow landslide barrier caught successfully approx. 100 tonnes. Three years later, the next storm brought heavy rain and the slope failed numerous times, across several channels. Approx. 3000 tonnes of material closed the road for 4 weeks (Bearscot website), while repeated landslides occurred. Large boulders within the colluvium layer were exposed and posed a rockfall threat. The shallow landslide barrier worked well for the first impact but was not designed for the following impacts (Wendeler, 2010). A second surge overflowed the barrier damaging the upper rope, either by a rock impact or load excess from overflow. The EAD for CE marking of flexible shallow landslide kits states that overflow is an additional considerable load case. Higher loads acting on the upper ropes leads to doubling and or strengthening the support ropes and adding abrasion protection to the design of the system. If overflow is a possible design case for shallow landslide barriers, important adaptation to the flexible system are necessary.

During the past century, many European mountain areas experienced strong land cover changes controlled by land abandonment patterns, which resulted in an increase in forest cover at the expense of pasture lands. Such changes in land cover can potentially affect avalanche activity,causing changes in risk for the locals potentially enhanced by concomitant changes in population, urban areas and critical infrastructures. Here, a refined diachronic analysis of historical maps and aerial photographs track the evolution of land cover in the upper Maurienne massif,French Alps, over the past 160 years, with special focus on avalanche prone terrain. Results confirm a continuous increase in forested areas associated with the retraction of agro-pastoral zones in the entire upper Maurienne since 1860. Avalanche prone areas mimic overall the same evolution pattern. However, a more detailed photographic interpretation of the evolution since the mid-twentieth century demonstrates that reforestation within avalanche paths remains largely incomplete and mostly absent in the majority of release zones. This makes a decrease in avalanche release and propagation potential due to afforestation largely questionable in the studied area. Moreover, since 1950, the area witnessed a rapid urban sprawl driven by a surge in tourism. Part of this expansion occurred in the vicinity of avalanche paths, locally increasing the vulnerability of urban areas to avalanches. Hence, overall, avalanche risk for buildings and inhabitants has probably not decreased, and it may even have increased locally, explaining why construction of huge mitigation structures has been found unavoidable by local authorities. Nonetheless, changes in snow amounts and other weather variables controlling avalanche activity in the current context of accelerated warming could temper this conclusion. Therefore, the combined impact of climate and land cover changes on avalanche activity should be considered in further work to ascertain our evaluation of avalanche risk evolution in the upper Maurienne valley.

The rapid glacier recession in the European Alps exposes high amounts of unconsolidated sediment, especially in the form of moraines. Several processes are involved in the reworking of this sediment on steep lateral moraines, e.g. small slides on the steep upper slopes, sheet erosion by snow gliding and debris flows. The temporal development of the morphodynamics after deglaciation depends on the abundance of loose sediment, the presence of dead ice in the slope, the slope gradient, moisture availability and the altitude a.s.l. of the respective slope, amongst others.

To gain deeper insight into the dependence of the morphodynamics on lateral moraines on the time since deglaciation, we analyse erosion rates and geomorphological processes occurring on small test areas situated at different distances from the present-day glacier termini. Moreover, we assess the significance of parameters like initial slope gradient, moisture availability and the presence of dead ice for the morphodynamics and examine whether their impact can surpass and thereby obscure the influences of the distance from the glacier tongue and the altitude a.s.l.

For our analyses, several moraine tracts of 10 glaciers in the German, Austrian, and Italian Alps are investigated. The glacier forefields not only differ in their location within the Alps, but also regarding their altitude a.s.l. and size.

For the long-term detection of sediment reworking, we use a series of historical aerial images to generate Digital Elevation Models (DEM) by photogrammetric analyses. In order to detect recent geomorphological processes in detail, we derive highly accurate DEMs from our own UAV-surveys conducted in summer 2017 and 2018.

Debris flows are dangerous natural hazards that every year cause fatalities and damages to infrastructures. One of the challenges of the last decades is to predict the dynamics of such events using specific numerical models. The aim of this study is to satisfactorily reproduce the progressive erosion dynamic of a debris flow starting from a channelized water flux. This kind of process was reproduced exploiting the functionality of the r.avaflow model that is capable to simulate a two-phase mixture of gravity mass flows.

The investigated study case occurred near the village of Cortina D’Ampezzo (Veneto Region, Italy) during the 2017 summer. The debris flow was triggered by an extreme rainfall event that caused an intense runoff, entraining sediment materials from the channel bed and then generating a mature granular debris flow. To reproduce the erosion pattern, the modelling approach developed in r.avaflow was improved. Specifically, the input erosion coefficient was varied according to a calibrated exponential function of the local slope. Another simulation was performed using the best constant erosion coefficient to assess the performance of the improved model.

The results of these two simulations were then compared with the observed (LiDAR surveys) erosion pattern. In particular, using a slope dependent erosion coefficient, the entrained volumes and the erosion trend resulted in a more reliable topography than those produced by a constant erosion coefficient. The same good performance was obtained in terms of bulked peak discharge flowing 1.4 km downstream of the input water hydrograph.

In conclusion, the research has highlighted the satisfactorily simulation of debris flow triggering for r.avaflow model and provided a supplementary methodology of model implementation for a more accurate prediction of debris flow erosion.

Understanding morphology changes and sediment spreading along a debris-flow channel is a key step in hazard mitigation planning. 

This research analyses a 10 years evolution of erosion/deposition patterns in an active debris-flow upper channel located on the Dolomites (rio Soial, Val di Fassa, Trento, Italy). The morphologic evolution of the channel has been analysed performing a Difference of DEM (DoD) and comparing the 2008 LiDAR-derived DTM of the Autonomous Province of Trento with a DTM created from a UAV-based point cloud of the July 2018. This data set was also used to determine the changes of the sediment Connectivity Index (CI), which explains the existing degree of linkage between sediment sources and channel network. During the period 2008-2018 five debris flow events have occurred. Each associated rainstorm was analysed in order to assess the evolution of the threshold rain intensities for the triggering in relation to the evolution of the channel-valley morphology. 
The results on the CI analysis show a general decrease in CI values, meaning an increased disconnection between the head basin areas and the outlet at the end of the transport reach. Also, the rain thresholds show a slight increase after the lasts event, indicating a gradual stabilization of the basin and a possible reduction of the expected frequency of debris flow events.

Since the beginning of the 20^th century, temperatures in Alps have increased of about 1.5°C but the impacts of global warming on mass movements remain poorly studied. In the specific case of rockfall, a few studies have documented an increase in high-altitude rockfall frequency related to global warming and permafrost degradation. Paradoxically, the impacts of climatic change on rockfall activity only poorly discussed so far at lower altitude where the stakes are concentrated.

On forested slopes, dendrogeomorphic techniques - that provide absolute numbers of past rockfalls and their spatial distribution - represent a reliable alternative to overcome these knowledge gaps.

Our analysis was conducted in a forested plot of the Saint-Guillaume municipality in Vercors Massif, affected by rockfall hazards within a mixed forest stand. In total, 601 rockfalls related growth disturbances (GD) were dated in the tree rings series of 179 trees. The resulting rockfall reconstruction covers the period 1838-2018. It shows a clear increase from 0.012 event.decade.tree^-1for the period 1961-1970 to 0.081 event.decade.tree^-1 between 2001 and 2010 obviously related to the difficulty to determine suitable coring positions for old masked scars. Some years like 2010 (26 GD) or 2002 (24 GD) can be identified as years of very active rockfalls.

For the recent period (1918-2017), our reconstruction was correlated with monthly meteorological series (temperatures and precipitations) from the Monestier station (3km of study site) to see the influence of meteorological fluctuations on rockfall activity.

No meteorological parameter is significantly correlated with our reconstruction thus highlighting the complexity to explain the trend towards increased rockfall activity. In the future, daily meteorological data and additional covariables (freeze-thaw cycles) will be tested to identify potential triggering factors. Also, analyses of the long range trend will be undertaken to distinguish – if possible – the forest stand effect from climate and land-use change impacts.

Forecasting glide-snow avalanches is currently one of the trickiest issues for operational avalanche warning services, local avalanche commissions, as well as for avalanche research. While the prerequisite for glide-snow avalanches, namely a moist interface between the snow-cover and the ground, is well known, estimating the timing for glide-snow avalanche release, which can range between immediately to weeks after the opening of a glide-crack, remains a challenge. Within this study glide-snow avalanche activity recorded for five winter seasons (2009/10 – 2010/11 and 2015/16 – 2017/18) were compared to measured meteorological parameters for the specific test site Planneralm in Styria, Austria. Univariate and multivariate statistical analyses were used to identify the most significant meteorological parameters: snow height, five-day sum of snow accumulation, mean air temperature, and maximum snow surface temperature. A random forest model approach was tested for its applicability in differentiating between avalanche and non-avalanche days. The model used the meteorological parameters as predictors, and the avalanche observations from an automated camera served as reference. Our results showed a high predictive power and model accuracy where a central finding was the necessity of hourly data resolution for a correct prediction of avalanche- and non-avalanche days. Generally, the model results showed high conformity with the findings of other studies and eventually could be implemented as a supporting tool for avalanche forecasting services. Nevertheless, further research with extended data as well as application on other regions is recommended in order to evaluate the model results.