F. Cazorzi

Snowmelt modelling by combining air temperature and a distributed radiation index

High spatial variability in snowmelt phenomena was observed in the experimental watershed of the upper Cordevole (7 km2), in the Dolomites. Snowmelt depends, at a point scale, on available energy, which in turn is heavily affected by slope, aspect and shading effects of the site. A distributed hourly model of snowmelt was set up as a geographical information system (GIS) module. The model accumulates snowfall for each raster element (20 m × 20 m) using a temperature threshold. It simulates snowmelt using air temperature and a radiation index consisting of daily average values of clear sky radiation that have cumulated at selected dates since 21 December. It should be underlined that the only relevant calibration parameter of the model is the combined snowmelt factor, which is unique for the whole basin. The clear sky radiation maps were computed for a selected period of the year, based on the watershed digital terrain model and the solar path sampled at very short intervals. When run for a season, the model produces snow water equivalent maps at given dates. The model was validated, with satisfactory results, by comparing these maps with 60 snow covered area surveys and related water equivalent measures collected in six snowmelt seasons from 1986 to 1991. The classical temperature index approach to snowmelt modelling does not allow the full variability over the basin to be taken into account. Besides, it seems important to point out that this fully distributed approach allows us to avoid the use of snow covered area (SCA) depletion curves, the definition of which still proves a troublesome task.

Recognition of surface flow processes influenced by roads and trails in mountain areas using high-resolution topography

Abstract Road networks in mountainous forest landscapes have the potential to increase the susceptibility to erosion and shallow landsliding. The same issue is observed also for minor trail networks, with evidences of surface erosion due to surface flow redistribution. This could be a problem in regions such as the Italian Alps where forestry and tourist activities are a relevant part of the local economy. This is just one among the several effects of modern anthropogenic forcing: it is now well accepted by the scientific community that we are living in a new era where human activities may leave a significant signature on the Earth, by altering its morphology, and significantly affecting the related surface processes. In this work, we proposed a methodology for the automatic recognition of roads and trails induced flow direction changes. The algorithm is based on the calculation of the drainage area variation in the presence, or in the absence of anthropic features such as roads and trails on hillslopes. To simulate the absence of alteration, the surface was smoothed considering moving windows of varying size. In the analysis, we used a 1 and 0.5 m Airborne Laser Swath Mapping technology (ALSM), using LiDAR (Light Detection And Ranging), and 0.2 m Terrestrial Laser Scanner (TLS) derived Digital Terrain Models (DTMs). The aim of the work is to underline the effectiveness of the proposed method based on high resolution topography in the detailed recognition of surface flow direction alteration due to roads, but also trail networks. We propose an automatic method to map at a large scale such alterations, also in areas where it is difficult to recognize them without a trail network surveyed in the field. This methodology could be considered as a support for modeling (i.e., terrain stability and erosion models), and it can be used to interactively assist the design of new infrastructure to reduce their effects on surface instabilities. The reported methodology could also have a role in risk management and environmental planning for mountain areas where tourism and the related economic activities are critical, and where also trails deserve attention due to induced slope instabilities.

Current Behaviour and Dynamics of the Lowermost Italian Glacier (Montasio Occidentale, Julian Alps)

Abstract Smaller glaciers (<0.5 km2) react quickly to environmental changes and typically show a large scatter in their individual response. Accounting for these ice bodies is essential for assessing regional glacier change, given their high number and contribution to the total loss of glacier area in mountain regions. However, studying small glaciers using traditional techniques may be difficult or not feasible, and assessing their current activity and dynamics may be problematic. In this paper, we present an integrated approach for characterizing the current behaviour of a small, avalanche‐fed glacier at low altitude in the talian lps, combining geomorphological, geophysical and high‐resolution geodetic surveying with a terrestrial laser scanner. The glacier is still active and shows a detectable mass transfer from the accumulation area to the lower ablation area, which is covered by a thick debris mantle. The glacier owes its existence to the local topo‐climatic conditions, ensured by high rock walls which enhance accumulation by delivering avalanche snow and reduce ablation by providing topographic shading and regulating the debris budget of the glacier catchment. In the last several years the glacier has displayed peculiar behaviour compared with most glaciers of the uropean lps, being close to equilibrium conditions in spite of warm ablation seasons. Proportionally small relative changes have also occurred since the Little Ice Age maximum. Compared with the majority of other Alpine glaciers, we infer for this glacier a lower sensitivity to air temperature and a higher sensitivity to precipitation, associated with important feedback from increasing debris cover during unfavourable periods.

Reconstructing Fluctuations of La Mare Glacier (Eastern Italian Alps) in the Late Holocene: New Evidence for a Little Ice Age Maximum Around 1600 AD

Abstract Field observations, old terrestrial photographs and maps, aerial orthophotos and detailed geomorphological mapping were used for compiling and validating a 119‐year cumulative record of terminus changes for a are lacier, astern talian lps. ate olocene glacier maxima preceding direct observations were reconstructed by applying age dating techniques (radiocarbon and lichenometry) to glacial deposits in the proglacial area of the glacier. Results show that the glacier reached its maximal position around 1600 ad, followed by smaller advances in the eighteenth century, while in the nineteenth century it did not reach or overrun these positions. A similar behaviour for neighbouring glaciers was reported by previous works, documenting absolute ate olocene maxima in the seventeenth or eighteenth centuries. By contrast, multi‐century reconstructions available for the north‐western lps show that in the nineteenth century, glaciers were at their maximum or very close to previous maxima achieved in the first half of the seventeenth century. Climatic causes for these discrepancies have been examined, analyzing multi‐proxy climatic reconstructions starting in 1500 ad, but also morphodynamic processes linked to the bedrock characteristics of a are lacier could have played a role in modulating its response to climatic changes.

Enhanced estimation of glacier mass balance in unsampled areas by means of topographic data

Abstract A new method was developed to estimate the mass balance in unsampled areas from existing datasets. Three years of mass-balance data from two glaciers in the central Italian Alps were used to develop and test a multiple-regression method based exclusively on a 10m resolution digital terrain model. The introduction of a relative elevation attribute, which expresses the degree of wind exposure of the gridcells, notably increased the amount of explainable variance in winter balance with respect to altitude itself. The summer balance is highly correlated with elevation, but, in order to obtain reliable extrapolations, the clear-sky shortwave radiation and the diurnal cloud-cover cycle had to be taken into account. The net annual mass balance on a glacier system comprising the two monitored glaciers was calculated by applying both a single regression of winter and summer balance with altitude and the new regression method. The consistency of results was assessed against measured net balances and snow-cover maps drawn in the ablation season. The results of the new method were in close agreement with observations and proved to be less sensitive to the spatial representation of the sampled areas.

Debris-Flow Monitoring and Geomorphic Change Detection Combining Laser Scanning and Fast Photogrammetric Surveys in the Moscardo Catchment (Eastern Italian Alps)

Monitoring debris-flow prone catchments and collecting field data is of extreme importance for improving the knowledge and therefore the management of such hazardous phenomena. High-resolution Digital Elevation Models (DEMs) have recently established as an important tool for the study of geo-hydrological and geomorphological processes. Monitoring surface changes over time allows to analyze sediment dynamics from several points of view, ranging from the accounting of volumetric changes to numerical modeling, to the correlation of morphometric indexes with different components of geo-hydrological processes. The present study examines the Moscardo Torrent, a small alpine stream in the Eastern Italian Alps which is characterized by a high occurrence of debris flows. The original monitoring instrumentation, which made it possible to record hydrographs of 15 debris-flow events in the years 1989–1998, was renewed, allowing to record three debris flows in the years 2011–2012. Surface morphology of three areas exposed to debris-flow dynamics was surveyed across the recorded debris-flow events by means of Terrestrial Laser Scanning (TLS), and 0.2 m DEMs of Differences (DoDs) were calculated. During the third TLS campaign, close-range digital photogrammetric images were acquired in order to directly compare 3D surface representation with the high-resolution DEMs derived by TLS.

Development and application of a real-time flood forecasting system in the Veneto region of Italy

The paper describes three flood forecasting models used in the framework of the integrated hydrological forecasting system of the Veneto Region. The three models are based on the unit hydrograph theory, even though the computation of the “effective” rainfall and the real-time correction procedure are carried out in different ways. A comparison of the model performances is also made.

Monitoring topographic changes through 4D-structure-from-motion photogrammetry: application to a debris-flow channel

The study of fast geomorphic changes in mountain channels and hillslopes, driven by intense geomorphic processes, requires frequent and detailed topographic surveys. In the last two decades, high-resolution topography (HRT) has provided new opportunities in the Earth Sciences. These have benefited from important developments in surveying techniques, methods, sensors, and platforms. Between these, the application of structure-from-motion (SfM) photogrammetry has become a widely used method to acquire HRT and high-resolution orthomosaics at multiple temporal and spatial scales. SfM photogrammetry has revolutionized the possibility to collect multi-temporal HRT in rugged or inaccessible environments like that observed in debris-flow catchments. However, appropriate workflows incorporating survey planning, data acquisition, post-processing, and error and uncertainty assessment are required, especially when multi-temporal surveys are compared to study topographic changes through time. In this paper, we present a workflow to acquire and process HRT. The workflow was applied in a debris-flow channel of the Moscardo Torrent (Eastern Italian Alps). Due to the topographic complexity of the study area, the SfM surveys were carried out integrating photos obtained from an unmanned aerial vehicle and from the ground. This integration guarantees high data density and avoids shadows. Eight photogrammetric surveys were collected between December 2015 and August 2017. In this time interval, five debris flows occurred. The surveying and data processing procedure described in the workflow permitted to summarize and integrate all the analysis steps and helped to identify and minimize potential sources of error in the multi-temporal SfM data (what we consider here 4D). Our case study demonstrates how the developed workflow presented here allows studying the geomorphic effects of debris flows and check dams functionality in mountain environments.