Christian Conoscenti

Gully erosion susceptibility assessment by means of GIS-based logistic regression: A case of Sicily (Italy)

article i nfo Article history: This research aims at characterizing susceptibility conditions to gully erosion by means of GIS and multivariate statistical analysis. The study area is a 9.5 km 2 river catchment in central-northern Sicily, where agriculture ac- tivities are limited by intense erosion. By means of field surveys and interpretation of aerial images, we prepared a digitalmap of thespatial distribution of 260 gulliesinthestudy area.Inaddition,fromavailable thematicmaps, a 5 m cell size digital elevation model and field checks, we derived 27 environmental attributes that describe the variability of lithology, land use, topography and road position. These attributes were selected for their potential influence on erosion processes, while the dependent variable was given by presence or absence of gullies within two different types of mapping units: 5 m grid cells and slope units (average size = 2.66 ha). The functional re- lationships between gully occurrence and the controlling factors were obtained from forward stepwise logistic regression to calculate the probability to host a gully for each mapping unit. In order to train and test the predictive models, three calibration and three validation subsets, of both grid cells and slope units, were randomly selected. Results of validation, based on ROC (receiving operating characteristic) curves, attest for acceptable to excellent accuracies of the models, showing better predictive skill and more stable performance of the susceptibility model based on grid cells.

Binary logistic regression versus stochastic gradient boosted decision trees in assessing landslide susceptibility for multiple-occurring landslide events: application to the 2009 storm event in Messina (Sicily, southern Italy)

Abstract This study aims to compare binary logistic regression (BLR) and stochastic gradient treeboost (SGT) methods in assessing landslide susceptibility within the Mediterranean region for multiple-occurrence regional landslide events. A test area was selected in the north-eastern sector of Sicily (southern Italy) where thousands of debris flows and debris avalanches triggered on the first October 2009 due to an extreme storm. Exploiting the same set of predictors and the 2009 event landslide archive, BLR- and SGT-based susceptibility models have been obtained for the two catchments separately, adopting a random partition (RP) technique for validation. In addition, the models trained in one catchment have been tested in predicting the landslide distribution in the second, adopting a spatial partition (SP)-based validation. The models produced high predictive performances with a general consistency between BLR and SGT in the susceptibility maps, predictor importance and role. In particular, SGT models reached a higher prediction performance with respect to BLR models for RP-modelling, while for the SP-based models, the difference in predictive skills dropped, converging to equally excellent performances. However, analysing the precision of the probability estimates, BLR produced more robust models around the mean value for each pixel, indicating possible overfitting effects, which affect decision trees to a greater extent. The assessment of the predictor roles allowed identifying the activation mechanisms which are primarily controlled by steep south-facing open slopes located near the coastal area. These slopes are characterised by low/middle altitude downhill from mountain tops, having a medium-grade metamorphic bedrock, under grassland and cultivated (terraced) uses.

Multi-method Evaluation of Denudation Rates in Small Mediterranean Catchments

The paper presents the results of the research tasks of the Quantitative Geomorphology Working Group (of the Italian Association of Physical Geography and Geomorphology) focused on multi-method evaluation of denudation rates in small catchments of Italy. Several study areas are compared with the goal of quantifying the morphodynamic evolution in different response times and with traditional and innovative techniques. The final aims are the direct erosion monitoring, the geomorphic analysis for the comprehension of drainage basin morphodynamics, up to the geomorphological hazard evaluation. The catchments are key Mediterranean areas particularly sensitive to climatic and anthropic modifications. The efforts of the Working Group are finalized to favour scientific collaboration activities among members with the aim of strengthen the potential of Quantitative Gomorphology in morphodynamic studies.

Landslide susceptibility mapping using precipitation data, Mazandaran Province, north of Iran

Precipitation is a nonlinear and complex phenomenon and varies in time and space. It is also evident that there is a link between precipitation and shallow landslides, and precipitation is always considered as a landslide-triggering factor. This study aims to investigate the relationship between the characteristics of precipitation and the historical shallow landslides in Mazandaran Province, north of Iran. For this purpose, the spatial variability of rainfall was analyzed using monthly rainfall data collected at 15 synoptic stations distributed over the region between 1981 and 2014. Monthly precipitation and other derived parameters were used, and a hybrid model combining principal component analysis and cluster analysis (CA) was applied to all the precipitation parameters to regionalize the region into well-defined clusters in terms of precipitation and prove that there is a link between precipitation and the occurred slides. Then, the rotated PCs were combined and the precipitation characteristics map was produced. Demonstrating the linkage between the precipitation characteristics and the historical slides, the combined map can be considered as landslide susceptibility map. The accuracy of prediction was tested against a random guess and obtained as 77%. It is also noticeable that only 30% of the surface area of the study region in the landslide susceptibility map covers about 80% of the known landslides. The calculated measure suggests that the developed model well predicted the location of the occurred slides using only precipitation data.

Geomorphology of the Capo San Vito Peninsula (NW Sicily): An Example of Tectonically and Climatically Controlled Landscape

The Capo San Vito peninsula is located along the north-westernmost sector of the Sicilian coastline. It is characterized by a complex geomorphological setting, where a large variety of coastal, gravity-induced and karst landforms allow the visitor to easily detect the interactions between Quaternary tectonics and climate changes as well as morphodynamic processes responsible for shaping the landscape. Thanks to natural reserves, the peninsula preserves a typical Mediterranean natural environment, marked by spectacular and suggestive landforms.

Pantelleria Island (Strait of Sicily): Volcanic History and Geomorphological Landscape

Pantelleria is a volcanic island located in the Strait of Sicily, 95 km far from the Sicilian coastline and 67 km from Cape Bon (Tunisia). The volcanological history of the island begins approximately 324 ka BP and the last eruptive event was a submarine eruption that occurred on 1891 A.D. Eruptive activity was characterized by seven very intense explosive events, the latest being the Green Tuff (44 ka). They have all produced ignimbrite sheets that covered large sectors of the island. The landscape of the island mirrors the variety of the eruptive styles and their interplay with volcano-tectonics. The most evident geomorphological features are represented by: (i) the mantle-like distribution of the Green Tuff ignimbrite; (ii) the arcuate remnants of the two large caldera collapses, and (iii) the intracalderic scoria cones, lava domes and lava fields. A very dense distribution of dry walls, built since Roman times, perfectly integrate the volcanic landscape, preventing from erosion and rock falls.

GPS Monitoring of the Scopello (Sicily, Italy) DGSD Phenomenon: Relationships Between Surficial and Deep-Seated Morphodynamics

The Scopello area, which is located along the north-western Tyrrhenian coastal sector of the Sicilian chain (Italy), is widely affected by Deep-seated Gravitational Slope Deformation (DGSD) phenomena, which are mainly the result of a geomorphologic setting marked by the outcropping of an overthrust plan, limiting a brittle fractured carbonate slab, laid onto a ductile marly-clayey substratum. Due to the very advanced stage of the deformation phenomena, a coupled morphodynamic style has established between shallow landslides and DGSD phenomena, affecting the exhumed ductile substratum and the overlaying rigid dismantled slab, respectively. A GPS network was realized for monitoring the Scopello landslide, consisting of 27 vertexes, which were directly cemented either onto rock or debris blocks or concrete structures rooted on the marly–clayey substratum. The geometry of the network and the geodetic technique adopted for the GPS signal acquisition allow the survey for a sub-centimetric precision in the positioning of the vertexes. On February 2005 earth-flows and block/slab-slides movements affected the head sector of the landslide area. The displacements field, which was derived by comparing the results of a pre- (2004) and a post-event (2005) GPS surveys, is here analyzed and discussed. On the basis of the observed displacement, the connection between surficial and deeper ground deformations is confirmed.