Urban geomorphology of a historical city straddling the Tanaro River (Alessandria, NW Italy)

The integration of \ufb01eld surveys, bibliographic research and multitemporal analysis of historical maps, aerial photographs and satellite images in a GIS environment, allowed the current and past geomorphological features of the old city of Alessandria and its surrounding areas, NW Italy, to be identi\ufb01ed and mapped. Their analysis provided an overview of the geomorphological evolution of the city that is strictly related to the historical vicissitudes occurred since the Middle Ages. Nowadays, the most representative landforms and deposits characterizing the urban landscape result from human interventions and are associated with ancient military facilities and infrastructures, a historical man-made channel network no longer recognizable, the Tanaro riverbed channelization, and the urban sprawl occurred from the second half of the nineteenth century onwards. This study represents a useful tool for urban planning and management and for raising the citizens\u2019 awareness of the urbanlandscape geomorphological features and evolution, and therefore the geo-hydrological risk

Translational Rock-Block Slides in a Tertiary Flyschoid Complexes of Southern Piedmont Region (North-West Italy)

The southern Piedmont Region (north-west Italy) is characterized by a hilly zone called “Langhe” that covers an area of about 2300 km2 and is bordered by Tanaro River at north and west, by Orba River at east, and by Apennine mountains at south. The Langhe is rolling hills famous for their excellent wine, populated by many small inhabited centers since ancient times. An idea of the Langhe geomorphology can be gained by studying the word “Langa”: it may have been derived from either “landa,” which means a wild and uninhabited place or from “lingua,” which means a strip of land. The morphology of the Langhe hills is characterized by asymmetrical valleys with steep south-east facing slopes and more gentle north-west facing slopes: their profile is defined “saw toothed” by local inhabitants. The asymmetric shape is clearly conditioned by the geology. Severe hydrological events occurred in the last 100 years in Piedmont in particular on May 1926, February and March 1972, February 1974, and November 1994. During these long rainy periods, on the gentler slopes, translational rock-block slides involve tertiary flyschoid complexes represented by rhythmic series of deposits with varied grain size. These landslides often damage or destroy buildings and roads, even if rarely claim human lives

Exposure\ua0to\ua0Geo\u2010Hydrological\ua0Hazards\ua0of\ua0the\ua0 Metropolitan\ua0Area\ua0of\ua0Genoa,\ua0Italy:\ua0A\ua0Multi\u2010Temporal\ua0 Analysis\ua0of\ua0the\ua0Bisagno\ua0Stream\ua0

Geo\u2010hydrological  risk  reduction  policies  are  becoming  a  critical  challenge  for  environmental sustainability, both at the national and international levels. The reason is twofold:  On the one hand, climate change has increase rainfall frequency and intensity, while on the other,  reckless urban expansion has increased exposure to such hazards over time. Italy is a country that  is very vulnerable to flood and landslide hazard; the city of Genoa, which, in recent decades, has  been frequently hit by severe floods, has risen to symbolize Italian geo\u2010hydrological risk. Recent  studies  on  Genoa\u2019s  geo\u2010hydrological  hazard  have  focused  on  the  analysis  of  hydrogeomorphological features of the Bisagno stream basin, yet their main focus was on hazard control.  Very little research has been done to enhance the understanding of the source of risk in such  catchments. This paper presents a study on the increased urban exposure and vulnerability to geohydrological hazard along the Bisagno stream catchment area over the last 200 years. Morphometric  analyses were coupled with historical documents showing the evolution of the urban layout in this  area. The results show that the \u201cBisagno Master Plan\u201d, a territorial planning strategy aimed at  reducing geo\u2010hydrological hazard and risk, has not produced the expected benefits. In spite of the  plan,  critical  changes  in  land  use  and  the  hydrographic  network,  along  with  uncontrolled  anthropization of the Genoa metropolitan area, has continued over the last two decade

Rainfall events with shallow landslides in the Entella catchment, Liguria, northern Italy

Abstract. In recent decades, the Entella River basin, in the Liguria Apennines, northern Italy, was hit by numerous intense rainfall events that triggered shallow landslides and earth flows, causing casualties and extensive damage. We analyzed landslide information obtained from different sources and rainfall data recorded in the period 2002–2016 by rain gauges scattered throughout the catchment, to identify the event rainfall duration, D (in h), and rainfall intensity, I (in mm h−1), that presumably caused the landslide events. Rainfall-induced landslides affected the whole catchment area, but were most frequent and abundant in the central part, where the three most severe events hit on 23–24 November 2002, 21–22 October 2013 and 10–11 November 2014. Examining the timing and location of the slope failures, we found that the rainfall-induced landslides occurred primarily at the same time or within 6 h from the maximum peak rainfall intensity, and at or near the geographical location where the rainfall intensity was largest. Failures involved mainly forested and natural surfaces, and secondarily cultivated and terraced slopes, with different levels of maintenance. Man-made structures frequently characterize the landslide source areas. Adopting a frequentist approach, we define the event rainfall intensity–event duration (ID) threshold for the possible initiation of shallow landslides and hyper-concentrated flows in the Entella River basin. The threshold is lower than most of the curves proposed in the literature for similar mountain catchments, local areas and single regions in Italy. The result suggests a high susceptibility to rainfall-induced shallow landslides of the Entella catchment due to its high-relief topography, geological and geomorphological settings, meteorological and rainfall conditions, and human interference. Analysis of the antecedent rainfall conditions for different periods, from 3 to 15 days, revealed that the antecedent rainfall did not play a significant role in the initiation of landslides in the Entella catchment. We expect that our findings will be useful in regional to local landslides early warning systems, and for land planning aimed at reducing landslide risk in the study area

Climatic conditions associated to the occurrence of slope instabilities in the Italian Alps in year 2016

Studies carried out in different parts of the world have shown that, in the mountain high-elevation sites, temperature can play a major role in the preparation and trigger of slope instabilities. However, the interplay with other climatic parameters (in particular precipitation) and the nature of the climate-driven processes that lead to the development of slope instability continue to be poorly understood. This understanding is crucial in order to define reliable scenarios of the evolution of slope instability under the expected climatic and environmental changes. The present work aims to contribute to shed light on these issues by analyzing with the statistical and probabilistic method developed by Paranunzio et al. (2016) the values of the climatic parameters associated to the most significant events of slope instability occurred at high elevation in the Italian Alps in 2016. The method allows to detect the anomalies in temperature and precipitation values that are associated to the development of these slope instabilities, providing the ground for discussion of possible causes and triggering mechanisms, also in the framework of ongoing climate change. Paranunzio R., Laio F., Chiarle M., Nigrelli G., Guzzetti F. (2016) - Climate anomalies associated to the occurrence of rockfalls at high-elevation in the Italian Alps. Natural Hazards and Earth System Sciences, 16, 2085-2106, DOI: 10.5194/nhess-16-2085-2016

Historical Geomorphological Research of a Ligurian Coastal Floodplain (Italy) and Its Value for Management of Flood Risk and Environmental Sustainability

The alluvial plain of the Entella River (Eastern Liguria), historically affected by damaging flood events, has been heavily modified over the past 250 years by human activity and natural processes. A qualitative and quantitative analysis of the morphological and land use evolution of the Entella floodplain since the 18th century was carried out using base maps and aerial photos ranging from 1758 to 2016. These diverse sources were Geographical Information System (GIS) georeferenced. Additional information on land-use change was gathered from historical documents and recent research reports. The main transformations to the floodplain include morphological changes, e.g., narrowing, channelization, displacement of the river channel and the advance of the coastal line due to fills and embankments. In addition, there has been very significant urbanization with loss of vegetated and agricultural areas. Our results indicate the primary role of human disturbance on morphological changes and landscape modifications of the coastal floodplain, particularly over the last 200 years. Furthermore, the historical geomorphological and cartographical analysis we adopted to reconstruct the floodplain transformation represents an essential tool in flood risk mitigation and environmental sustainability management, particularly in an urbanized coastal plain historically affected by floods

Implementation of Nature-Based Solutions for Hydro-Meteorological Risk Reduction in Small Mediterranean Catchments: The Case of Portofino Natural Regional Park, Italy

Nature-based solutions (NBS) are usually defined as complementary or alternative solutions to \u201cgrey infrastructures\u201d (traditionally made with cement) aimed at conserving and regenerating the functionality of natural and semi-natural ecosystems. The research to date shows a considerable potential of NBS to address the current challenges related to climate change and geo-hydrological risks. Despite significant interest in NBS by researchers and practitioners, knowledge concerning their practical implementation, monitoring, and evaluation is still lacking. This is particularly true for large-scale NBS. The present paper discusses how such solutions can be implemented in the context of hydro-meteorological risk reduction in small Mediterranean catchments with a strong tourist vocation. The work presented here is situated within the RECONECT Project (Regenerating ECOsystems with Nature-based solutions for hydro-meteorological risk rEduCTion), which aims to contribute to a European reference framework on NBS by demonstrating, upscaling, and replicating large-scale NBS in rural and natural areas. The Italian case study of RECONECT is the Portofino Natural Regional Park, which represents a unique natural landscape element with high ecologic, social, and economic (touristic) value, which is threatened by a range of geo-hydrological hazards, such as flash floods, hyper-concentrated floods, shallow landslides, rockfalls, and storm surges. This paper also presents details of NBS interventions in two pilot catchments (San Fruttuoso and Paraggi) visited by thousands of tourists throughout the year. It addresses some of the key aspects related to monitoring meteorological and hydrological processes, as well as remote sensing activities (i.e., LiDAR surveys), which are necessary for the identification of critical-instability areas along waterways and the reconstruction of dry stone walls. Lastly, a discussion of relevant mitigation and adaptation strategies that are potentially replicable at national and international levels is also provide

Extreme rainfall events: evaluation with different instruments and measurement reliability

With regard to extreme events, it is known that an intensity of about 1 mm/min already represents an extreme intensity. Under alpine conditions, a precipitation event with intensity about 3 mm/min has occurred. Therefore the rain gauges in this region have to be able to measure in this and even in higher intensity ranges. This study deals with basically automated Tipping Bucket Rain (TBR) gauge, and Bulk precipitation samplers, which allows to hold back more than 95% of the cumulative rainfall that are verified within the space of the week without losses during the extreme events and with a minimum evaporation loss. In the last 10 years analysed, for a total of 221 extreme events, in 110 extreme events the Bulk samplers have collected rainfall more than automated TBR. In 17 extreme events an underestimation more than 10% was evaluated. The objective was to single out the counting errors associated with TBR gauge, during extreme events, so as to help the understanding of the measured differences between instruments in the field. We want to prove if the automated precipitation gauge, is or not, a reliable and precise device of measurements precipitation with particular interest regarding heavy and extreme events

The Role of Soil Type in Triggering Shallow Landslides in the Alps (Lombardy, Northern Italy)

Shallow landslides due to the soil saturation induced by intense rainfall events are very common in northern Italy, particularly in the Alps and Prealps. They are usually triggered during heavy rainstorms, causing severe damage to property, and sometimes causing casualties. A historical study and analysis of shallow landslides and mud-debris flows triggered by rainfall events in Lombardy was carried out for the period of 1911–2010, over an area of 14,019 km2. In this study, intensity–duration rainfall thresholds have been defined using the frequentist approach, considering some pedological characteristics available in regional soil-related databases, such as the soil region, the textural class, and the dominant soil typological units (STU). The soil-based empirical rainfall thresholds obtained considering the soil regions of the study area were significantly different, with a lower threshold for landslide occurrence in the soil region M1 (Alps), where soils developed over siliceous parent material, with respect to the whole study area and the soil region M2 (Prealps), where soils developed over calcareous bedrocks. Furthermore, by considering textural classes, the curves were differentiated, with coarse-textured soils found more likely to triggerlandslides than fine soils. Finally, considering both texture and main soil groups, given the same rainfall duration, the rainfall amount and intensity needed to initiate a landslide increased in the following order: “coarse-skeletal” Cambisols < Umbrisols < Podzols < “fine” Cambisols. The results of this study highlighted the relevant role of pedological conditioning factors in differentiating the activation of rainfall-induced shallow landslides in a definite region. The information on soils can be used to define more precise rainfall–pedological thresholds than empirical thresholds based solely on meteorological conditions, even when they are locally defined. This knowledge is crucial for forecasting and preventing geo-hydrological processes and in developing better warning strategies to mitigate risks and to reduce socio-economic damage