Petrucci, Olga

E’ stata effettuata una ricerca per ricostruire la serie storica delle piene verificatesi a partire dal XVII secolo in un settore della Calabria sud-occidentale coincidente con il comune di Reggio Calabria. Dei 150 eventi di piena costituenti la serie, il 4% è responsabile di danni alla popolazione, mentre nei restanti casi i danneggiamenti sono a carico di infrastrutture, opere idrauliche ed edilizia. La serie storica è stata analizzata congiuntamente ai dati di pioggia (per il periodo in cui essi sono disponibili) e alle principali modificazioni legate all’incremento demografico dell’area analizzata. Lo scopo è di valutare se la frequenza delle piene responsabili di danni è cambiata durante il periodo analizzato e il ruolo esercitato su tale frequenza dalle piogge e dalle modificazioni antropiche del territorio. L’analisi evidenzia che il trend delle piene in grado di generare danni è in crescita, mentre il trend delle piogge, come osservato anche a scala regionale, è in diminuzione. Al contrario, i trend della popolazione e dell’espansione urbanistica mostrano una crescita, molto marcata negli ultimi decenni. L’incremento delle piene catastrofiche appare, dunque, connesso più alla progressiva urbanizzazione delle aree inondabili che alle modificazioni della piovosità.

Damaging Hydro-geologic Events (DHEs), de- fined as landslides and floods caused by heavy or prolonged rainfall, represent an important source of economic damages. We propose an approach to classify DHEs, considering 1) meteorological antecedent conditions, 2) the season during which the event occurs, 3) the return period of maximum daily rainfall triggering the event, 4) geographic sectors hit, 5) types of triggered damaging phenomena; and 6) induced damage. We applied this approach to a case study of time series of DHEs that occurred over 85 years in Calabria (southern Italy). We analysed 13 DHEs that, between 1921 and 2005, triggered landslides, floods and secondary floods, causing severe damage and tens of causalities all over the Calabria region. During the analysed events, 64% of Calabria’s municipalities suffered many types of damage. The most relevant rain phenomena and the largest damages were caused by the persistent effects of perturbations on Calabria, which were preceded by the appearance of low-pressure fields in two different areas located westwards. We sorted the events into three types based on geographic damage distribution and types of triggered phenomena and induced damage. The first two types are characterised by similar severity levels, while the third shows the highest severity, in terms of both damage and victims. Independent of the type of event, the S-SE and E sectors of the region are the most frequently affected by DHEs. As regards human life, floods are the most dangerous type of phenomenon, causing the highest number of fatalities. Our analysis indicates a decreasing frequency of DHEs during the study period, and an absence of the most severe type for more than 50 years. The number of victims is also decreasing over time.

Past Damaging Hydrogeological Events (DHEs), which can be defined as periods characterised by heavy rainfall inducing such damaging phenomena as landslides and floods, are analysed in this article. The work is focused on the relationships between these phenomena and the characteristics of triggered rainfall, to supply useful suggestions for early detection and damage mitigation. The analysis of past DHEs allows for the characterisation of the main types of DHEs, which affected a selected area in the past and could affect it again in the future. The proposed characterisation is based on triggering scenarios (meteorological conditions preceding the occurrence of DHEs), DHE‘s effects (damage caused by landslides and floods) and triggering factors (rainfall of different durations). Based on these features, the typical DHEs affecting a study area can be outlined and ranked according to their severity, thus specific emergency management can be planned to successfully manage them. To obtain results that have a reliable statistical meaning, a large amount of data of three different types (meteorological, rainfall and damage data) must be treated, and some indices, allowing the comparative analysis of these kinds of data, have to be introduced. In this work we describe the methodological approach, which can be applied in different climatic and anthropogenic contexts;finally, some applications of the proposed method to the region of Calabria (South Italy) are presented

South-Eastern Calabria is among the areas in Southern Italy which are hardest hit by heavy and relentless rainfalls able to induce geomorphological phenomena sometimes resulting in widespread damage. The Catastrophic Geomorphological Events which have occurred over a time period of 67 years across an area of about 700 Km2 are characterised with a view to correlating major phenomena, such as landslides and flooding, with heavy rains and anthropic expansion. Igneous, metamorphic and sedimentary rocks outcrop and slope stability phenomena affecting the area vary in density and frequency accordingly. Induced phenomena are divided in landslides, floods and “secondary floods”. The analysis of historical precipitation series highlighted the space and time distribution of rainfalls, determining their exceptionality as return period of daily cumulative rainfall of different duration, with respect to the various disastrous phenomena triggered. The aim of this study is to predict different scenarios characterised by various severity levels related to rainfall return periods.

A period of bad weather conditions due to prolonged intense rainfall and strong winds can trigger landslides, floods, secondary floods (accumulation of rain on surfaces with low permeability), and sea storms, causing damage to humans and infrastructure. As a whole, these periods of bad weather and triggered phenomena can be defined as damaging hydrogeological events (DHEs). We define a methodological approach based on seven simple indexes to analyze such events. The indexes describe the return period (T) and trend of rainfall, the extent of hit areas, and the level of damages; they can be considered attributes of georeferenced features and analyzed with GIS techniques. We tested our method in an Italian region frequently hit by DHEs. In a period of 10 years, 747 damaging phenomena (landslides, 43%; floods, 38%) and 94 DHEs have been classified. The road network and housing areas are the most frequently damaged elements, threatened by all types of damaging phenomena. T classes are almost in accordance with the level of damage. These results can be used to outline warning levels for civil protection purposes, to forecast the areas most likely to be hit and the potential ensuing damage, to disseminate information concerning vulnerable areas, and to increase people’s awareness of risk

A methodological experience dealing with delimitation of flood-prone-areas has been described. After the illustration of methodological approach, a case study concerning a Calabria area is presented. In this region of Southern Italy, the river network is made of ephemeral streams characterised by flash floods and huge bed-load. The methodology develops in four main steps: 1) a detailed research about historical flood events and induced damages on a temporal window of about 400 years; 2) the multi-temporal observation of morphological river geometry, carried out using maps and air-photos of different epochs; 3) the statistical characterisation of maximum rainfall that can be expected in the study area; 4) the evaluation of stream water depth for different return period flow. The results obtained point out that, in the study area, during the analysed period, flood risk is increased, mainly because of the urban growth. Improvements to the obtained results, can be obtained assessing and taking into account the modifications induced by engineering works.

L’assetto geomorfologico e le condizioni climatiche fanno della Calabria una delle regioni maggiormente vulnerate da fenomeni franosi. Il reticolo viario di questa regione, che attraversa ampi settori a elevata pericolosità da frana, presenta lunghi tratti con tipologie costruttive concepite nel corso della prima metà del secolo scorso e mai soggette a un sostanziale ammodernamento, così come osservato per altre aree dell’Italia meridionale (Sdao & Polemio 2000). Dal punto di vista della stabilità delle scarpate e dei principali manufatti, gli accorgimenti costruttivi sono spesso essenziali e le opere di sostegno di limitata estensione, lasciando esposta una porzione molto estesa della rete. D’altra parte, anche i tratti di più moderna realizzazione si sono dimostrati drammaticamente vulnerabili in virtù della spiccata propensione al dissesto idrogeologico del territorio calabrese. Il complesso di tali effetti ha causato frequenti e ingenti danni, specialmente nel corso di stagioni invernali durante le quali piogge intense e prolungate determinano l’insorgenza di crisi territoriali comunemente definite eventi alluvionali (Petrucci & Polemio 2003, Petrucci et al. 2009). In tali circostanze i dissesti che si determinano lungo la rete viaria rappresentano una fonte di danno sia diretto che indiretto per la comunità. Nei casi più gravi sono tali da costituire persino un impedimento alle attività di protezione civile, mentre, in situazioni di minore gravità, ostacolano comunque il ripristino della normale mobilità. L’analisi della serie storica dei fenomeni franosi che hanno interessato la rete viaria di un settore territoriale della regione durante un arco temporale di significativa estensione (1921-1997 nel caso di studio) può costituire, in questo contesto, uno strumento in grado di mettere facilmente in luce i punti critici del sistema viario, fornendo altresì indicazioni di dettaglio sulle principali tipologie di frane da temere e sulle condizioni pluviometriche che ne determinano l’innesco. Una volta individuati i tratti più frequentemente e/o intensamente vulnerabili, tali conoscenze rappresentano la base per la pianificazione sia della messa in sicurezza che della gestione delle emergenze, unitamente alla previsione della manutenzione straordinaria.

A methodological approach based on analysing landslides that occurred over a long period and climatic data characterizing that period is presented. The method investigates whether there are any effects of climate on landslide triggering. The approach has been tested in Calabria (Italy). Both landslide and climatic data have been obtained from available databases that have been expanded. Landslide data came from historical archives and newspapers, whereas the climatic analysis is based on daily and monthly series of rainfall and temperature. The method simplifies the comparative analysis of several time series by defining some indices (the monthly, bi-monthly ... m-monthly indices of precipitation, temperature, wet days and precipitation, and the monthly landslide number) that can be used to study phenomena, such as landslides, that are characterized by spatial and temporal variability. For Calabria, the number of landslides is correlated to monthly precipitation, wet days and precipitation intensity. Thus, landslide occurrence could be roughly forecast using these climatic data. Despite the favourable climatic trend, landslides are not decreasing because the recent utilization of landslide-prone areas increases the vulnerability.

Rainfall is the most common cause of landslides. The cost of Rainfall Triggered Landslides (RTL) is not well documented and often unobtainable. In areas where they do not pose a threat to life, great damage is caused to farmland and communication infrastructures and pasture bio-mass production is heavily reduced (Table 1). In Japan more than 10,000 RTL are reported every year which claim the lives of some 400 persons (Fukuoka, 1980); A single event has killed 100 persons and inflicted property damages estimated at 300 billion yen Shimizu (1988). Given the importance of the topic, some 138 papers dealing with RTL were selected and key information was collected in a database. Nearly 82 % of all records are local investigations carried out in 23 countries. Italy provides the largest sample as for authors' nationality and widespread proneness to landslides; followed by United States (15 %), Hong Kong (8 %), Japan and United Kingdom. About 21 % of all selected papers are methodological research or syntheses and comparisons of different methodologies. Investigations refer to widespread landsliding (69 % of AD) (that is the Available Data number for each database field), the remainder corresponds to single or few landslides. A landslide classification proposed by Hutchinsons (1995) and based on the maximum depth of failure (Vm), is adopted in this work. About 40 % of AD are intermediate or deep-seated landslides (Vm > 10 m), that include all reactivations, the rest are shallow or superficial landslides, generally first-time movements. The most frequent types are: flows, translational and rotational slides, slips, avalanches and creep, decreasing order (Cruden & Varnes 1996) with soil or debris generally constituting the landslide bodies. Daily (54 % of AD), hourly (28 %), monthly (15 %) and yearly (4 %) rainfalls are used as input. Roughly 49 % consider cumulative rainfall (a rain water height obtained adding regularly monitored rainfall) of different duration. The prevalent approach is empirical, statistical or hydrological-qualitative; one out of four is partially physical and often uses numerical modelling. About 10 % combine rainfall effect characterisation with geotechnical stability analysis. The results of research in progress have been summarised.

A natural hazard is a geophysical, atmospheric or hydrological event (e.g., earthquake, landslide, tsunami, windstorm, flood or drought) that has the potential to cause harm or loss, while a natural disaster is the occurrence of an extreme hazard event that impacts on communities causing damage, disruption and casualties, and leaving the affected communities unable to function normally without outside assistance (Twig, 2007). The definition of natural disaster impact (NDI) can change according to both the aim of the study and the scientist assessing it. It can be defined as constituting the direct, indirect and intangible losses caused on environment and society by a natural disaster (Swiss Re, 1998). Direct losses include physical effects such as destruction and changes that reduce the functionality of an individual or structure. Damages to people (death/injury), buildings, their contents, and vehicles are included, as are clean-up and disposal costs. Indirect losses affect society by disrupting or damaging utility services and local businesses. Loss of revenue; increase in cost; expenses connected to the provision of assistance, lodging, and drinking water; and costs associated with the need to drive longer distances because of blocked roads are included. Intangible losses include psychological impairments caused by both direct and intangible losses that individuals personally suffer during the disaster. The Natural Disaster Impact Assessment (NDIA) is crucial in helping individuals to estimate replacement costs and to conduct cost-benefit analyses in allotting resources to prevent and mitigate the consequences of damage (UNEP-ECLAC, 2000). A general NDIA procedure has not yet been developed; several approaches are available in literature and their applicability depends on the accessibility of damage data. Possible end users of NDIA include the following (Lindell & Prater, 2003): 1. Governments, with an interest in estimating direct losses to report to taxpayers and to identify segments of the community that have been (or might be) disproportionately affected 2. Community leaders, who may need to use loss data after a disaster strikes to determine if external assistance is necessary and, if so, how much. 3. Planners, who can develop damage predictions to assess the effects of alternative hazard adjustments. Knowing both the expected losses and the extent to which those losses could be reduced makes it possible to implement cost-effective mitigation strategies. 4. Insurers, who need data on the maximum losses in their portfolios to guarantee their solvency or even to undertake additional measures to alleviate the risk that they would face in case of a disaster (i.e., the use of catastrophe bonds which are risk-linked securities that transfer a specified set of risks from a sponsor to investors) (Noy & Nualsri, 2011). Data availability and reliability, especially for old events, represent constraints in the NDIA context because of several issues of very different type: 1. Data availability, for current events, depends on the time at which data gathering started. It is impossible to decide a priori when data have to be gathered: it primarily depends on the type of phenomenon causing the disaster and its magnitude, and secondly on the scope of the assessment (for example, the assessment should not be unnecessarily delayed as there is an urgent need to elicit support from the international community) (ECLAC, 2003). 2. Long-term losses must sometimes be determined over a period of years. Slow landslides, for example, can cause damage over long periods. Intangible damage like disaster-related stress also requires years to be detected (Bland et al., 1996). 3. In most countries, there are no agencies responsible for gathering damage data. Damage caused by severest events can be mined from international databases, while data on less severe events can be obtained by means of specific historical studies. 4. Data on property damage can depreciate the value of property, thus they would not be available or not completely reliable (Highland, 2003). 5. For some type of disasters, as landslides or floods, the costs of damages to structures such as roads are often merged with maintenance costs and are therefore not labelled as damage. In addition, when heavy rains trigger both landslides and floods (Petrucci and Polemio, 2009), it is difficult to separate landslide damage from flood damage. 6. Developing countries have an incentive to exaggerate damage to receive higher amounts of international assistance; thus, in these cases, data may not be entirely reliable (Toya & Skidmore, 2007). This chapter starts with a panoramic of the different approaches reported in the literature to assess the impact of natural disasters, and then presents some simplified approaches to perform a relative and comparative assessment of the impact caused by phenomena as landslides and floods triggered by heavy rainfall during events defined as Damaging Hydrogeological Events. Finally, some indices to assess the relative impact of landslides are presented.