Petrucci, Olga

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.

In the present work, for a study area located in the southernmost province of continental Italy, data concerning the historical series of floods which have occurred since XVII century have been collected. Damages caused by flood events were discussed together with rainfall regime and trend (for the period in which data are available) and with main modifications due to variations in population number. The aim was to assess if the frequency of damaging floods is changing and if there is a role of rainfall and/or of anthropic modifications of land use on these changes. 150 damaging floods were analysed; 4% of the total were floods which caused damages to people, and which mainly occurred in the past centuries. Notwithstanding, the trend of damaging floods is increasing due to the effects of floods observed in the last decades. At the same time, the rainfall trend is generally decreasing, as observed at regional scale, and not significant to justify the flood recurrence increase. The population trend is characterised by a huge increase observed in the last decades. On this basis, the progressive urban enlargement, realised careless of both drainage network characteristics and extreme floods, can be considered as the main source of increasing risks due to damaging floods.

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 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

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 Hydrogeological Events (DHEs) are episodes of severe weather conditions characterised by strong winds, heavy rainfall, landslides, flooding, and sea storms. Each type of phenomenon developing during DHEs is characterized by a proper dynamic and, according to the social and economical framework in which develops, it can cause different impacts on people and properties. Despite during storms all these phenomena occur at the same time (or in a short while), often amplifying damage and hinting emergency management, studies available in literature tend to analyze each type of phenomenon separately, supplying a fragmentary framework of either causes (rainfall) and effects (damage). A database concerning DHEs occurred in Calabria (southern Italy) since 1800 has been recently updated, by continuing a historical research which has been started since 2000. Basing on this huge amount of data (more than 10,000 records), an analysis of the series of DHEs occurred in a selected area/period is carried out. Both the methodological framework for DHEs analysis, based on damage classification and a classification of different DHEs types are presented.

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.

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.

Landslides, floods and secondary floods (hereinafter called phenomena) triggered by rainfall and causing extensive damage are reviewed in this paper. Damaging Hydrogeological Events (DHEs) are defined as the occurrence of one or more simultaneous aforementioned phenomena. A method for the characterisation of DHEs based upon historic data is proposed. The method is aimed at assessing DHE-related hazard in terms of recurrence, severity, damage, and extent of the affected area. Using GIS, the DHEs historical and climatic data collection, the geomorphological and hydrogeological characterisation of the hit areas, the characterisation of induced damage, the evaluation of triggering rainfall return period and critical duration of each DHE were carried out. The approach was applied to a test site in Southern Italy (Calabria) for validation purposes. A database was set up including data from 24 events which have occurred during an 80-year period. The spatial distribution of phenomena was analysed together with the return period of cumulative rainfall. The trend of the occurred phenomena was also compared with the climatic trend. Four main types of Damaging Hydrogeological Events were identified in the study area.

Il complesso assetto geomorfologico della Calabria e le sue peculiarità climatiche, tra cui una piovosità maggiore della media nazionale, fanno si che questa sia una delle regioni maggiormente esposte a fenomenologie di dissesto idrogeologico. Quale effetto indiretto della rude morfologia regionale e dello sviluppo territoriale oblungo, il reticolo stradale principale ha un basso grado di interconnessione, circostanza questa che ne amplifica l’intrinseca vulnerabilità. In tale contesto, l’incidenza delle vie di comunicazione veloci e ad elevata capacità è trascurabile, mentre le tipologie costruttive risultano essere, come discusso da questo contributo, non adeguate alla diffusa vulnerabilità idrogeologica del territorio. Piogge intense e/o prolungate determinano la frequente insorgenza di crisi territoriali, comunemente definite eventi alluvionali, che determinano sia frane diffuse che catastrofiche piene, e causano perdite di vite umane nonchè gravi e duraturi danni alle infrastrutture di trasporto. In tali circostanze, i dissesti che si determinano lungo la rete viaria rappresentano una fonte di danno sia diretto che indiretto per la comunità e nei casi più gravi costituiscono un impedimento alle attività di protezione civile. L’analisi sistematica delle tipologie di dissesti che hanno interessato la rete viaria in un arco temporale sufficientemente esteso (80 anni), selezionato per la sua significatività, costituisce uno strumento per la valutazione delle relazioni causa effetto fra il verificarsi di piene ed eventi alluvionali da una parte e l’insorgenza dei dissesti della rete viaria dall’altra. La ricerca si propone di individuare indicazioni utili alla programmazione della manutenzione ordinaria e nonché alla gerarchizzazione delle priorità degli interventi volti a minimizzare i danni causati dalle piene alle infrastrutture lineari di trasporto.