Suchergebnisse

Abstract. The paper presents a methodology for relative damage assessment for historical landslide events, i.e. periods during which damage caused by rainfall-triggered landslides affected wide areas. The approach requires a minimum amount of data, and it is based on the assessment of direct, indirect and intangible damage indices at municipal and regional scale. An application to major events which occurred in Calabria (Italy) highlighted roads as the most vulnerable element, even representing the source of intangible damage for people forced to use alternative roads for their daily activities. Indirect costs seem mainly tied to displacement of people even for short periods.

Abstract. The study focuses on circumstances that affect people during periods of bad weather conditions characterised by winds, rainfall, landslides, flooding, and storm surges. A methodological approach and its application to a study area in southern Italy are presented here. A 10-yr database was generated by mining data from a newspaper. Damaging agents were sorted into five types: flood, urban flooding, landslide, wind, and storm surge. Damage to people occurred in 126 cases, causing 13 victims, 129 injured and about 782 people involved but not injured. For cases of floods, urban flooding and landslides, the analysis does not highlight straightforward relationships between rainfall and damage to people, even if the events showed different features according to the months of occurrence. The events occurring between May and October were characterised by concentrated and intense rainfall, and between May and July, the highest values of hourly (103 mm on the average) and monthly rainfall (114 mm on the average) were recorded. Urban flooding and flash floods were the most common damaging agents: injured, involved people and more rarely, cases with victims were reported. Between November and April, the highest number of events was recorded. Rainfall presented longer durations and hourly and sub-hourly rainfall were lower than those recorded between May and October. Landslides were the most frequent damaging agents but the highest number of cases with victims, which occurred between November and January, were mainly related to floods and urban flooding. Motorists represent the totality of the victims; 84% of the people were injured and the whole of people involved. All victims were men, and the average age was 43 yr. The primary cause of death was drowning caused by floods, and the second was trauma suffered in car accidents caused by urban flooding. The high number of motorists rescued in submerged cars reveals an underestimation of danger in the case of floods, often increased by the sense of security related to the familiarity of the road. In contrast, in the cases of people involved in landslides, when there was enough time to realise the potential risk, people behaved appropriately to avoid negative consequences. Of the victims, 50% were killed along fast-flowing roads; this may be related to the high speed limit in force on these roads, as a car's speed reduces the reaction time of a driver's response to an unexpected situation, whatever the damaging agent is. These results can be used in local information/education campaigns to both increase risk awareness and promote self-protective behaviours. Moreover, the mapping of damaging effects pointed out the regional sectors in which the high frequency of the events suggests further planning of in-depth examinations, which can individuate the critical points and local regulator interventions that might change damage incidences in the future.

Abstract. Landslide Periods (LPs) are defined as periods, shorter than a hydrological year, during which one or more landslide damage events occur in one or more sectors of a study area. In this work, we present a methodological approach, based on the comparative analysis of historical series of landslide damage and daily rainfall data, aiming to characterise the main types of LPs affecting selected areas. Cumulative rainfall preceding landslide activation is assessed for short (1, 2, 3, and 5 days), medium (7, 10, and 30 days) and long (60, 90, and 180 days) durations, and their Return Periods (RPs) are assessed and ranked into three classes (Class 1: RP=5-10 years; Class 2: RP=11-15; Class 3: RP>15 years). To assess landslide damage, the Simplified Damage Index (SDI) is introduced. This represents classified landslide losses and is obtained by multiplying the value of the damaged element and the percentage of damage affecting it. The comparison of the RP of rainfall and the SDI allows us to indentify the different types of LPs that affected the study area in the past and that could affect it again in the future. The results of this activity can be used for practical purposes to define scenarios and strategies for risk management, to suggest priorities in policy towards disaster mitigation and preparedness and to predispose defensive measures and civil protection plans ranked according to the types of LPs that must be managed. We present an application, performed for a 39-year series of rainfall/landslide damage data and concerning a study area located in NE Calabria (Italy); in this case study, we identify four main types of LPs, which are ranked according to damage severity.

Abstract. Damaging Hydrogeological Events are defined as periods during which phenomena, such as landslides, floods and secondary floods, cause damage to people and the environment. A Damaging Hydrogeological Event which heavily damaged Calabria (Southern Italy) between December 1972, and January 1973, has been used to test a procedure to be utilised in the zonation of a province according to damage susceptibility during DHEs. In particular, we analyzed the province of Catanzaro (2391 km2), an administrative district composed of 80 municipalities, with about 370 000 inhabitants. Damage, defined in relation to the reimbursement requests sent to the Department of Public Works, has been quantified using a procedure based on a Local Damage Index. The latter, representing classified losses, has been obtained by multiplying the value of the damaged element and the percentage of damage affecting it. Rainfall has been described by the Maximum Return Period of cumulative rainfall, for both short (1, 3, 5, 7, 10 consecutive days) and long duration (30, 60, 90, 180 consecutive days), recorded during the event. Damage index and population density, presumed to represent the location of vulnerable elements, have been referred to Thiessen polygons associated to rain gauges working at the time of the event. The procedure allowed us to carry out a preliminary classification of the polygons composing the province according to their susceptibility to damage during DHEs. In high susceptibility polygons, severe damage occurs during rainfall characterised by low return periods; in medium susceptibility polygons maximum return period rainfall and induced damage show equal levels of exceptionality; in low susceptibility polygons, high return period rainfall induces a low level of damage. The east and west sectors of the province show the highest susceptibility, while polygons of the N-NE sector show the lowest susceptibility levels, on account of both the low population density and high average rainfall characterizing these mountainous areas. The future analysis of further DHEs, using the tested procedure, can strengthen the obtained zonation. Afterwards, the results can prove useful in establishing civil defence plans, emergency management, and prioritizing hazard mitigation measures.

Abstract. In this paper, we present a methodological approach based on a comparative analysis of floods that occurred in a wide region over a long period and the climatic data characterising the same period, focusing on the climate trend. The method simplifies the comparative analysis of several time series by defining some indexes (e.g. the monthly, bi-monthly, and ... m-monthly indexes of precipitation, temperature, wet days and precipitation intensity and the monthly flood number) that can be used to study phenomena such as floods that are characterised by spatial and temporal variability. The analysis was used to investigate the potential effect of climate variation on the damaging floods trend. The approach was tested for the Calabria region (Italy) using historical flood and climatic data from 1880 to 2007. The results showed that the number of floods was correlated with the monthly indexes of precipitation, wet days, and daily precipitation intensity. The following trends were recognised: decreasing precipitation and wet days, almost constant precipitation intensity, increasing temperature, and linearly increasing floods. A second-order polynomial trend analysis showed a slight decrease in floods since the seventies, which might be explained by the favourable climatic conditions during the period and/or the effect of increasing awareness of flood vulnerability.

Abstract. The analysis of data describing damage caused by mass movements in Calabria (Italy) allowed the organisation of the Support Analysis Framework (SAF), a spreadsheet that converts damage descriptions into numerical indices expressing direct, indirect, and intangible damage. The SAF assesses damage indices of past mass movements and the potential outcomes of dormant phenomena re-activations. It is based on the effects on damaged elements and is independent of both physical and geometric phenomenon characteristics. SAF sections that assess direct damage encompass several lines, each describing an element characterised by a value fixed on a relative arbitrary scale. The levels of loss are classified as: L4: complete; L3: high; L2: medium; or L1: low. For a generic line l, the SAF multiplies the value of a damaged element by its level of loss, obtaining dl, the contribution of the line to the damage. Indirect damage is appraised by two sections accounting for: (a) actions aiming to overcome emergency situations and (b) actions aiming to restore pre-movement conditions. The level of loss depends on the number of people involved (a) or the cost of actions (b). For intangible damage, the level of loss depends on the number of people involved. We examined three phenomena, assessing damage using the SAF and SAFL, customised versions of SAF based on the elements actually present in the analysed municipalities that consider the values of elements in the community framework. We show that in less populated, inland, and affluent municipalities, the impact of mass movements is greater than in coastal areas. The SAF can be useful to sort groups of phenomena according to their probable future damage, supplying results significant either for insurance companies or for local authorities involved in both disaster management and planning of defensive measures.

Abstract. Damaging Hydro-geologic Events (DHEs), defined 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.

Abstract. A study of the effects of human modification of a coastal plain mainly involving land reclamation and flood protection is proposed. The approach involves historical, geomorphological and hydrological data as a whole, taking into account the equilibrium of rivers, plains and coastal areas. The test area, a telling example of profound economic and social transformation of a coastal plain, is the Piana di Sibari (Calabria, southern Italy), subject to major human modifications over the last 150 years. The study area, at most 300 m a.s.l., is 450 km2 wide and comprises 24 hydrographic basins. The approach is based on the creation and analysis of four databases: 1) a historical series of geo-coded flood damage (DAMAGES database), concerning damaging floods which occurred over the past few centuries in the study area; 2) a geocoded series of protection works for land reclamation, protection from floods and improvement of soil stability in steep areas (WORKS database), gathered from the archives of the agencies that carried out the works, organized in a GIS-format; 3) a historical series of maximum flood discharges and extreme rainy events (HYMAX database) aimed at defining the trends of occurrence and the intensity of flooding; 4) a coastal line position and migration over time (COASTAL database), created using mainly literature data based on discontinuous data such as historical maps and images. The work describes the complex succession of floods, protection and reclamation works, human transformation of the plain and major land use changes over the last two centuries in the test area. The new characteristics of the plain and its modifications, including major engineering works, land-use transformation and urbanisation, are illustrated. The damaging floods of the last 200 years, the modifications of runoff and flooding due to works built over the basins, hydrological data and the records concerning coastal modifications were used to create specific databases and a GIS in which these data can be analyzed by typology, location and extension. The proposed approach highlights the high degree of correlation between drainage basin management, mainly in terms of increasing protection from natural hazards, and anthropogenic development in a broad coastal plain.

Abstract. 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.

Abstract. Only a few studies have investigated the geographical and temporal variations in the frequency and distribution of rainfall-induced landslides, and the consequences of the variations on landslide risk. Lack of information limits the possibility to evaluate the impact of environmental and climate changes on landslide frequency and risk. Here, we exploit detailed historical information on landslides and rainfall in Calabria, southern Italy, between 1921 and 2010 to study the temporal and the geographical variation in the occurrence of rainfall-induced landslides and in their impact on the population. We exploit a catalogue with information on historical landslides from June 1920 to December 2010, and daily rainfall records obtained by a network of 318 rain gauges in the same period, to reconstruct 448 493 rainfall events (RE). Combining the rainfall and the landslide information, we obtain a catalogue of 1466 rainfall events with landslides (REL), where an REL is the occurrence of one or more landslide during or immediately after a rainfall event. We find that (i) the geographical and the temporal distributions of the rainfall-induced landslides have changed in the observation period, (ii) the monthly distribution of the REL has changed in the observation period, and (iii) the average and maximum cumulated event rainfall that have resulted in landslides in the recent 30-year period 1981–2010 are lower than the rainfall necessary to trigger landslides in previous periods, whereas the duration of the RE that triggered landslides has remained the same. We attribute the changes to variations in the rainfall conditions and to an increased vulnerability of the territory. To investigate the variations in the impact of REL on the population, we compared the number of REL in each of the 409 municipalities in Calabria with the size of the population in the municipalities measured by national Censuses conducted in 1951, 1981, and 2011. We adopted two strategies; the first strategy considered impact as IREL = #REL / P, and the second strategy measured impact as RREL = #REL × P, where #REL is the total number of REL in a period, and P is the size of the population in the same period and geographical area. The analysis has revealed a complex pattern of changes in the impact of rainfall-induced landslides in Calabria in the recent past, with areas where IREL and RREL have increased, and other areas where they have decreased. Municipalities where IREL has increased are mainly in the mountains, and municipalities where RREL has increased are mainly along the coasts. The complexity of the changes in the frequency and impact of rainfall-induced landslides observed in Calabria suggests that it remains difficult and uncertain to predict the possible variations in the frequency and impact of landslide in response to future climatic and environmental changes.

Abstract. This paper presents a methodological approach to both identifying and characterising Widespread Landslide Events (WLE), defined as the occurrence of several landslides through wide areas (thousands of square kilometres). This approach is based on a comparative analysis of two historical databases: a rainfall database and a landslide database, both concerning the same period. This methodology was tested on Calabria (Southern Italy) by analysing a period of more than 80 yr. The data allowed the individuation of 25 WLEs generated by the following: (a) a single rainfall event (RE), (b) a few distinct but temporarily close REs, or (c) several consecutive REs occurring over a period of up to two months. An empirical curve, obtained by interpolating the number of landslides occurred during the WLEs and the average values of cumulative rainfall that triggered them enables the individuation of the relationship between rainfall and number of landslides. The proposed methodological approach can be used wherever historical series of both rainfall and landslides are available. The results can be useful for monitoring the development of events and for the planning of emergency management.

Abstract. The NW Mediterranean region experiences every year heavy rainfall and flash floods that occasionally produce catastrophic damages. Less frequent are floods that affect large regions. Although a large number of databases devoted exclusively to floods or considering all kind of natural hazards do exist, usually they only record catastrophic flood events. This paper deals with the new flood database that is being developed within the framework of HYMEX project. Results are focused on four regions representative of the NW sector of Mediterranean Europe: Catalonia, Spain; the Balearic Islands, Spain; Calabria, Italy; and Languedoc-Roussillon, Midi-Pyrénées and PACA, France. The common available 30-yr period starts in 1981 and ends in 2010. The paper shows the database structure and criteria, the comparison with other flood databases, some statistics on spatial and temporal distribution, and an identification of the most important events. The paper also provides a table that includes the date and affected region of all the catastrophic events identified in the regions of study, in order to make this information available for all audiences.

Flood risk is dynamic and influenced by many processes related to hazard, exposure and vulnerability. Flood damage increased significantly over the past decades, however, resulting overall economic loss per event is an aggregated indicator and it is difficult to attribute causes to this increasing trend. Much has been learned about damaging processes during floods at the micro-scale, e.g. building level. However, little is known about the main factors determining the amount of flood damage on event level. Thus, we analyse and compare paired flood events, i.e. consecutive, similar damaging floods that occurred in the same area. In analogy to 'Paired catchment studies' - a well-established method in hydrology to understand how changes in land use affect streamflow – we will investigate how and why resulting flood damage in a region differed between the first and second consecutive flood events. One example are the 2002 and 2013 floods in the Elbe and Danube catchments in Germany. The 2002 flood caused the highest economic damage (EUR 11600 million) due to a natural hazard event in Germany. Damage was so high due to extreme flood hazard triggered by extreme precipitation and a high number of resulting dyke breaches. Additionally, exposure hotspots like the city of Dresden at the Elbe river as well as some smaller municipalities at the river Mulde (e.g. Grimma, Eilenburg, Bitterfeld, Dessau) were severely impacted. However, affected parties and authorities learned from the extreme flood in 2002, and many governmental flood risk programs and initiatives were launched. Considerable improvements since 2002 occurred on many levels that deal with flood risk reduction and disaster response, in particular in 1) increased flood prevention by improved spatial planning, 2) an increased number of property-level mitigation measures, 3) more effective early warning and improved coordination of disaster response and 4) a more targeted maintenance of flood defence systems and their deliberate relocation. Thus, despite higher hydrological severity damage due to the 2013 flood was significantly lower than in 2002. In our international comparative paired event study we investigate under which circumstances similar or contrasting processes occurred and hope to identify common key processes which determine flood damage on event level.