Fausto Guzzetti

Landslide hazard evaluation: a review of current techniques and their application in a multi-scale study, Central Italy

In recent years, growing population and expansion of settlements and life-lines over hazardous areas have largely increased the impact of natural disasters both in industrialized and developing countries. Third world countries have difficulty meeting the high costs of controlling natural hazards through major engineering works and rational land-use planning. Industrialized societies are increasingly reluctant to invest money in structural measures that can reduce natural risks. Hence, the new issue is to implement warning systems and land utilization regulations aimed at minimizing the loss of lives and property without investing in long-term, costly projects of ground stabilization. Government and research institutions worldwide have long attempted to assess landslide hazard and risks and to portray its spatial distribution in maps. Several different methods for assessing landslide hazard were proposed or implemented. The reliability of these maps and the criteria behind these hazard evaluations are ill-formalized or poorly documented. Geomorphological information remains largely descriptive and subjective. It is, hence, somewhat unsuitable to engineers, policy-makers or developers when planning land resources and mitigating the effects of geological hazards. In the Umbria and Marche Regions of Central Italy, attempts at testing the proficiency and limitations of multivariate statistical techniques and of different methodologies for dividing the territory into suitable areas for landslide hazard assessment have been completed, or are in progress, at various scales. These experiments showed that, despite the operational and conceptual limitations, landslide hazard assessment may indeed constitute a suitable, cost-effective aid to land-use planning. Within this framework, engineering geomorphology may play a renewed role in assessing areas at high landslide hazard, and helping mitigate the associated risk.

Gis Technology in Mapping Landslide Hazard

In the recent years, the ever-increasing diffusion of GIS technology has facilitated the application of quantitative techniques in landslide hazard assessment. Today a wider spectrum of instability causal factors, mainly morphological and geological in nature, can be cost-effectively acquired, stored and analysed in digital form. In particular, by processing elevation data and its derivatives new morphometric parameters can be readily generated over wide regions, and used as predictors of landslide occurrence. Despite the potential of such technological advancements, landslide hazard mapping remains a major, largely unsolved task. The identification and mapping of past and present landslide bodies, which constitute fundamental steps for predicting future slope-failures, remain highly subjective. Likewise, many basic instability determinants cannot be acquired and mapped with adequate accuracy. Most of the current methods for manipulating instability factors and evaluating hazard levels remain error-prone or questionable.

Landslide fatalities and the evaluation of landslide risk in Italy

A database of landslides that occurred in Italy between 1279 and 1999 and caused deaths, missing people, injuries and homelessness was compiled from a variety of different sources. These included the archive of the National Research Councils AVI (Damaged Urban Areas) project, which compiled information on landslide events in the 20th century in Italy. The sources also included reports on historical landslide investigations for the whole of Italy, Alpine areas, the Apennines, various regions or provinces, and for single sites. Analysis of the database indicates that more than 10,000 people died in a total of 840 landslide events. Fatal landslide events were more frequent in the Alpine regions of Northern Italy and in Campania (southern Italy), and most casualties occurred in the Autumn. Fast-moving landslides caused the largest number of deaths. They included rockfalls, rockslides, rock avalanches and debris flows. The cumulative frequency of landslide events was plotted against their consequences, and the plots were compared to similar curves for the whole Alps and for Canada, Japan, China and Hong Kong. The frequency in Italy was found to be higher than in the Alps, Canada and Hong Kong, but lower than that of Japan and China. Landslide mortality rates were estimated and compared to mortality rates for other natural, medical, and human-induced hazards.

Power-law correlations of landslide areas in central Italy

Abstract We have studied the frequency–area statistics of landslides in central Italy. We consider two data sets. Data set A contains 16 809 landslide areas in the Umbria–Marche area of central Italy; they represent a reconnaissance inventory of very old, old, and recent (modern) landslides. The noncumulative frequency–area distribution of these landslides correlates well with a power-law relation, exponent −2.5, over the range 0.03 km 2 A L 2 . Data set B contains 4233 landslides that were triggered by a sudden change in temperature on 1 January 1997, resulting in extensive melting of snow cover. An inventory of these snow-melt-triggered landslides was obtained from aerial photographs taken 3 months after the event. These landslides also correlate well with a power-law relation with exponent −2.5, over the range 0.001 km 2 A L 2 . We show that the correlation of data set B is essentially identical to the correlation of 11 000 landslides triggered by the 17 January 1994 Northridge, California earthquake. We attribute a rollover for small landslides in data set A to incompleteness of the record due to erosion and other processes, and to limitations in the reconnaissance mapping technique used to complete the inventory. On the other hand, we conclude that rollovers for small landslides in data set B and the California earthquake data are real and are associated with the surface morphology. We conclude that the power-law distribution is valid over a wide range of landslide areas and discuss possible reasons. We also discuss the contribution of the snow-melt- and earthquake-triggered landslide events to the total landslide inventory.

Use of GIS Technology in the Prediction and Monitoring of Landslide Hazard

Technologies such as Geographical Information Systems (GIS) have raised great expectations as potential means of coping with natural disasters, including landslides. However, several misconceptions on the potential of GIS are widespread. Prominent among these is the belief that a landslide hazard map obtained by systematic data manipulation within a GIS is assumed to be more objective than a comparable hand-made product derived from the same input data and founded on the same conceptual model. Geographical data can now be handled in a GIS environment by users who are not experts in either GIS or natural hazard process fields. The reality of the successful application of GIS within the landslide hazard domain seems to be somewhat less attractive than current optimistic expectations.In spite of recent achievements, the use of GIS in the domain of prevention and mitigation of natural catastrophes remains a pioneering activity. Diffusion of the technology is still hampered by factors such as the difficulty in acquiring appropriate raw data, the intrinsic complexity of predictive models, the lack of efficient graphical user interfaces, the high cost of digitisation, and the persistence of bottlenecks in hardware capabilities.In addition, researchers are investing more in tuning-up hazard models founded upon existing, often unreliable data than in attempting to initiate long-term projects for the acquisition of new data on the causes of catastrophic events. Governmental institutions are frequently involved in risk reduction projects whose design and implementation appear to be governed more by political issues than by technical ones. There is an unfortunate general tendency to search for data which can be collected at low cost rather than attempting to capture the information which most readily explains the causes of a disaster.If the technical, cultural, economic and political reasons for this unhealthy state cannot be adequately tackled, the International Decade for Natural Disaster Reduction will probably come to an end without achieving significant advances in the prediction and control of natural disasters.

The AVI project: A bibliographical and archive inventory of landslides and floods in Italy

The AVI project was commissioned by the Minister of Civil Protection to the National Group for Prevention of Hydrogeologic Hazards to complete an inventory of areas historically affected by landslides and floods in Italy. More than 300 people, divided into 15 research teams and two support groups, worked for one year on the project. Twenty-two journals were systematically searched for the period 1918–1990, 350,000 newspaper issues were screened, and 39,953 articles were collected. About 150 experts on mass movement and floods were interviewed and 1482 published and unpublished technical and scientific reports were reviewed. The results of the AVI project, in spite of the limitations, represent the most comprehensive archiving of mass movement and floods ever prepared in Italy. The type and quality of the information collected and the methodologies and techniques used to make the inventory are discussed. Possible applications and future developments are also presented.

STONE: a computer program for the three-dimensional simulation of rock-falls

Rock-fall poses a continuous hazard in mountain areas worldwide. Despite the fact that rock fall is a simple landslide type to model, only a few attempts have been made to establish rock-fall hazard and the associated risk at regional scales. We developed a three-dimensional simulation program that generates simple maps useful to assess rockfall hazard, using GIS technology to manipulate existing thematic information available in digital format. The program requires as input a digital terrain model, the location of rock-fall detachment areas, the dynamic friction coefficient used to simulate the loss of velocity during rolling, and the coefficients for normal and tangential energy restitution at the impact points. The program allows for the natural variability of the input data by using a random component approach. Raster outputs include the count of rock-fall trajectories, the maximum velocity and the maximum height computed at each grid cell. Vector outputs consist of the planar (two dimensional) and the three-dimensional trajectories of the rock falls. The program outputs proved to be consistent with the results of other rock-fall simulation programs, to be reliable for modelling rock-fall in three-dimensional geomorphological settings, and to help in the quantitative assessment of rock-fall hazard over large areas.

Tier-based approaches for landslide susceptibility assessment in Europe

In the framework of the European Soil Thematic Strategy and the associated proposal of a Framework Directive on the protection and sustainable use of soil, landslides were recognised as a soil threat requiring specific strategies for priority area identification, spatial hazard assessment and management. This contribution outlines the general specifications for nested, Tier-based geographical landslide zonings at small spatial scales to identify priority areas susceptible to landslides (Tier 1) and to perform quantitative susceptibility evaluations within these (Tier 2). A heuristic, synoptic-scale Tier 1 assessment exploiting a reduced set of geoenvironmental factors derived from common pan-European data sources is proposed for the European Union and adjacent countries. Evaluation of the susceptibility estimate with national-level landslide inventory data suggests that a zonation of Europe according to, e.g. morphology and climate, and performing separate susceptibility assessments per zone could give more reliable results. To improve the Tier 1 assessment, a geomorphological terrain zoning and landslide typology differentiation are then applied for France. A multivariate landslide susceptibility assessment using additional information on landslide conditioning and triggering factors, together with a historical catalogue of landslides, is proposed for Tier 2 analysis. An approach is tested for priority areas in Italy using small administrative mapping units, allowing for relating socioeconomic census data with landslide susceptibility, which is mandatory for decision making regarding the adoption of landslide prevention and mitigation measures. The paper concludes with recommendations on further work to harmonise European landslide susceptibility assessments in the context of the European Soil Thematic Strategy.

Improving predictive power of physically based rainfall-induced shallow landslide models: a probabilistic approach

Distributed models to forecast the spatial and temporal occurrence of rainfall-induced shallow landslides are based on deterministic laws. These models extend spatially the static stability models adopted in geotechnical engineering, and adopt an infinite-slope geometry to balance the resisting and the driving forces acting on the sliding mass. An infiltration model is used to determine how rainfall changes pore-water conditions, modulating the local stability/instability conditions. A problem with the operation of the existing models lays in the difficulty in obtaining accurate values for the several variables that describe the material properties of the slopes. The problem is particularly severe when the models are applied over large areas, for which sufficient information on the geotechnical and hydrological conditions of the slopes is not generally available. To help solve the problem, we propose a probabilistic Monte Carlo approach to the distributed modeling of rainfall-induced shallow landslides. For the purpose, we have modified the Transient Rainfall Infiltration and Grid-Based Regional Slope-Stability Analysis (TRIGRS) code. The new code (TRIGRS-P) adopts a probabilistic approach to compute, on a cell-by-cell basis, transient pore-pressure changes and related changes in the factor of safety due to rainfall infiltration. Infiltration is modeled using analytical solutions of partial differential equations describing one-dimensional vertical flow in isotropic, homogeneous materials. Both saturated and unsaturated soil conditions can be considered. TRIGRS-P copes with the natural variability inherent to the mechanical and hydrological properties of the slope materials by allowing values of the TRIGRS model input parameters to be sampled randomly from a given probability distribution. [..]

Large alluvial fans in the north-central Po Plain (Northern Italy)

Abstract Seventeen alluvial fans in the Po Plain, between the Ticino and Mincio Rivers, in Northern Italy were identified and studied. The research was carried out following a semi-quantitative approach that combined display and analysis of altitude data, interpretation of morphometrical maps, and comparative inspection of geomorphological maps. Boundaries between fans were drawn interactively on a shaded relief image, computed from a 50 m resolution digital terrain model prepared interpolating 5 and 1 metre contour lines. For each fan, or for each portion making up a larger fan, geometric and morphometric criteria were computed. Fan morphometric criteria were compared to the present drainage basins morphological setting. The relationship between fan area and drainage basin area shows positive allometry, with the slope of the regression line lower than that commonly proposed for both arid and humid regions.