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.The experience gained from the application of multivariate models in small drainage basins, located in southern and central Italy, indicates that the type of terrain-unit selected, namely: grid-cell, unique-condition unit and slope-unit, exerts a relevant influence on the reliability and feasibility of the hazard model developed. Models, based on different types of terrain-units or statistical approaches, yield responses that may be statistically comparable but dissimilar in terms of applicability. In addition, when different landslide types occur over a region, each type requires the development of a specific model.Among the different techniques traditionally applied, multivariate approaches, although with limitations, are the most feasible and cost-effective for evaluating the landslide hazard on a regional scale. This is true if GIS techniques are fully and carefully exploited for data acquisition, processing and analysis.