The Weight of Evidence Statistical Method in Landslide Susceptibility Mapping of the Rio Pardu Valley (Sardinia, Italy)

The landslide susceptibility of hillsides has been assessed using the statistical methodology known as Weight of Evidence. The chosen area for applying the method is the Valley of the Pardu River, placed in the eastern-central part of Sardinia, Italy, which turns out to be one of more hazardous zone in Sardinia. The Weight of Evidence method has been implemented by means of the ArcView 3.2 software and the ArcSDM extension. The landslides map has been digitized, georeferenced and supplemented by observation of the 2006 orthophoto at colors.

For evaluating the landslide susceptibility of the studied area, the basic parameters of the landslide susceptibility have been taken into consideration: lithology, land use and slope.

In order to check the reliability and the forecasting capability of the method, the influence of each parameter on the instability phenomena has been calculated analyzing an area sample, obtained by extracting in random way a little percentage of the studied territory. In the sampled area the same proportion between the area affected by landslides and the total area calculated on the whole territory, equal to about the 0.063%, has been kept. Two subsets have been so created: the Training set and the Validation set. The Training set has been divided into two subgroups: the subgroup of the areas which do not present landslide phenomena and the subgroup of the areas which present landslide phenomena.

Then a statistical analysis of different parameters has been carried out, using the algorithms of the Weight of Evidence method: in such a way the weights to be attributed to each class of every single parameter have been obtained.

To validate the results of the analysis, the map of the hillside instability obtained with the method of the Weight of Evidence and the map of the landslide phenomena have been compared.