Avalanche risk management using GRASS GIS

The GRASS system has been used to evaluate avalanche risk. This has been done by combining heterogeneous data. Val di Pejo, located in the north-western Trentino, an Italian alpine region which shows frequent and sometimes huge avalanche phenomena, has been selected as test area. A morphologic risk has been defined in those areas where the slope is between 28° and 55° for a minimum surface of about 625 m with an upstream slope change greater than 10°. An algorithm which uses these morphologic rules has been developed and applied using the GRASS MAPCALC feature to obtain a map of the "morphologic risk", i.e. areas showing an avalanche probability based only on their geometric features. The ability of the vegetation to protect against the avalanche phenomena has been evaluated by recognizing three different coverage types depending on their density, since the latter influences their ability to avoid the creation of a compact and homogeneous snow layer. A map of the vegetation’s protection ability has been obtained. vegetation types has been obtained using the information of the Trento’s Forest Management Bureau. The boundaries of the vegetation types in the maps used for forest management are generally approximated, so it has been necessary to verify the real extension of the different kinds of vegetation. An orthophoto has been obtained by differential rectification of digitalized aerial photographs using the DTM and some control points in GRASS. The orthoimages have been used to test the real location of the boundaries and the extension of the parcels. The real ability of the different vegetation classes to offer protection against avalanches has been evaluated comparing the morphologic avalanche risk area with the extension of the events occurred. The ratio between the real surface covered by avalanches on the C.L.P.V. "Carta di Localizzazione Probabile delle Valanghe" (C.L.P.V. Possible Avalanche Location Map) and the potential surface obtained following the described criteria, divided in three different vegetation classes, highlights the importance of the vegetation coverage in protecting from avalanche risk.