Regional Scale Mapping of Debris-Flow Susceptibility in the Caminhos dos Cânions do Sul GeoPark, Southern Brazil

The UNESCO Caminhos dos Cânions do Sul Geopark, located in Southern Brazil, is an extensive territory marked by the presence of a great escarpment (Serra Geral), which is commonly affected by high magnitude mass movements. However, susceptibility studies related to such processes are scarce. As an area of geotouristic interest, it is essential to use simple  methods to support the risk and disaster management plans Thus, this work aims to compare two different methodologies The first methodology used (MI) was developed to evaluate the criticality of the basins to the development of debris flows based on five morphometric parameters (basin area, percentage of area above 30°, relief, slope of the main channel and circularity index); while the second (MII) is applied to determine basin susceptibility and the magnitude of the events triggered based on the use of nine morphometric parameters (longitudinal profile, roughness index, relief ratio, relief, melton, percentage of area above 25°, drainage density, drainage confluence and drainage hierarchy). For both methods was used an inventory based on debris flows triggered in 1995 and 2012. The application of MI resulted in the classification of 12% of the basins as Very High susceptibility, 40% as High, 20% as Medium, 20% as Low and 20% as Very Low susceptibility. MII resulted in 14% High Susceptibility basins, 36% Medium, 44% Low and 2% Very Low. Out of the basins classified as Very High and high susceptibility by MI (51%), 42% were affected by debris flows. On the other hand, out of the basins classified as Low susceptibility (20%), 50% were affected by debris flows, which is equivalent to 10% of all basins studied. Out of the basins classified as Very High and High susceptibility by MII (14.6%), 33.3% were affected by debris flow. In addition, from the medium susceptibility basins (36%), there were decries flows in 60% of them. While MI overestimates areas of greatest susceptibility, M2 classifies into the Low Susceptibility class an expressive number of basins which present recorded occurrences. These results can be related to weights and class intervals established by MI and MII, which were not developed to the Serra Geral escarpment context. Despite their limitations, these methods can be recalibrated from a morphometric evaluation of areas already affected by debris flows.