Empirical rainfall thresholds for the triggering of landslides in northern Portugal and Spain: a preliminary overview
- 1Department of Earth Sciences and Condensed Matter Physics, Universidad de Cantabria.
- 2Centre for Geographical Studies, Institute of Geography and Spatial Planning, Universidade de Lisboa.
- 3Department of Geology, Universidad de Oviedo.
- 4Department of Geography, Urban and Regional Planning, Universidad de Cantabria.
- 5Department of Geology, University of the Basque Country (UPV/EHU).
- 6Department of Geographical Engineering and Graphic Expression Techniques, Universidad de Cantabria.
Landslides, common and widespread phenomena in the north of the Iberian Peninsula, represent a relevant cause of geomorphological hazard, in particular in some mountainous and densely populated areas of Portugal and Spain. Rainfall is the most relevant landslide-triggering factor in these territories within the Iberian Atlantic Arc, characterized by an Oceanic climate with some areas of Mediterranean influence and average annual precipitation in the range 900-1900 mm.
Since the 1980s, several research groups have been developing work lines focused on the study of the temporal occurrence of landslides and its relationship with different precipitation patterns by calculating empirical rainfall thresholds. Their computation is mainly based on the statistical analysis of individual or multiple rainfall events which caused landslides in the past. A wide variety of approaches considering different data sets, methodologies and spatio-temporal scales have been conducted. However, some results have not been greatly disseminated or have remained unpublished, hampering the overall analysis of research carried out up to date.
The present work aims to review the literature related to empirical rainfall thresholds in the north and northwest of the Iberian Peninsula with the objectives of (i) synthesizing existing data, (ii) establishing comparison criteria that consider the different characteristics of each study area, data set, and methodology used, and (iii) addressing a joint analysis. The study zones are located the north of Portugal (Oporto, Vila Real-Douro Valley and Casal Soeiro areas) and in the north of Spain (Asturias, Cantabria and Guipuzcoa and Vizcaya provinces within the Basque Country).
The review revealed that over 80 landslide rainfall thresholds have been compiled, most of them defined through equations. To describe the critical rainfall-triggering conditions, 75% of the thresholds considered the accumulated precipitation during a specific period, while the remaining 25% considered the precipitation intensity. Critical accumulated rainfall in 24 hours showed appreciable variations in the range 20-140 mm in Spain and 20-80 mm in Portugal. Almost 70% of the thresholds showed regional representativeness; the remaining rest showed local representativeness.
How to cite: Valenzuela, P., Vaz, T., Domínguez-Cuesta, M. J., Pereira, S., Zêzere, J. L., Rivas, V., Remondo, J., Bonachea, J., González-Díez, A., Bornaetxea, T., Sánchez-Espeso, J., San Millán, E., and Francos, L.: Empirical rainfall thresholds for the triggering of landslides in northern Portugal and Spain: a preliminary overview, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-143, https://doi.org/10.5194/icg2022-143, 2022.
