Empirical rainfall thresholds for landslide activity based on long-term Portuguese meteorological stations

In this research the occurrence of landslides triggered by rainfall is investigated through the assessment of rainfall thresholds for three regions in Portugal: Lisbon, Oporto, and Coimbra. An historical landslide inventory is used, based on newspapers published between 1865 and 2010, associated with daily precipitation databases from three long-term meteorological stations. An empirical approach based on antecedent rainfall is applied to define the rainfall thresholds for landslides occurrence. The analysis is focused on each single rain gauge, for which the spatial representativeness is evaluated. The daily rainfall data is analysed using the Gumbel probability distribution for different durations. The critical rainfall combinations (cumulated rainfall duration) with the highest return period are associated with the landslide occurrence.

For the three regions, rainfall thresholds are defined from regression (linear and potential), extreme values (upper and lower) and probability (probability of a rainfall event resulting in a landslide event when the threshold is exceeded), and the results are assessed and calibrated using the receiver operating characteristic (ROC) metrics. The thresholds comparation reveal regional patterns in rainfall thresholds. The differences in regional critical rainfall conditions for landslide occurrence between regions are associated with geological, geomorphological, and climatic features.

 

This work is part of the project BeSafeSlide (BSS) - Landslide Early Warning soft technology prototype to improve community resilience and adaptation to environmental change [PTDC/GES-AMB/30052/2017]. JL Zêzere was supported by the RiskCoast project - Development of tools to prevent and manage geological risks on the coast linked to climate change, Interreg SUDOE [SOE3/P4/EO868]