Monitoring the role of soil hydrologic conditions and rainfall for the triggering of torrential flows in the Rebaixader catchment (Central Pyrenees, Spain)

Abstract

Torrential flows (debris flows and debris floods) are mainly triggered by precipitation and soil hydrological processes. Most early warning systems in torrential catchments are rainfall-based. However, this approach can result in frequent false positives, due to its pure black-box nature, in which soil water conditions are neglected. We aim to contribute to the understanding of the conditions required for triggering torrential flows by considering also in situ measurements of soil water content. Herein, monitoring data of 12 years of rainfall and torrential flow occurrence (2009–2020) and 8 years of soil hydrologic conditions (2013–2020) in the Rebaixader catchment (Central Pyrenees, Spain) are analyzed. The dataset includes more than 1000 rainfall events and 37 torrential flows. First, rainfall thresholds using maximum rainfall intensity (Imax) and mean intensity (Imean) are defined. For the 2013–2020 dataset, which includes 15 torrential events, the Imean threshold predicted 2 false negatives and 73 false positives (positive predictive value, PPV, of 15.1%) and the best Imax threshold predicted also 2 false negatives but only 11 false positives (PPV of 54.2%). However, our observations confirmed quantitatively that the lower is the soil moisture the higher is the rainfall intensity to trigger torrential flows. Then, we combined Imax and volumetric water content at 15 and 30 cm depth to define a hydro-meteorological threshold. This latter threshold reduced false negatives to 1 and false positives to 8 and increased the PPV to 63.6%. These results confirm that soil hydrological conditions are key factors for torrential flow triggering and may improve early-warning predictions.

Recent advancements of landslide hydrology

“…On the other hand, the simulation-based forecast model performed worse than the At a smaller scale of analysis (i.e., catchment or local/slope), the incorporation of antecedent hydrological information, either by field measurements or by hydrological modeling (Mostbauer et al, 2018;Prenner et al, 2018Prenner et al, , 2019 is useful for landslide prediction. Inclusion of hydrometeorological information helps in understanding the different triggering processes of debris flows in alpine catchments in Austria (Mostbauer et al, 2018;Prenner et al, 2018Prenner et al, , 2019 and in the Pyrenees (Oorthuis et al, 2023). Measurements of antecedent soil wetness, coupled with physically based modeling, allow identifying reliable rainfall thresholds for landslide triggering (e.g., Abraham, Satyam, Bulzinetti, et al, 2020;Wei et al, 2020), in some cases leading to the definition of different thresholds for wet and dry soil conditions (e.g., De Vita et al, 2018;Napolitano et al, 2016).…”

The Role of Water and Weathering Processes in Landslides in Hungarian Loess Sediments

“…However, these bluffs are unstable, and mass movements are frequent. One of the reasons for mass movements is the special hydrological properties of these areas [1]. The river water level, the ground water, rain, and the domestic water together affect the physical and chemical properties of the soil in these areas.…”

“…This is a key issue both from the economic and safety points of view. In this research, the following were studied: (1) the relation between the water level of the Danube (1960-2020), the amount of rainfall , and dates of mass movements from 1960-2014 in Kulcs; (2) changes in the mineral composition of loess and loessy sediments during dry, wet, and flood periods; and (3) human influence on the occurrence of landslides.…”

Regional-scale analysis of weather-related rockfall triggering mechanisms in Norway, and its sensitivity to climate change

“…For the case of shallow landslides and debris flows regional-scale early warning systems have been widely adopted to predict occurrence of future landslide events (NOAA-USGS Debris Flow Task Force 2005; Kirschbaum and Stanley 2018;Segoni et al 2018;Park et al 2019;Palau et al 2020). Such systems generally employ rainfall thresholds to distinguish between the weather conditions prone to triggering landslides and those that are not (Caine 1980;Guzzetti et al 2008;Abancó et al 2016;Gariano et al 2020;Oorthuis et al 2023).…”