Soil moisture information can improve shallow landslide forecasting using the hydrometeorological threshold approach
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Pasquale Marino I David J. Peres I Antonino Cancelliere I Roberto Greco I Thom A. Bogaard
Soil moisture information can improve shallow landslide forecasting using the hydrometeorological threshold approach
Abstract Empirical thresholds indicating the meteorological conditions leading to shallow landslide triggering are one of the most important components of landslide early warning systems (LEWS). Thresholds have been determined for many parts of the globe and present significant margins of improvement, especially for the high number of false alarms they produce. The use of soil moisture information to define hydro-meteorological thresholds is a potential way of improvement. Such information is becoming increasingly available from remote sensing and sensor networks, but to date, there is a lack of studies that quantify the possible improvement of the performance of LEWS. In this study, we investigate this issue by modelling the response of slopes to precipitations, introducing also the possible influence of uncertainty in soil moisture provided by either field sensors or remote sensing, and investigating various soil depths at which the information may be available. Results show that soil moisture information introduced within hydro-meteorological thresholds can significantly reduce the false alarm ratio of LEWS, while keeping at least unvaried the number of missed alarms. The degree of improvement is particularly significant in the case of soils with small water storage capacity. Keywords Shallow landslide . Rainfall-induced landslide . Early warning system . Hydrological cause . Triggering rainfall event . Hydro-meteorological thresholds . Landslide hazard and risk management Introduction Forecasting rainfall-induced landslides is often entrusted to the definition of empirical thresholds (usually expressed in terms of rainfall intensity and duration) that link the precipitation to the triggering of landslides (Guzzetti et al. 2008). However, rainfall intensity-duration thresholds do not exploit the knowledge of hydrological processes that occur in the slope, so they tend to generate significant rates of false and missed alarms, reducing the credibility of landslide early warning systems (LEWS). Rainfallinduced shallow landslides usually occur in the initially unsaturated soil cover following an increase of pore water pressure, due to the increase of soil moisture, caused by large and persistent rainfall. So, this opens the possibility to use soil moisture in landslide research. Recently, Bogaard and Greco 2018 proposed the cause-trigger conceptual framework to develop hydrometeorological thresholds that combine the antecedent causal factors and the actual trigger connected with landslide initiation. In fact, in some regions where rainfall-induced shallow landslides are particularly dangerous and pose a serious risk to people and infrastructures, the antecedent saturation is the predisposing factor, while the actual landslide triggering is associated with the hydrological response to the recent and incoming prec
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