Assessing Climate-Driven Changes in Rainfall-Induced Landslide Probability Using Distributed Hydrological Modeling

Rainfall-induced shallow landslides represent a critical natural hazard in mountainous regions, with their frequency controlled by hydrological processes. Climate change is expected to alter both precipitation patterns and soil moisture dynamics but quantifying these impacts on landslide susceptibility remains challenging.

In this study, we integrate physically-based stability thresholds with distributed hydrological modeling to assess future landslide hazard evolution under multiple climate scenarios. The study is conducted for a small basin (~28 km²) located in the north-eastern Friuli Venezia Giulia (Italy).

Spatially explicit Critical Soil Moisture (CSM) and Critical Wetness Index (CWI) thresholds at 50 m resolution were derived in a previous effort for multiple failure depths (0.75 to 2.00 m) by inverting the infinite slope stability analysis. The thresholds represent hydrological conditions at which slope failure may initiate through either unsaturated zone processes or groundwater table rise. These thresholds were coupled with a calibrated distributed and physically-based hydrological model, the Triangulated Irregular Network‐based real‐time integrated basin simulator (tRIBS), which simulates hourly soil moisture and groundwater dynamics, to assess the occurrence of failure over 100-year periods for three synthetically generated climate scenarios: current conditions, moderate emissions (RCP4.5, 2050), and high emissions (RCP8.5, 2050). The synthetic series of meteorological variables, and particularly precipitation, were generated by combining the AWE-GEN (Advanced WEather GENerator) model with a procedure to correct the distribution of extreme events.

We quantify exceedance frequencies, i.e., the proportion of time during which CSM and CWI thresholds are exceeded, as a measure of temporal exposure to landslide-conducive conditions. Results reveal that, under RCP4.5, exceedance frequencies decrease by up to 14.6% (CWI) and 10.9% (CSM), due to a reduction in annual precipitation despite an increase in mean intensity per event. In contrast, RCP8.5 shows bidirectional patterns, with maximum increases reaching 5.1% (CWI) and 3.6% (CSM), indicating that precipitation intensification begins to overcome the reduction in annual precipitation. Critically, climate impacts amplify with failure depth; the 2.00 m failure depth exhibits changes in magnitude up to three times greater than those at 0.75 m, suggesting that deeper failures become disproportionately more sensitive to climate change.

This research received funding from European Union NextGenerationEU – National Recovery and Resilience Plan (PNRR), Mission 4, Component 2, Investment 1.1 -PRIN 2022 – 2022ZC2522 - CUP G53D23001400006.