Dear Colleagues,

Rainfall is the most important physical process for landslide triggering worldwide. However, the relationship between rainfall and landslides is indirect and typically includes a process cascade in which the rainfall is followed by infiltration into the soil, which increases the pore-water pressure that is responsible for the decrease in the shear strength of the slope materials. Moreover, the control of rainfall on landslides differs substantially depending upon landslide depth and kinematics and the affected material. Therefore, the critical rainfall conditions for failure are not the same for different types of landslides and may be strongly influenced by regional geologic and geomorphologic conditions.

During the last few decades, the relationship between landslides and rainfall has been tentatively established using physical and empirical approaches to assess rainfall thresholds, i.e., rainfall conditions (cumulated rainfall, intensity), that when reached or exceeded can induce a landslide event. The physical approach considers the physical basis of the process using hydrological models and stability calculations, which demand high-resolution data (e.g., groundwater conditions, shear strength properties). The empirical approach is statistically based and is sustained by historical records regarding landslide events and rainfall data series.

Rainfall thresholds are crucial for the implementation of landslide early warning systems (EWS) aimed at reducing the number of deaths and affected people as well as the frequent destruction of assets and disruption of economic and social activities due to landslides. Disaster risk tends to increase as a consequence of global changes in societal structures, rapid urbanization, growing exposure of population and assets, and climate change. To cope with this, early warning systems (EWS) for disaster risk reduction (DRR) were considered a powerful tool by the Sendai Framework for Disaster Risk Reduction 2015–2030.

This Special Issue of Water discusses concepts, methods, and techniques to assess hazards and risks associated with rainfall-triggered landslides.

Topics of interest include (but are not limited to) the following:

• Assessment and validation of rainfall thresholds for landslide occurrence
• Comparison and extrapolation of rainfall thresholds
• The magnitude-frequency of rainfall-triggered landslide events
• The implementation of EWS for landslides

Prof. Dr. José Luís Zêzere
Guest Editor

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• rainfall thresholds
• magnitude-frequency
• landslide hazard
• landslide risk
• early warning systems