Rain-on-snow events, floods and climate change in the Alps: Events may increase with warming up to 4°C and decrease...

Area of Science:

• Climatology
• Hydrology
• Environmental Science

Background:

• Mountain rain-on-snow (ROS) events are significant drivers of major floods in alpine catchments.
• Assessing the historical evolution and future changes of ROS events is crucial for understanding flood risk under climate change.

Purpose of the Study:

• To analyze the trend of ROS events in a Swiss alpine catchment over recent decades.
• To project potential changes in ROS event frequency and associated flood risks in a changing climate.

Main Methods:

• Utilized historical climate and hydrological data from the Sitter catchment in north-eastern Switzerland.
• Employed a simple temperature-based snow model to simulate ROS event evolution under varying temperature scenarios.

Main Results:

• Observed a notable increase in the frequency of ROS events since the early 1960s, correlated with rising atmospheric temperatures.
• Model simulations indicate a potential 50% increase in ROS events with 2-4°C warming, followed by a decline at higher warming levels.

Conclusions:

• The frequency of mountain rain-on-snow events has increased, contributing to heightened flood risks.
• Future climate change is projected to intensify flood risks in alpine areas due to more frequent ROS events, at least initially.