This work presents a protocol and a model to obtain the sizes of the pebbles in mountain rivers from uncrewed aerial vehicle images. A total of 12 rivers located in southeastern France were photographed to build the model. The results show that the model has little error and should be usable for similar rivers. The grain size of mountain rivers is an important parameter for environmental diagnostics by mapping the aquatic habitats and for flood management by estimating the pebble fluxes during floods.

Snow avalanches pose substantial risks to communities and public safety in Colorado. We studied tree growth patterns impacted by avalanches from 1698 to 2020 alongside meteorological data. We found variations in avalanche frequency revealing a decline in regional avalanche activity and shifts in the causes of these types of large and widespread avalanche events. This knowledge can enhance avalanche safety measures and infrastructure design.

This paper proposes a methodology to develop a long-range multirisk database. Combining scattered pre-existing records and intensive research in historical archives provides a 1600–2020 record of past events in a valley of the French Alps. It goes far beyond any inventory existing in terms of number of events, temporal coverage and detailed description of events characteristics in a mountain context. Spatio-temporal patterns are analysed, opening perspective for multirisk assessment.

We assess projected changes in snowfall extremes in the French Alps as a function of elevation and global warming level for a high-emission scenario. On average, heavy snowfall is projected to decrease below 3000 m and increase above 3600 m, while extreme snowfall is projected to decrease below 2400 m and increase above 3300 m. At elevations in between, an increase is projected until +3 °C of global warming and then a decrease. These results have implications for the management of risks.

Avalanches are a significant issue in mountain areas where they threaten recreationists and human infrastructure. Assessments of avalanche hazards and the related risks are therefore an important challenge for local authorities. Meteorological and snow cover simulations are thus important to support operational forecasting. In this study we combine it with mechanical analysis of snow profiles and find that observed avalanche data improve avalanche activity prediction through statistical methods.