HS4.1.3/NH1.32HS4.1.3/ NH1.32

Flash floods and associated hydro-geomorphic processes: observation, modelling and warning (co-organized) 
Convener: Olivier Payrastre  | Co-conveners: Isabelle Braud , Jonathan Gourley , Marcel Hürlimann , Massimiliano Zappa 
Intense rainfall and/or orographic precipitation events in small and medium size catchments can trigger flash floods, which are characterized by very short response times and high specific peak discharges. Under appropriate topographic conditions, such rainstorms also cause debris flows or shallow landslides mobilizing large amounts of unconsolidated material. Although significant progress has been made in the last decade in the management of flash floods related risks, these events remain poorly understood and their predictability is limited by a high non-linearity in the hydrological response, related to threshold effects and structured heterogeneity at all scales. In addition, predicting the initiation and runout of rainfall-induced landslides and their interactions with hydrological and hydraulic processes is still affected by large uncertainties. Therefore, improving the flash floods understanding, forecasting and risk management capacities requires multi-disciplinary approaches, as well as innovative measurements and modelling approaches as these events often occur in ungauged basins.

This session welcomes contributions illustrating current advances and approaches in monitoring, modelling, forecasting and warning flash floods and associated geomorphic processes. Contributions documenting the societal responses and impacts, and analysing risk management systems are also welcome. The session will cover the following main scientific themes:
- Development of new measurement techniques adapted to flash floods monitoring and quantification of the associated uncertainties
- Use of remote sensing data, weather radar, and lightning for improving forecasting models input data
- Development of modelling tools for predicting and forecasting flash floods and/or rainfall-induced landslides in gauged and ungauged basins
- Use of new criteria such as specific “hydrological signatures” for model and forecast evaluation
- Identification of processes leading to flash flood events and/or rainfall-induced landslides from data analysis and/or modelling, and of their characteristic space-time scales
- Evolutions in flash-flood characteristics possibly related to changing climate.
- Observation, understanding and prediction of the social vulnerability and social response to flash floods and/or associated landsliding
- Flash flood and/or rainfall-induced landslide risk assessment using multi-disciplinary approaches and warning systems, and evaluation of the relevance of those systems.