S2

Floods: Processes, Forecasts, Probabilities, Impact Assessments and Management
Convener: Svenja Fischer | Co-Conveners: Andreas Schumann, Günter Blöschl, Elena Volpi, Christopher White, Alberto Viglione, Marcelo Uriburu

One main aspect of the direct socio-economic relevance of hydrology consists in its ability to predict or to forecast extreme flood events. Prediction refers here to the assessment of the probability of a value related to the flood (e.g., the maximum peak discharge during one event) to be exceeded, without specifying the time of occurrence. Forecast refers instead to a statement of the future development of a variable related to the flood with a specification of the time of occurrence. With regard to their impacts, floods play a very important role for the society in general and human beings living in flood prone areas in particular. Because of missing information and a short memory of harmful events in the past, the public awareness of floods is often insufficient and flood prevention and protection are insufficient in many parts of the world. Existing tools and methods for flood prediction and forecast may be outdated, as new problems have to be considered, e.g. such as:
• increased uncertainties, caused by climate change and human impacts;
• first indicators for changing flood regimes, caused by climate variabilities;
• relevance of interlinks between atmosphere and river basins in the formation of extreme floods;
• risks as a result of the concentration of people and goods in river valleys;
• demand for more reliable hydrological data for flood design;
• complexity of flood protection at the river basin scale, where one human intervention may affect the impacts of existing or planned measures in not foreseeable ways several others, and so on.
It is explicitly encouraged to link to the Unsolved Problems in Hydrology (UPH) Initiative (https://iahs.info/IAHS-UPH.do), which includes (but is not exclusive)
1. Is the hydrological cycle regionally accelerating/decelerating under climate and environmental change, and are there tipping points (irreversible changes)?
9. How do flood-rich and drought-rich periods arise, are they changing, and if so why?
10. Why are runoff extremes in some catchments more sensitive to land-use/cover and geomorphic change than in others?
11. Why, how and when do rain-on-snow events produce exceptional runoff?
19. How can hydrological models be adapted to be able to extrapolate to changing conditions, including changing vegetation dynamics?
20. How can we disentangle and reduce model structural/parameter/input uncertainty in hydrological prediction?
The large variety of flood problems demand collaborative actions of experts from different branches of hydrology. Therefore, this call covers many aspects related to floods, including processes of flood generation, the assessments of flood probabilities, regionalization issues, flood forecasting and the need for impact forecasts and other economic aspects of risk management.