Articles | Volume 373
12 May 2016
 | 12 May 2016

Small-scale (flash) flood early warning in the light of operational requirements: opportunities and limits with regard to user demands, driving data, and hydrologic modeling techniques

Andy Philipp, Florian Kerl, Uwe Büttner, Christine Metzkes, Thomas Singer, Michael Wagner, and Niels Schütze

Abstract. In recent years, the Free State of Saxony (Eastern Germany) was repeatedly hit by both extensive riverine flooding, as well as flash flood events, emerging foremost from convective heavy rainfall. Especially after a couple of small-scale, yet disastrous events in 2010, preconditions, drivers, and methods for deriving flash flood related early warning products are investigated. This is to clarify the feasibility and the limits of envisaged early warning procedures for small catchments, hit by flashy heavy rain events. Early warning about potentially flash flood prone situations (i.e., with a suitable lead time with regard to required reaction-time needs of the stakeholders involved in flood risk management) needs to take into account not only hydrological, but also meteorological, as well as communication issues. Therefore, we propose a threefold methodology to identify potential benefits and limitations in a real-world warning/reaction context. First, the user demands (with respect to desired/required warning products, preparation times, etc.) are investigated. Second, focusing on small catchments of some hundred square kilometers, two quantitative precipitation forecasts are verified. Third, considering the user needs, as well as the input parameter uncertainty (i.e., foremost emerging from an uncertain QPF), a feasible, yet robust hydrological modeling approach is proposed on the basis of pilot studies, employing deterministic, data-driven, and simple scoring methods.

Short summary
The paper identifies the opportunities and limits of flood early warning in small catchments. Flood early warning for small, fast-responding catchments usually need to include rainfall forecasts. First, the demands of potential users of warning products are assessed. Second, the quality and limitations of rainfall forecasts (emerging from meteorological forecasting uncertainty) are investigated. Third, different flood forecasting techniques are compared.