Abstract. An early warning system (EWS) for flash floods has been developed for part of the Sinai peninsula of Egypt, an hyper-arid area confronted with limited availability of field data, limited understanding of the response of the wadi to rainfall, and a lack of correspondence between rainfall data and observed flash flood events. This paper shows that an EWS is not a "mission impossible" when confronted with large technical and scientific uncertainties and limited data availability. Firstly, the EWS has been developed and tested based on the best available information, this being quantitative data (field measurements, simulations and remote sensing images) complemented with qualitative "expert opinion" and local stakeholders' knowledge. Secondly, a set of essential parameters has been identified to be estimated or measured under data-poor conditions. These are: (1) an inventory of past significant rainfall and flash flood events, (2) the spatial and temporal distribution of the rainfall events and (3) transmission and infiltration losses and (4) thresholds for issuing warnings. Over a period of 30 yr , only 20 significant rain events have been measured. Nine of these resulted in a flash flood. Five flash floods were caused by regional storms and four by local convective storms. The results for the 2010 flash flood show that 90 % of the total rainfall volume was lost to infiltration and transmission losses. Finally, it is discussed that the effectiveness of an EWS is only partially determined by technological performance. A strong institutional capacity is equally important, especially skilled staff to operate and maintain the system and clear communication pathways and emergency procedures in case of an upcoming disaster.

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This paper details the methodology which is used to perform a flood risk analysis for the Belgian coast. The coastal flood risk analysis aims at estimating the expected value of yearly consequences by coastal flooding for a given time horizon. To calculate the risk all sources of uncertainty are accounted for by using a pragmatic probabilistic method. To calculate the flood consequences for a given extreme storm surge, a chain of process models is used that describe the wave propagation towards the coast, the failure behaviour of the coastal defences, the flooding of the coastal plain and the resulting consequences (economic damage and human casualties).

The Flash Flood Manager project (acronym "FlaFloM, co-funded by the EU under the LIFE Third Countries Fund) is aimed at developing an early warning system for forecasting flash floods in the Wadi Watier catchment, located in the Sinai Peninsula (Egypt). The system consists of a number of components, which are automatically activated and linked: a rainfall forecasting model (Weather Research and Forecast model), a hydrological model (custom-built to reflect arid region conditions), a hydraulic model (InfoWorks-RS) and a warning module (FloodWorks). Forecasts have a lead time of up to 48 hours. The system is currently in an operational testing phase. This paper provides a brief overview of the early warning system and addresses a number of challenges related to the development and calibration of the hydraulic model, as well as the definition of threshold levels in the warning module.

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