Abstract
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 (1979–2010), 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.
Highlights
Flash floods in arid mountainous regions are destructive natural disasters
Many challenges exist for the development and use of an early warning system (EWS) for flash floods in a hyper-arid catchment
An early warning system (EWS) for flash floods has been developed for part of the Sinai peninsula of Egypt, an hyperarid 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
Summary
Flash floods in arid mountainous regions are destructive natural disasters. A flash flood can be generated instantly during or shortly after a rainfall event, especially when highintensity rain falls on steep hill slopes with exposed rocks and lack of vegetation (Lin, 1999; Wheather, 2002). The most important processes in arid catchments are: infiltration, routing and transmission losses as described e.g. by Pilgrim et al (1988), Gheith and Sultan (2002), Foody et al (2004), Morin (2006) and Bahat et al (2009). Many arid catchments have impermeable hill slopes and highly permeable alluvial channel beds through which floodwater infiltrates.
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