Causes and impacts of flash floods: case of Gabes City, Southern Tunisia

Abstract

Flash floods are among the most severe natural hazards that cause disastrous environmental and human impacts. The city of Gabes (Southern Tunisia) is prone to harmful flooding, because of its location on a low plane and its extremely erratic rainfall distribution. Flood risk associated with this is expected to increase further in the coming years due to the high rate of urbanization and an ever growing population. A particular interest is given to a major flooding event, which is the single event that hit the region in the summer season over the last century. Statistical tools, satellite images treatment and analysis, meteorological observation data, Geographic Information System (GIS), and survey data were considered in order to understand and explore the different causes of this disaster, its extent and its consequences. ERA5 is a new global reanalysis tool which was used in this study to evaluate spatial and temporal extent of the examined major rainfall event. A survey was also conducted with 108 participants from different areas of the city. This latter revealed a variety of causes which amplified the flood disaster. The results obtained showed that the flood risk depends not only on rainfall intensity and the event total duration but also on land use, urban development, oasis destruction, and other anthropogenic settings. In this study, procedures are developed to classify and rank the causes and the impacts from the least to the most severe, with special attention to certain problematic spots in the city that were analyzed in detail. Flooding extent areas were estimated and were shown to be in good agreement with the observation data. Recommendations and scenarios to mitigate flood risk are also provided.