Study of Extreme Flash Flood Events in Mediterranean Spain

Flash floods represent the most devastating natural hazard in Mediterranean Spain, resulting in significant fatalities and economic losses. Their characterization has been hindered by the absence of a comprehensive database. This study addresses this challenge by compiling and analyzing data using established methodologies. The analysis is structured into two parts. The first part explores extreme daily rainfall patterns in Mediterranean and semi-arid climatic zones during the extended warm season. It utilizes data from 99 flash floods to investigate spatial and temporal distributions and derive envelope curves. The findings reveal that the spatial and temporal patterns of extreme flash floods closely align with those of extreme daily precipitation. The envelope curves are consistent with other regions. In the semi-arid region, flash floods exhibit higher magnitudes, but its envelope curve declines more steeply with increasing drainage size, reflecting distinct climatic and physiographic factors. The second part examines 13 major flash flood events using high-resolution hydrometeorological data. These events are characterized based on climate, basin morphology, precipitation, runoff ratio, lag time, and flashiness. The results confirm previous observations regarding relief ratio, rainfall intensity, and flashiness. However, runoff coefficients are lower than those in other European regions due to the high initial soil storage capacity, which prolongs lag times in smaller basins. In larger basins, flow hydraulics lead to reduced lag times that fall below the lower limit of the European envelope curve. These findings contribute to the expansion of the European flash flood database and provide insights for enhancing flood risk management strategies in Mediterranean Spain.