Hydrometeorological controls and social response for the 22 October 2019 catastrophic flash flood in Catalonia, north-eastern Spain

Abstract. On 22 October 2019, the Francolí river basin in Catalonia, north-eastern Spain, experienced a heavy precipitation event that resulted in a catastrophic flash flood, causing six fatalities. Firstly, this study investigates the hydrometeorological factors that concurred in the unfolding of this event by using large-scale meteorological grid analyses, high-resolution mesoscale model simulations, radar-derived precipitation estimates, post-flood field observations and hydrological modelling. Mesoscale diagnosis reveals that a persistent south-easterly airflow brought low level moisture and established convective instability over the region, while local orography was instrumental to trigger moist deep convection. A convective train promoted intense, copious and prolonged precipitation over the north-western catchment headwaters. Basin response was significantly modulated by the very dry initial soil moisture conditions. After the long-lasting rainfall, an acute burst of precipitation resulted in extreme flash flooding. Fast and abrupt increases in river flow lead to short times for protection procedures to be implemented effectively. Secondly, this study collects the social response times during the event and compares them with catchment dynamics. The idea is to examine the adequacy of monitoring and warning issuance in meeting the needs of the population at risk. Based on this information, the study provides recommendations aimed at minimizing losses and improving preparedness for similar natural hazards in the future.