Abstract
AbstractThe Mediterranean region is frequently affected by heavy precipitation episodes and subsequent flash flooding. An exemplary case is the heavy precipitation episode that occurred in the regions of València, Murcia, and Almería (eastern Spain) on 12 and 13 September 2019. Observed rainfall amounts were close to 500 mm in 48 h, causing seven fatalities and estimated economical losses above EUR 425 million. This case exemplifies the challenging aspects of convective-scale forecasting in the Mediterranean region, with kilometer-resolution meteorological fields required over long forecast spans. Understanding the key mesoscale factors acting on the triggering, location, and intensity of the convective systems responsible for extreme accumulations is essential to gain insight into these episodes and contribute toward their accurate hydrometeorological forecasting. Mesoscale diagnosis suggests that local and distant orography, together with air–sea fluxes, were instrumental in developing convection and intensifying precipitation rate. Sensitivity experiments confirm the role of orography in organizing the cyclonic flow over the southeast part of the western Mediterranean, and also acting as a convection-triggering mechanism. Furthermore, results highlight the role of latent heat flux from the Mediterranean Sea in enhancing convective instability at lower levels and moistening the environment. These moist feeding flows substantially contribute to increasing precipitation rates. Such high sensitivity to environmental moisture distribution naturally propagates to the sea surface temperature, which, by means of sensible and latent heat flux exchanges, dominated the evolution of convective activity for the 12–13 September 2019 episode.
Highlights
Flash floods are among the most devastating natural hazards
The confluence of a northeasterly and an easterly low-level jets advected high ue air over this area, feeding the thin convective band which developed over Cap de la Nau as well as the subsequent linear structure developed during phase 2
The high resolution required to produce accurate quantitative precipitation forecasts severely restricts the predictability horizon of convection and subsequent flash flooding. This fact combined with the long time span of this episode makes precise QPF extremely challenging
Summary
Flash floods are among the most devastating natural hazards. They are responsible for high socioeconomic impacts, including human casualties and property loss and damage. The western Mediterranean littoral is characterized by the presence of steep small catchments that favor the development of flash floods. Coastal regions in northwestern Italy (e.g., Buzzi et al 1998; Turato et al 2004; Fiori et al 2014), southeastern France (e.g., Sénési et al 1996; Delrieu et al 2005; Nuissier et al 2008), and eastern Spain (e.g., Homar et al 1999, 2002; García-Herrera et al 2005) are flash flood–prone areas. The eastern coast of Spain is a remarkable example of a Mediterranean region persistently affected by heavy precipitation episodes (HPEs) resulting in flash flooding. Some historical examples are the episodes of 3 November 1987 in Gandia (València, eastern Spain) with 800 mm in 24 h (Llasat and Puigcerver 1994), 10 October 1994 with 400 mm in 24 h (Ramis et al 1998), or 12 October 2007 with 400 mm in 24 h (Pastor et al 2010)
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