Abstract
Urban floods repeatedly threaten Barcelona, damaging the city infrastructure and endangering the safety of the population. The urban planning of the city, the socioeconomic distribution, its topography, and the characteristics of precipitation systems translate into these flood events having a heterogeneous effect across the city. It means that the coping capacity has a strong dependence on local factors that must be considered when management plans are developed by the municipality. This work aims to contribute to the better knowledge of precipitation structures associated with heavy rainfall events and floods in Barcelona based on radar data and an urban rain gauge network. Radar data have been provided by the Meteorological Service of Catalonia (SMC), while precipitation data, impact data, and early warnings, have been provided by Barcelona Cicle de l’Aigua S.A. (BCASA), for the period 2013–2018. A new radar-based methodology has been developed to identify convective rainfall structures from radar reflectivity volumes (CAPPI and TOP products) to make the analysis easier. The high computing speed of the procedure allows efficient analysis of a large set of convective cells without scarifying temporal resolution of radar data. Both rainfall fields (radar and rain gauge, respectively) have been compared. Then through the identified rainfall convective structures, thunderstorm hotspots have been identified. Considering an alert indicator from BCASA and the reported incidents, episodes with the highest impact have been analysed in depth. Results show 207 significant rainfall episodes in the ROI for the six years, which are mainly concentrated between September and November. The fact that significant episodes are usually produced by highly convective rain corroborates the advantage of using radar images as a tool to detect any maxima even when no rain gauge is there. In 64 of the episodes, the level of pre-alert was achieved with a maximum frequency between August and September. The proposed algorithm shows more than 8000 centroids of convective cells from 189 cases. Whilst maximum surface reflectivity over 45 dBZ is more prone to occur near the coastline, the centroids of storm cells tend to concentrate more inland. The final objective is to improve the actions taken by the organisation responsible for managing urban floods, which have seen Barcelona recognised as a model city for flood resilience by the United Nations.
Highlights
This article is an open access articleHydrometeorological hazards especially affect the Mediterranean basin, where heavy rainfalls play an important role and usually produce flash floods, surface floods and urban floods
A database was created by combining data from the Barcelona Cicle de l’Aigua S.A. (BCASA) rain gauge network and XRAD radar products from April 2013 to December 2018
The methods used were able to identify some areas in the city with a greater concentration of storm centroids than others
Summary
Hydrometeorological hazards especially affect the Mediterranean basin, where heavy rainfalls play an important role and usually produce flash floods, surface floods and urban floods. In Catalonia (NE of the Iberian Peninsula, and NW of the Mediterranean Basin), floods are the most damaging natural hazard [2], distributed under the terms and conditions of the Creative Commons. The Spanish Insurance Compensation Consortium (in Spanish, Consorcio de Compensación de Seguros—CCS) paid out over 450 million euros between 1996 and 2015. Other private insurance expenses must be added. Convective and very localised precipitation is responsible for 70% of the flood episodes along the Catalan coast [6,7], affecting the most densely populated Catalan counties in one out of three cases
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