Supercells and large hail in Spain

Supercell storms are often associated with severe-weather phenomena such as heavy rainfall, hail, tornados or straight-line winds (downbursts or derechos), all of which can have impactful socio-economic and environmental consequences. Despite these impacts, the lack of data of supercell storms has limited their analysis and characterization of the climatology across Spain. This constraint has been addressed through a voluntary, collaborative effort to create a database of supercell events from January 2011 to December 2021. During the 11-year study period, 2,087 storms with supercell characteristics were identified. Citizen collaboration confirmed 13.7 % of the supercells detected in PPI radar images. The database also includes hail size and/or tornadoes associated with each supercell whenever such information was reported. The results reveal a spatial distribution with high supercell activity in eastern Spain, mainly in Mediterranean areas and the north-eastern part of the Iberian Peninsula.

From 2022 onward, only supercells with high socio-economic impact - specifically, those accompanied by large hail (≥ 5 cm) - have been compiled. In addition, a thorough review of the national newspaper archive is under way to identify and catalogue large-hail events from 2000 to the present. Because photographs to determine hail size are often unavailable, a proxy based on the damage reported in the press has been developed to identify these events. Currently, more than 240 large-hail events have been catalogued in Spain (Peninsula and Balearic Islands) for 2000-2024. Among them, 44 events reported very large hail (≥ 7 cm) and 7 involved giant hail (≥ 10 cm), three of which occurred in the last three years. The convective environments show substantial differences in the different large-hail categories. The trend shows a significant increase in both the number of days with hail and the number of hail events in Spain.