Exploring dynamic and thermodynamic drivers associated with heavy sub-hourly precipitation events in Portugal

This study investigates the dynamics and thermodynamics driving sub-hourly heavy precipitation events (SHHPs) associated with Regional Low-pressure (RegL) systems in mainland Portugal. SHHPs are significant natural hazards, impacting various sectors such as agriculture, particularly viticulture. Using observations from automated surface weather stations from the Portuguese Weather Service (IPMA) from 2000 to 2022, with a 10-minute temporal resolution, this research focuses on three representative stations across different climatic regions. Viana do Castelo station represents the northernmost region, known for high precipitation and strong Atlantic influence. Castelo Branco station, in the central region, is less exposed to Atlantic systems and more influenced by convective systems from western Spain. Faro station, in the south, experiences less influence from maritime polar air masses and more from maritime tropical air masses or Mediterranean/North African systems. The southern region of Portugal demonstrates higher precipitation variability, characterized by intense events occurring on fewer rainy days. The study establishes a link between SHHPs and low-pressure systems west of the Iberian Peninsula (IP). These systems exhibit a cold core, particularly evident at mid-levels, and feature a positive vorticity anomaly extending from the upper troposphere to lower levels. This configuration induces differential positive vorticity advection, especially increasing with height, developing upward motion east of the low-pressure systems over western Iberia. Moreover, these systems facilitate moisture advection over western Iberia at lower levels, evident in positive anomalies of 2-meter dew point temperatures, and promote instability conditions, as diagnosed by various instability indices. Additionally, higher values of total column cloud ice water during heavier precipitation events suggest its potential as a predictor for such occurrences. The study also suggests a potential association of some SHHPs with cut-off lows, though this hypothesis requires further validation. Overall, this research provides a systematic assessment of atmospheric conditions driving SHHPs, contributing to a better understanding of these hazardous events in mainland Portugal.

Acknowledgments: Research funded by National Funds by FCT – Portuguese Foundation for Science and Technology, under the project UIDB/04033/2020 and LA/P/0126/2020 (https://doi.org/10.54499/UIDB/04033/2020). Vine & Wine Portugal—Driving Sustainable Growth Through Smart Innovation, PRR & NextGeneration EU, Agendas Mobilizadoras para a Reindustrialização, Contract Nb. C644866286-011.