Sub-Hourly Precipitation Extremes in Mainland Portugal and Their Driving Mechanisms

Abstract

Sub-hourly heavy precipitation events (SHHPs) frequently underlie major meteorological hazards, but their comprehensive analysis is still lacking in Portugal. A 71-weather-station dataset for 2000–2020 is used in this article to (1) diagnose SHHPs corresponding to a 10-min precipitation event of at least 5.0 mm, (2) characterize their spatial-temporal distribution, and (3) identify their associated synoptic-scale conditions. Two synoptic types are associated with SHHPs: remote (RemL) and regional (RegL) low-pressure systems. RegL SHHPs display two marked maxima in spring and autumn, while RemL SHHPs show a single maximum in autumn. Most RegL events occur in the afternoon/evening, while RemL events show a slight bias toward midday occurrences. In the case of RemL, the wind is stronger for 2 to 3 h before and during SHHPs, veers from 180° to 210° near the event, the pressure decreases until 20 min before the event, and the wet-bulb temperature decreases around the time of the event and remains low, thus reflecting cold-front passages. For RegL, maximum winds coincide with precipitation peaks, and the wet-bulb temperature briefly decreases in association with downdrafts. A preliminary relationship between the SHHPs and mesoscale convective systems is established by detecting sudden surface-pressure surges, which are indicative of mesohighs caused by evaporatively cooled downdrafts. A calendar of mesohigh episodes linked to SHHPs is provided herein and their signatures are illustrated for the “Pedrógão-Grande” fires. Indicators of several downbursts, cold pools, and mesohighs were identified by the AROME forecast. This first, systematized analysis paves the way to identifying dynamic precursors, enabling their integration into early warning systems and climate projections.

Climate regulation ecosystem services and biodiversity conservation are enhanced differently by climate- and fire-smart landscape management

“…The climate is predominantly Mediterranean, characterized by dry-warm summers (July-September) and cool-wet winters (January-March; Deitch et al 2017). Mean annual total precipitation varies annually from 200-300 to more than 1200 mm (Deitch et al 2017, Santos andBelo-Pereira 2022).…”

Climate- and Fire-Smart Landscape Scenarios Call for Redesigning Protection Regimes to Achieve Multiple Management Goals

“…Climate is mostly Mediterranean with dry-warm summers and wet winters. Mean annual precipitation varies from 500 to 1200 mm following an altitudinal gradient and presents a strong seasonality (Deitch et al, 2017;Santos and Belo-Pereira, 2022). Land cover is mainly shrubland, farmland, and forests (Azevedo, 2012;Sil et al, 2017).…”

Dynamic and Thermodynamic Drivers of Severe Sub-Hourly Precipitation Events in Mainland Portugal

“…The impact of severe precipitation events can be particularly severe in urban areas, causing flash floods and flooding and endangering many lives and properties. These events, and, in particular, short-duration (sub-hourly) events, are commonly caused by deep convective storms [1,[8][9][10][11][12] that are meso-gamma (2-20 km) systems. Although most of the operational numerical weather prediction (NWP) models at the National Weather Centres typically run at a grid spacing of 2 to 15 km, the effective resolution of these models can be 6-10 times the grid spacing [13].…”

“…Climatologically, the spatial distribution of precipitation over mainland Portugal is strongly affected by terrain characteristics [16,17], mainly in the northwestern Atlantic-facing region, where annual average totals exceed 2000 mm, decreasing southeastwards, reaching annual precipitation values that do not exceed 400 mm. In addition to the strong spatial gradients in the mean climate values, precipitation in Portugal is also highly seasonal, with a strong contrast between the dry season (roughly the summer half of the year), with average monthly precipitation values typically not exceeding 20 mm, and the winter wet season, with average monthly precipitation values greater than 100 mm [10]. These are typical features of temperate warm Mediterranean-type climates (the Csa and Csb types in the Köppen-Geiger classification) [18].…”

“…Most studies on severe precipitation events in Portugal have been based on monthly or daily timescales (e.g., [25,26]). Recently, Santos and Belo Pereira [10] analysed subhourly heavy precipitation (SHHP) events in mainland Portugal for the period from 2000 to 2020. This analysis revealed that two main synoptic-scale weather types generate these events.…”