Abstract
The large number of floods and landslides that occurred on 5–16 February 1979 in Portugal was a major hydro-geomorphologic extreme event according to the DISASTER database in terms of number of displaced people. The February 1979 event is the top ranked episode in terms of the total number of evacuated people (4244), displaced people (14,322) and also on the number of days of event duration (12 days) for the period 1865–2015. In this event, 62 damaging floods and five damaging landslides causing eight fatalities were recorded in Portugal. This event was driven by an unusually intense atmospheric forcing mechanism acting at different time scales. Despite the intense magnitude and the widespread impact on the population, this event has not been studied in detail. In this study, we show that the precipitation period of February 1979 had produced several multi-day accumulated precipitation events over the Portuguese continental territory, ranking among the top 10 events observed between 1950–2008. Additionally, most of the precipitation from this event occured in days in which atmospheric circulation was dominated by “wet” circulation weather types (CWTs), namely, cyclonic (C), west (W) or southwest (SW) types.
Highlights
It has been well known that extreme precipitation events in Portugal occurring during the extended winter months (October-March) are often associated with landslides and flooding in the major river basins [1,2,3] and, with flash floods in small watersheds or urban areas [4,5] which can produce socio-economic impacts
The 5–16 February 1979 event is the top ranked in the DISASTER database in terms of human impact for each one of the three Portuguese main hydrographic regions affected: Douro, Mondego and Tagus
This event was mainly characterized by progressive flooding occurring along the lowland sectors of each main river’s basin, with the majority of the cases and affected people concentrated along the Tagus river floodplain
Summary
It has been well known that extreme precipitation events in Portugal occurring during the extended winter months (October-March) are often associated with landslides and flooding in the major river basins [1,2,3] and, with flash floods in small watersheds or urban areas [4,5] which can produce socio-economic impacts. ARs are transient filamentary regions of highly concentrated water vapour affected by strong low-level winds that occur within the warm conveyor belt of extratropical cyclones These moisture transport structures typically occur as long (about 2000 Km) and narrow (300–500 km) bands of enhanced water vapour flux at the lower troposphere and are responsible for most of the water vapour transported meridionally across the mid-latitudes, as well as for most of the poleward water vapour transport [10]. Due to their narrow nature, the ARs latitudinal location over the Iberian Peninsula is highly determinative of their contribution to extreme daily precipitation events over Minho, Douro and Tagus basins [9].
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