Mesoscale numerical analysis of the historical November 1982 heavy precipitation event over Andorra (Eastern Pyrenees)

Abstract

Abstract. From 6 to 8 November 1982 one of the most catastrophic flash-flood events was recorded in the EasternPyrenees affecting Andorra and also France and Spain with rainfall accumulations exceeding 400 mm in 24 h, 44 fatalities and widespread damage. This paper aims to exhaustively document this heavy precipitation event and examines mesoscale simulations performed by the French Meso-NH non-hydrostatic atmospheric model. Large-scale simulations show the slow-evolving synoptic environment favourable for the development of a deep Atlantic cyclone which induced a strong southerly flow over the Eastern Pyrenees. From the evolution of the synoptic pattern four distinct phases have been identified during the event. The mesoscale analysis presents the second and the third phase as the most intense in terms of rainfall accumulations and highlights the interaction of the moist and conditionally unstable flows with the mountains. The presence of a SW low level jet (30 m s −1 ) around 1500 m also had a crucial role on focusing the precipitation over the exposed south slopes of the Eastern Pyrenees. Backward trajectories based on Eulerian on-line passive tracers indicate that the orographic uplift was the main forcing mechanism which triggered and maintained the precipitating systems more than 30 h over the Pyrenees. The moisture of the feeding flow mainly came from the Atlantic Ocean (7-9 g kg −1 ) and the role of the Mediterranean as a local moisture source was very limited (2-3 g kg −1 ) due to the high initial water vapour content of the parcels and the rapid passage over the basin along the Spanish Mediterranean coast (less than 12 h).

Circulation weather types associated with extreme flood events in Northwestern Mediterranean

“…This type was linked to floods associated with low pressure on the Galician coast (NW IP). One of these situations caused the well‐known flood event of 6–8 November 1982, which seriously affected the Pyrenees (Spain, France and Andorra) following rainfall of over 400 mm (up to 610 mm), which led to landslides, widespread damage and more than 40 deaths (Trapero et al , ).…”

Meteorological Driving Mechanisms and Human Impacts of the February 1979 Extreme Hydro-Geomorphological Event in Western Iberia

“…The deadliest storm affecting Portugal since at least the early 19th century took place on 25 and 26 November 1967, causing more than 500 fatalities [4]. In addition, between 6-8 November 1982, there occurred one of the most catastrophic flash-flood events in the Eastern Pyrenees affecting Andorra and also Southern France and Eastern Spain with rainfall accumulations exceeding 400 mm in 24 h with 44 fatalities and widespread damage [27]. Finally, on 5 November 1997, extreme precipitation with values higher than 150 mm in 24 h in Southern Portugal and Extremadura province in Spain produced major flash flood events, causing major socio-economic impact with 11 deaths in Portugal and 21 in Spain [20].…”

Trends in flash flood events versus convective precipitation in the Mediterranean region: The case of Catalonia

“…Damage produced by catastrophic floods of this kind includes the total or partial destruction of infrastructure, power cuts, urban floods, agricultural and livestock losses, and, frequently, loss of human life. The November 1982 event that affected the north-east of Spain, Andorra and the south-east of France (Trapero et al, 2013), and the Gard event of September 2002, are an example (Braud et al, 2010;Milelli et al, 2006). (iii) Type 3 or Extended Floods (EF): these are the least frequent type in this region.…”