Flooding in southern Spain

Flooding in southern Spain

04 December 2016 12:12 UTC

Flooding in southern Spain
Flooding in southern Spain

Tropical air trapped in Gulf of Cadiz caused severe flooding in southern Spain in December 2016.

Last Updated

14 November 2020

Published on

04 December 2016

By Fausto Polvorinos (AEMET), Carla Barroso (IPMA), Djordje Gencic (RHMSS) and Vesa Nietosvaara and José Prieto (EUMETSAT)

Continuous rain affected the southern part of the Iberian peninsula on 3 and 4 December, causing severe flooding and casualties in various coastal locations and in the larger towns of Lisbon and Malaga. Extreme precipitation in Andalusia (southern Spain) frequently coincides with tropical air arriving over the Azores anticyclone, alternatively straight from the tropical Atlantic, following a narrow and penetrating pattern called a moisture river. This increased the total area of rain over the affected regions (green dots on Figure 1, above right).

 In the previous days, an atmospheric river was feeding the area with humid air from the Brazilian area.
Figure 1: In the previous days, an atmospheric river was feeding the area with humid air from the Brazilian area.

On Sunday 4 December two frontal systems, with moderate convective activity, as can be seen from the Meteosat-10 infrared 10.8 µm and HRV images on Figures 2 and 3, were located over land at a few hundred km distance from each other, progressing towards the north east.

 
 Met-10, 04 December, 12:12 UTC
Figure 2: Met-10 IR10.8, 04 December, 12:12 UTC
 
 Met-10, 04 December, 12:12 UTC
Figure 3: Met-10 HRV, 04 December, 12:12 UTC.
Note also the föhn gap caused by the central mountains in Spain (marked in red)

The imagery in Figure 4 and 5 show the connection of the frontal cloud with standard NWP parameters.

 Met-10, 04 December, 12:00 UTC
Figure 4: Met-10 HRV with cyan lines for the 500 HPa topography, 04 December, 12:00 UTC.
 
 NWP parameters, 04 December, 12:00 UTC
Figure 5: NWP parameters, 04 December, 12:00 UTC
Indicates the vorticity advection (positive in red, negative in blue lines) for the cross section marked by the thick green line on Figure 4.
 ASCAT 25 km winds (Credit: NOAA)
Figure 6: ASCAT 25 km winds (Credit: NOAA)

The combination of easterly winds in the Alboran sea (western Mediterranean) (shown on Figure 6) and the low pressure circulation west of Gibraltar trapped a 'river' of tropical air coming from the west, causing locally torrential downpours over that mountainous coast.

Up to 200 mm of rain fell in Estepona and Marbella , 30% of the annual average — Marbella had 81 mm in an hour (Figure 7). It was reported they were the worst floods the region had seen for 30 years.

Several features in the animations indicate severity: fast cooling and expansion at the cloud tops between 06:30 and 08:30 UTC on 4 December, overshooting tops at 07:45 and 08:15 UTC, brightness at the sunny side of the cloud in the solar channels, and the dry C-shaped dark band in the water vapour imagery (not shown) at the wind side of the anvil, indicating rapid descents near the deep convection.

The low pressure circulation affected Lisbon with 87 mm in 24 hours on Sunday 4 December.

 Precipitation gauged on 4th December by the
Figure 7: Precipitation gauged on 4th December by the local rain network.

Both the Dust RGB animation and sandwich product animation summarise the weather evolution on 3 and 4 December. The Dust RGB is based on the thermal window channels of SEVIRI. The sandwich product replaces the HRV pixel information with coloured IR 10.8µm brightness temperatures (BT), usually from 200 to 240K, for pixels showing BT values in that interval.


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