The Heavy Rain in Southern Spain during early November 2006
The autumn months usually bring some much-needed rain to the Costa del Sol but the heavy rain that fell between the 6th and 8th of November produced the highest totals in the Malaga area since November 1989, the month of the devastating floods. Introduction
From mid September to early December the Mediterranean Basin is prone to severe storms and, on occasions, rapid and intense cyclogenesis. The main factor causing severe weather at this time of year is the relatively high sea temperature. In early November 2006, after a near record-breaking warm October, sea temperatures were around 2 degrees Celsius above normal and although events in the upper atmosphere generated the widespread instability needed to produce the thunderstorms, it was the extra impetus from the warm seas that was responsible for the high rainfall totals.
5th November, the Plot
Cloudy skies prevailed over much of the Costa del Sol several days before the heavy rains began, but the cloud was of limited depth and trapped in cool air contained beneath a shallow inversion south of the extensive anticyclone covering much of northwest Europe (Fig. 1). The analysis in Figure 1 is too coarse over southern Spain and adjacent seas to show the true extent of east to southeast winds which had reached gale force over open waters south of Malaga. The resulting high seas had come perilously close to inundating beach-side properties west of Malaga (Fig 2.)
Crown Copyright UK Met Office Figure 1. The surface analysis shows a strong anticyclone over northwest Europe and a relatively slack east to southeasterly airflow over southern Spain. Although strong anticyclonic curvature is apparent in the isobars drawn east of Spain, this is insuffiicient to account for the strong to gale force winds.
Figure 2. The grey skies under the shallow inversion accentuate the wild look of the waves as they buffet the coast west of Malaga. On a weekend during the summer this beach is usually packed with sunbathers!
The Rainfall Event Develops
The sheet of stratocumulus cloud persisted throughout Monday the 6th, masking the steady encroachment of high cloud from the southwest. Increasing baroclinicity, manifesting itself in the thickening and broadening of the cloud band over southern Iberia (Fig. 3), prompted the introduction of upper fronts on the surface analysis from the UK Met. Office (Fig 4).
copyright 2006 EUMETSAT Figure 3. Infra-red satellite image for 00UTC 7th November 2006. The main area of convective activity at this time was occurring west of Portugal.
Crown copyright UK Met Office Figure 4. Surface discontinuity close to Iberia was limited to the trough moving slowly southeast near the Portugese coast.
The first rain arrived along the Costa del Sol during the afternoon of the 6th, but Malaga remained dry until after sunset. Spells of moderate rain occurred in the Malaga area overnight on the 6th/7th, and bursts of heavy rain arrived after dawn as the character of the rain became distinctly more convective. A few distant rumbles of thunder were heard to the south around 08UTC and towering cumuliform clouds were observed between the broken layered cloud over the sea (Fig 5). Minor flooding affected roads (Fig 6) before a temporary cessation of the rain occurred with skies brightening.
Figure 5. A temporary lull in the rain on the morning of the 7th allowed cumuliform cloud to be observed under, and towering through, the extensive layered cloud over the sea.
Figure 6. Minor flooding west of Malaga on the morning of the 7th after overnight rain. This rain, amounting to 12 mm (0.5 inches), represented less than 10% of the total fall.
Torrential Downpours in Malaga
From late morning until mid afternoon it became eerily dark in Malaga as a succession of large cumulonimbus clouds moved in from the sea. Lightning and crashing thunder accompanied the heavy rain. Around 25 to 30 mm (1 to 1.2 inches) of rain fell on Malaga rain-guages during the afternoon, although the convective nature of the rainfall probably meant that some areas had considerably more. Temporary flooding occurred, and the City centre, not noted for fast-moving traffic on fine days, almost ground to a halt as several cars spluttered to a standstill in the deepening water (Figs 7,8, 9,10 and 11). The pedestrian precincts were unusually empty (Figs 12,13 and 14) as tourists and locals alike sought refuge in the bars and restaurants waiting for a break in the weather which, as it happened, was a long time in coming.
Figure 7. Principal Alameda Malaga
Figure 8. Principal Alameda Malaga
Figure 9. Malaga from Plaza de la Marina
Figure 10. Plaza de la Marina, Malaga
Figure 11. Paseo del Parque eastbound, Malaga
Figure 12. Calle Marques de Larios, Malaga
Figure 13. Close to Malaga Cathedral
Figure 14. Plaza de la Constitucion, Malaga
...and Worse to Come
In the late afternoon of the 7th the rain became lighter as the frontal clouds, with embedded Cbs, edged slowly eastwards (Figs 15 and 16). By this time, an upper trough, digging southeast from west of Portugal, was creating a cut-off cold pool close to Gibraltar and this, too, was edging slowly east. Temporary subsidence occurred behind the occluding frontal system, marked at the surface by a lowering of air temperatures from 18 to 16 Celsius. However, later in the evening, thunderstorms broke out again and further torrential rain occurred overnight. 7th/8th as the trough, and the associated broad line of convection paid a long visit to Malaga.
Fig 15. Late afternoon west of Malaga as the rain becomes lighter and less convective in nature.
Fig 16. The heaviest clouds edging eastwards over Malaga as evening approaches.
17 Crown copyright UK Met Office Figure 17. The analysis shows the surface cold front which passed through Malaga around 13UTC and Almeria at 18UTC. The slow-moving trough over Malaga eas responsible for some of the heaviest rain of the event.
copyright 2006 EUMETSAT Figure 18. The infra-red satellite picture for 00UTC on 8th November 2006 shows a complex cloud structure over southern and eastern Spain but with a high ratio of cellular elements (convective cloud) to amorphous layered cloud.
The Final Hours
At Malaga Airport, the highest 6-hourly rainfall total of the whole event occurred between 06 and 12UTC as the cold pool, coincident with the surface low (Fig. 17), halted over Malaga before slowly proceeding eastwards again. A trough on the northern side of the upper vortex was slow moving over, and just to the east of Malaga, and further spells of rain lasted into the evening in those parts. West of Malaga, there was dry, bright weather to end the afternoon. During, the evening, though, a further batch of heavy showers developed along the coast before steady stabilisation occurred from the west.
The Aftermath
Although torrents of water running along the old river bed in the centre of Malaga managed to collect several foolishly parked cars and sent them to deeper waters, there was surprisingly little damage considering the water that fell. One factor was the limited extent inland of the heaviest rain which led to less flow from mountain streams into the main river than would have occurred with a more widespread fall. The second factor was the fairly recently constructed flood alleviation scheme on the River Guadalhorce (Figs) The rainfall totals that occured between the 6th and 8th November were the highest in Malaga since the catastrophic floods of November 1989 (Figs ).
Figure 19. River Guadalhorce flood prevention levee soon after completion in 2003. A double levee construction was made to avoid a repeat of the devastating 1989 floods.
Figure 20. November 9th 2006. The River Guadalhorce was higher than normal (mid distance) but contained within the main channel.
Figure 21. The flood plain of the River Guadalhorce during the floods of November 1989. The containers on the right, now disused, are visible in Figure 15.
Figure 22. The flood plain of the River Guadalhorce in November 1989. Malaga Airport is situated about 5 km away mid picture in front of the distant hills.
The new river system coped admirably well with the rain, and although extensive debris found their way into the river, and subsequently on to adjacent beaches (Fig. 22), inspection of the river on the 9th, a fine day with clouds receding across the Sierra Nevada (Fig 23), revealed that all the water had been contained within the main channel.
Figure 22. Debris from the river contained tree trunks and discarded rubbish from 2 years of near drought.
Figure 23. 9th November. Large quantities of silt continued to flow out of the river for several days after the rain ceased.
Conclusion
In the 48 hours between 00UTC on the 7th and 00UTC on the 9th November over 130mm (5.2 inches) of rain fell on Malaga , amounting to nearly 150% of the monthly average. in a few places over 150 mm (6 inches) of rain fell (Fig 24 ). As the rain was split between 2 days, no daily rainfall records were broken, it was wetter on November 14th 2002. However, the 2-day total was the highest in places since the infamous floods of November 1989. In drought-hit southern Spain this was a welcomed rainfall and as one elderly Spanish gentleman was heard to say in Malaga after being completely drenched by the bow wave of a passing lorry, 'we have waited 2 years for this, it's liquid gold'.
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