Extreme weather in Southern France

Another Record Rainfall in Southern France

Weather Undeground,

30 September, 2014

It is hard to believe that another rainstorm of equal intensity to that which I blogged about just 11 days ago has again struck the Languedoc Region of Southern France. This time the focus of the storm was centered over the city of Montpellier, Herault District, near the Mediterranean Coast.

Rue Broussonnet in Montpellier provided a new definition of ‘car pooling’ during the record-setting deluge Monday afternoon, September 29th when almost 10” of rain fell in three hours. Photo by Benoit from Tournemire.

Montpellier, a city of some 240,000, was deluged with an all-time 24-hour record 299 mm (11.77”) of rainfall between 8 a.m September 29th and 8 a.m. (local time) September 30th. This is the equivalent of almost four times the average monthly precipitation for September in the city. Its previous 24-hour rainfall record for September was 187 mm (7.36”) on September 22, 2003 and its all-time record 205 mm (8.07" on October 25, 1979. Some private weather stations in Montpellier reported totals of up to 325 mm (12.80”) according to a German weather forum monitored by Michael Theusner of Klimahaus in Bremerhaven, Germany.

Of the official 299 mm total in Montpellier, an amazing 184 mm (7.24”) of this fell in just two hours between 3 p.m. and 5 p.m. on Monday (September 29th) and 252 mm (9.92”) in three hours from 3 p.m. to 6 p.m. Here is the rainfall by time period beginning the morning of September 29th:

8 am-2 p.m.: 13 mm (0.51”)

2 p.m.-3 p.m.: 17 mm (0.67”)

3 p.m.-4 p.m.: 91 mm (3.58”)

4 p.m.-5 p.m.: 93 mm (3.66”)

5 p.m.-6 p.m.: 68 mm (2.68”)

6 p.m.-7 p.m.: 5 mm (0.20”)

7 p.m.-8 p.m.: 3 mm (0.12”)

8 p.m.-8 a.m. (Sept. 30): 10 mm (0.39”)

Graph and table of hourly (local time) rainfall at Montpellier Airport from Monday morning to Tuesday morning, September 29-30. (Note: the above totals amount to 300 mm instead of the official 299 mm because of rounding of figures. This also applies to totals expressed in inches). Source: Meteo France.

The two-hour total would be a new French national record for rainfall intensity, surpassing the 180 mm (7.09”) measured at Saint-Gervais-sur-Mare just 13 days ago on September 16th! Prior to this month’s extreme rainfalls, the previous greatest two-hour rainfall total observed in France was 178.4 mm (7.02”) at Solenzara on October 26, 1979. However, it should be noted that records in France for short-duration rainfalls only go back to the 1960s or 1970s and do not include every meteorological site in the country. Nevertheless, it is pretty shocking that two such amazing rain events have occurred in the same region over just a two-week period. Fortunately, unlike the September 16-18 event (when four died), it appears that, so far, no known fatalities have occurred with the storm in Montpellier.

The rainfall was concentrated directly over Montpellier as this map of accumulations illustrates:

Map of accumulated rainfall in millimeters for the 48-hour period ending at 6 a.m. UTC September 30th. Montpellier is located in that bull’s eye of 250 mm+ accumulations. The white area below Montpellier is the Mediterranean Sea. Map from Meteo France.

Other rainfall reports from the region were impressive although not close to that of Montpellier:

160 mm (6.30”) at Pezenas

156 mm (6.14”) at Beziers

153 mm (6.02”) at Prades-Le-Lez

124 mm (4.88”) at Narbonne

88 mm (3.46”) at Perpignan

Map of Languedoc-Roussillon region in southwestern France with location of Montpellier and some of the other cities mentioned above.

The storm brought this September’s total rainfall amount to 350 mm (13.78”), which is also a new monthly record (previous record being 293.2 mm (11.54”) in September 2003.

The cause of the intense rainfalls in both cases of September 16-18 and September 29 is an atmospheric set-up that is typical during the autumn in this part of the Mediterranean region (including Spain and Italy): warm, humid air flowing off the Mediterranean Sea collides with cooler dry air emanating from the Alpine region while a cold upper-air low rests over the area. Most of the greatest rainfall events in Spain, France, and Italy have occurred during September and October when this type of scenario is in play.

Meanwhile, the U.K. has wrapped up its driest September on record. More about that later.

KUDOS: Thanks to Michael Theusner of Klimahaus, Bremerhaven, Germany and Maximiliano Herrera for bringing this to my attention.

Christopher C. Burt

Weather Historian