Torrential downpours in southern Europe

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  • Flash floods are not unusual in Northern Italy. Photo: Prisma Fotogiornalismo/PA Archive/Press Association Images

    Precipitation amount for the 24 hours up to 1200UTC on Sunday, as predicted by ECMWF.

    Precipitation amount for the 24 hours up to 1200UTC on Monday, as predicted by ECMWF

  • Torrential downpours in southern Europe
    05.11.2011 17:48

     

    A potent synoptic situation has caused days of heavy rain across northern Spain, southern France and northern Italy, leading to major problems associated with severe flash flooding. Reports of loss of property and, tragically, loss of life have raised the awareness of the current meteorological conditions.

    The trigger for the downpours over the past few days has been a low pressure system situated east of Spain drawing cold air over the warm waters of the Mediterranean. This process causes air to become highly unstable, in turn producing intense showers and thunderstorms. Although such events are far from unknown at this time of year, very impressive precipitation totals have been recorded nonetheless. Precipitation has remained relatively stationary over southern Europe due to slow-moving fronts originating from North-Atlantic depressions. As such, ground has become saturated leading to large amounts of runoff and little relief for the hardest-hit areas.

    The problem is compounded in this particular part of Europe due to widespread areas of elevated topography causing a funneling of surface runoff into low-lying, and often highly populated, areas. High ground also has a direct effect of enhancing precipitation that is already falling by forcing warm, moist air to rapidly cool and condense. In a potent synoptic situation such as this, the “orographic” enhancement can be devastating.

    One of the worst hit locations in the past few days has been Genoa, a major seaport in north-west Italy with a population of over 600,000. Torrential downpours 20 miles north at Passo Dei Giovi gave109 mm of precipitation in the 12-hour period to 1800UTC last Friday, which is around equal to a full month’s total in the area. This caused devastating flash flooding downstream in Genoa, with large volumes of surface water tearing through streets across the city. The flooding caught many people by surprise, such was the intensity of the rainfall, killing at least six people who had tried to seek shelter.

    Elsewhere, 94.2 mm of rain fell at Nimes in Gard region of southern France in the 24-hour period to 1800UTC on Friday. With average rainfall for November in southern France being just over 60 mm, it is of no surprise that there were flash floods and damage to property across the region. Another notable total was 75.0 mm overnight at Bilbao, northern Spain on Friday 4th November.

    Whether there will be any further problems across southern Europe will mainly be down to the location and/or intensity of precipitation in the coming days. Weather forecast models suggest mixed fortunes across the region, with northern Spain faring better due to a cold front clearing eastwards and taking with it the heaviest precipitation. However, with Italy directly in the cold front’s path, further storms are anticipated not only across northern areas but also as far south as Sardinia. This could spell major problems, especially in places already affected by localised flooding.

    By: Nick Prebble