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Posted 8 June 2011

 

Drought conditions in Europe 2011

Issued by WMO Regional Association for Europe Pilot Regional Climate Centre on Climate Monitoring, Lead Centre (Deutscher Wetterdienst, DWD)

A long-lasting dry period persisted over large parts of Europe from January to May 2011.
According to data of the Global Precipitation Climatology Centre (GPCC), especially the months February to May 2011 had a considerable rain deficit over large parts of Europe. The 4-month totals over this period ranged between 40 and 80% of the long-term mean 1951-2000 over large areas, in many parts of western and central Europe even below 40%; the 3-month totals March to May 2011 were even more extreme (see figures below). France, Germany and southeastern UK appeared to be the most affected areas. Similar conditions occurred in 1976 and in the 1990s.

The United Kingdom had extremely dry conditions from March to May especially in its southeastern parts and experienced its driest March since 1953. The other parts of western and central Europe all had more or less a dry February, March, April and May. 2011 was up to now one of the driest 10 years in nearly whole Switzerland since 1864. In France, the period January to April 2011 was the driest since 1975. April 2011 was one of the 10 driest April months in Germany since 1881, in continuation of similarly dry April months in 2007, 2009 and 2010. The whole spring (March to May 2011) was the driest in Germany since 1893, only a few heavy rain events occurred in May 2011.

Also the preceding winter 2010/11 was very dry at least in western Europe, causing a very low soil moisture during March and April. The reduced rainfall accumulations were coupled with warmer than average temperatures and consequently higher than normal levels of evapotranspiration and plant water requirements. This aggravated the water deficits compared to average seasonal conditions. Agriculture was highly affected in western and central Europe; the growth of crops was lagged much behind usual conditions.

Water levels were very low, particularly in the Rhine River, where shipping was affected in
Germany (German Federal Hydrological Agency). In May, the water levels of most of the German rivers were never as low for this season for about 100 years. The dry conditions were also prone to fires. For example, dune fires broke out in the coastal parts of the Netherlands, and some large fires occurred even in northern parts of the United Kingdom. In some northeastern parts of Germany, the Forest Fire Danger Index reached its highest possible level.

The reason of this long-lasting dry period was a highly persistent high pressure ridge over western and central Europe. Although the North Atlantic Oscillation (NAO) had positive values from February to April 2011 (after a longer period with a negative NAO), which implies a relatively strong air flow over the North Atlantic, this high pressure ridge blocked this airflow, therefore low pressure systems could not reach the European continent. This situation is climatologically a very stable constellation, but it has persisted for an unusually long time.

 
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