2007 United Kingdom Floods - Meteorological Background

Meteorological Background

June 2007 started quietly with an anticyclone to the north of the United Kingdom maintaining a dry, cool easterly flow. From 10 June the high pressure began to break down as an upper trough moved into the area, triggering thunderstorms that caused flooding in Northern Ireland on 12 June.

Later that week, a slow moving area of low pressure from the west of Biscay moved east across the British Isles. At the same time, an associated occluded front moved into Northern England, becoming very active as it did so with the peak rainfall on 15 June. Rainfall records were broken across the region, leading to localised flooding. As it weakened, the front moved north into Scotland on 16 June and left England and Wales with a very unstable airmass, frequent heavy showers, thunderstorms and cloudy conditions. This led to localised flash flooding and prevented significant drying where earlier rains had fallen.

On 25 June another unseasonably low pressure (993 hPa / 29.3 inHg) depression moved across England. The associated front settled over Eastern England and dumped more than 100 mm (3.9 in) of rain in places. The combination of high rainfall and high water levels from the earlier rainfall led to extensive flooding across many parts of England and Wales, with the Midlands, Gloucestershire, Worcestershire, South, West and East Yorkshire the most affected. Gales along the east coast also caused storm damage. RAF Fylingdales on the North Yorkshire Moors reported rainfall totals of 103 mm (4.1 in) in 24 hours, an estimated 100 mm (3.9 in) in Hull and 77 mm (3 in) on Emley Moor in West Yorkshire. The average monthly total for June for the whole UK is 72.6 mm (2.9 in).

On 27 June, the Met Office released an early warning of severe weather for the approaching weekend, stating that 20 to 50 mm (–2 in) of rain could fall in some areas, raising the possibility of more flooding within the already saturated flood plains.

On 20 July, another active frontal system moved across Southern England. Many places recorded a month's rainfall or more in one day. The Met Office at RAF Brize Norton in Oxfordshire reported 126.6 mm (5 in): a sixth of its annual rainfall. The college at Pershore in Worcestershire reported 142.2 mm (5.6 in), causing the Environment Agency to issue 16 further severe flood warnings. By 21 July, many towns and villages were flooded, with Gloucestershire, Worcestershire, Warwickshire, Wiltshire, Oxfordshire, Berkshire, London and South Wales facing the brunt of the heavy rainfall.

Climate researchers have suggested that the unusual weather leading to the floods may be linked to this year's appearance of La Nina in the Pacific Ocean, and the jet stream being further south than normal.