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2019 Yorkshire Dales floods

July 2019 floods in northern England

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The flood was described as being a 1-in-100 year event with one newspaper report later describing the conditions as being "monsoon-like weather".

Background

Meteorological history

Average annual rainfall in the Pennines is 59 inches (1,500 mm) which drops away at the east coast where the average is 24 inches (600 mm). The Pennines are known to be part of the rain shadow in the United Kingdom; this is due to the prevailing westerly winds dropping precipitation on the western side of the country and leaving the eastern side drier. Comparisons can be made between Manchester, on the western side of the Pennines, and Sheffield on the eastern side. These two cities are 35 miles (56 km) apart, and 128 feet (39 m) and 433 feet (132 m) above sea level respectively. Manchester's average rainfall is 33.8 inches (858 mm) and Sheffield's is 31.6 inches (802 mm). Between the two cities is the Peak District, which has the same effect as the Pennines, dropping more rain on the west than on the east. Of the top ten rainiest cities or towns in England, only Huddersfield, in Yorkshire, is on the eastern side of mainland Britain; the rest are on the west side of the rain shadow.

The wettest location in the Yorkshire Dales is Snaizeholme (near to Widdale) 1,900 feet (579 m) above sea level, and where the average annual rainfall is 77 inches (1,957 mm). The Yorkshire Dales (and the Howgill Fells) have suffered historical flooding in 1870,1890, 1899 and 1986 (Hurricane Charley). The floods of January 1890 swept away the bridge over the Swale at Gunnerside.

Peak flooding has also been recorded in the 1940s, the 1960s and the 1980s. Flash floods have affected the area throughout the 21st century, with events occurring in 2009, in June 2012, and September 2012 which closed the A1 road. In 2016, a flash flood inundated the White Scar Caves visitor centre.

Most of these flood events have been described as "intense, highly localized convectional summer storms, under anticyclonic conditions, or by slow moving or near-stationary fronts." This can be seen in the fact that the area where the water fell, was concentrated in a 4-mile (6.4 km) radius around the town of Reeth; places like Bellerby and Leyburn suffered as a result of rainfall elsewhere, whereas Richmond, 10 miles (16 km) to the east, was described as having no rain at all on the day of the floods.

Most flooding events in Britain have been the result of a climatic condition known as the North Atlantic Oscillation (NAO-) when it has been in a negative phase, which can lead to wetter seasons. Records indicate that the River Swale has had 145 flash flood events between 1700 and 2013. Flooding in Swaledale, Wensleydale and Nidderdale, usually results in flooding on the River Ouse in York.

Physical causes

On the 30 July 2019, the Yorkshire Dales and east Cumbria regions experienced extreme above average rainfall from what is typically expected in the summertime. Malham Tarn in the Craven District of Yorkshire, typically receives 3.5 inches (89 mm) of rain as a monthly average; on the 30 July 2019, 3.2 inches (81 mm) fell in a 24-hour period, with most of that actually falling within four hours. Langthwaite in Arkengarthdale, was stated to have received 5.2 inches (132 mm) in two hours, and Arkle Town received 4 inches (102 mm), with 3.2 inches (82 mm) of that falling in 90 minutes.

Over 7.7 square miles (20 km2) of land around the village of Reeth, was listed as having been inundated with over 2,100,000 litres (460,000 imp gal; 550,000 US gal) in just under five hours. A report later stated that this was enough water to fill over 800 Olympic-sized swimming pools.

The same weather front caused flooding in South Manchester, East Cheshire and Whaley Bridge in Derbyshire which lead to the town being partly evacuated in case the damaged reservoir failed and caused an extreme flood event.

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