Wednesday 9 December 2015

Atlantic Storm Desmond causes three fatalities, widespread flooding.

Three fatalities have been confirmed in the wake of Atlantic Storm Desmond, which passed over the UK and Ireland on Saturday 5-Sunday 6 December 2015. Two drownings were reported, one in Cumbria in northwest England the other in County Monoghan, in the Republic of Ireland, while a third victim was reportedly blown under a bus in London. All three fatalities have been described as elderly men. The storm also caused widespread flooding, across Ireland, the Isle of Man, northwest England and parts of Wales and Scotland.

Flooding in the town of Appleby in Cumbria during Atlantic Storm Desmond. Owen Humphreys/PA.

In the Republic of Ireland widespread flooding was reported in the counties of Donegal, Galway, Letrim, Mayo, Roscommon, Sligo, Kerry, Cork and Claire, with the towns of Tralee, Kenmare and Bandon being particularly badly hit. About 2000 homes were left without power following the storm, mostly on the west coast of the country. Numerous roads were flooded across the country, and Dublin Airport was forced to close and ferries between Dublin and Holyhead were suspended on Saturday 5 December due to high winds, with windspeeds as hogh as 120 kilometers per hour being recorded.

Flooding at Westport in County Mayo. Paul Mealey/Irish Mirror.

On the Isle of Man the storm began causing problems on Thursday 3 December, causing widespread flooding and several landslides. Landslides are a common problem after severe weather events, as excess pore water pressure can overcome cohesion in soil and sediments, allowing them to flow like liquids. Approximately 90% of all landslides are caused by heavy rainfall. A 200 year old bridge collapsed at the height of the storm, depositing a double decker bus in the River Laxey, though nobody was hurt in this incident. Ten people were evacuated from their homes in Laxey.

A bus deposited in the River Laxey on the Isle of Man during Atlantic Storm Desmond. Manx Telecom.

In Wales flooding was reported in Gwynedd, Powys, Swansea and on Anglesey, and winds of 134 kilometers per hour were recorded in Snowdonia National Park. Around 700 homes were left without power in Denbighshire, Gwynedd and Conwy. Train services between Bangor and Holyhead were suspended due to high winds and debris on the lines, and between Bangor and Llandudno Junction after a wooden hut blew onto a line and collided with a train.

A car washed into a river near Bangor in Gwynedd during Atlantic Storm Desmond. Menei Photography.
In England over 6000 homes were flooded across Cumbria and Lancashire, with around 42 000 homes without power in Lancashire and 43 000 more across Yorkshire and Lincolnshire. Train services across northwest England were disrupted and on many lines suspended completely.Leeds Bradford Airport was temporarily closed due to high winds and the River Tyne was recorded as reaching 6.9 m, the highest water level in 61 years. Schools and other public services across much of Lancashire and Cumbria were forced to close, as was the University of Lancaster.

Rescue workers on a flooded street in Carlisle. Phil Noble/Reuters.

In Scotland about 1000 people were evacuated from their homes in the town of Harwick in Scottish Borders, and part of the city of Dumfries was flooded after the River Nith burst its banks. Many roads were closed due to flooding and landslides, and rail services between Glasgow and England were severely disrupted.

Flooding in Renfrewshire, Scotland, during Atlantic Storm Desmond. Peter Sandground/Barcroft Media.

Ocean storms form due to heating of air over the sea in tropical zones. As the air is heated the the air pressure drops and the air rises, causing new air to rush in from outside the forming storm zone. If this zone is sufficiently large, then it will be influenced by the Coriolis Effect, which loosely speaking means the winds closer to the equator will be faster than those further away, causing the storm to rotate, clockwise in the northern hemisphere and anticlockwise in the southern hemisphere.

 Flooding at Castlefynn in County Donegal. Artur Widak/NurPhoto/Corbis.

Whilst the high winds associated these storms is extremely dangerous, the real danger from such storms is often the flooding. Each millibar drop in air pressure can lead to a 1 cm rise in sea level, and large storms can be accompanied by storm surges several meters high. This tends to be accompanied by high levels of rainfall, caused by water picked up by the storm while still at sea, which can lead to flooding, swollen rivers and landslides; which occur when waterlogged soils on hill slopes lose their cohesion and slump downwards, over whatever happens to be in their path.

 Flooding at Ambleside in Cumbria. Ashley Cooper/Barcroft Media.

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