[2] Western Europe saw a series of extratropical cyclones forming in a westerly flow over the Atlantic, directing warm and moist air to the region.

A situation developed in a similar manner to that seen during the Autumn 2000 western Europe floods, which saw catchments and soils becoming increasingly saturated.

[4][5][6] Storm Desmond broke the United Kingdom's 24-hour rainfall record, with 341.4 mm of rain falling at Honister Pass, Cumbria, on 5 December 2015.

The heavy rainfall caused a waterfall to appear at Malham Cove for a short period of time; this had not previously happened in living memory.

[14] Part of the A591 road an important north-south artery between Grasmere and Keswick in the Lake District, was washed away at Dunmail Raise with a landslip occurring adjacent to Thirlmere.

[15][16] In the Republic of Ireland, the worst affected areas were the province of Connacht and counties Donegal, Westmeath, Tipperary, Limerick, Clare, Cork and Kerry.

Millions of euros worth of damage was caused in Bandon, Fermoy, Kenmare and Tralee, while the Blackpool area of Cork City was severely affected by a high level of water flow in the River Lee.

In Glaslough, County Monaghan, the dead body of a 70-year-old man was found when his car was believed to have become trapped in a dipped part of a flooded road.

[18] Approximately 1,000 people were evacuated from their homes in the town of Hawick in the Scottish Borders as a result of the River Teviot flooding.

[22] In Wales, heavy rainfall led to flooding close to Llandygai, near Bangor in Gwynedd, with RNLI coastguard helicopters rescuing one person from their car.

Eva was the fifth storm to be officially named by Met Éireann on 22 December 2015, with an orange wind warning being issued for counties Clare, Galway, Mayo, Sligo and Donegal.

[28] Liz Truss convened a COBRA meeting to decide on emergency measures, which included the deployment of soldiers from the 2nd Battalion, Duke of Lancaster's Regiment[29] to the affected areas.

One explosion and subsequent fire occurred as a result of a footbridge being swept away by the River Irwell, with footage of the incident being widely shared on social media.

[39] In York, the Environment Agency were forced to open the Foss Barrier which has protected the city centre since 1987, as the control room had become flooded and the pumps were in danger of failing.

In the Scottish Premiership, waterlogged pitches led to the postponement of fixtures between Dundee United and Motherwell and between Partick Thistle and St Johnstone.

[49] The Lancashire Fire and Rescue Service and North Wales Police warned motorists not to travel unless absolutely necessary, with heavy rainfall and high winds leading to widespread road closures.

[53] The Times reported that senior politicians regarded the floods as being the result of extreme weather caused by climate change.

[61] On 4 January, Network Rail announced the West Coast Main Line between Carlisle and Glasgow would be closed until 1 February, with passengers either diverted through Dumfries or transferred to coaches due to significant damage to the Lamington Viaduct.

Up to 70 properties were evacuated in total and the impacts of the storm caused disruption to rail, road, air travel, power cuts and school closures.

The dynamic nature of the underlying climate conditions behind such assumptions has also been questioned,[68] with the Environment Agency stating that a "complete rethink" of the UK's flood defences is needed.