Case study: the Cumbrian floods 2015

In December 2015, Storm Desmond set a new record, with 341.4 millimetres of rain falling over a 24-hour period. This led to the flooding of Cumbria and in particular, the town of Cockermouth - despite the construction of a self-closing flood barrier in 2013.

Physical causes

The warm air from the mid-Atlantic caused relief rainfall over the Cumbrian Mountains. The warmer the air, the more moisture it holds.

Warm air from the mid-Atlantic was forced up the Cumbrian Mountains by prevailing winds. As the air cooled, it condensed to form heavy rain, pouring into the River Derwent and River Cocker.
  1. Warm air from the mid-Atlantic moved towards land due to the prevailing wind.
  2. The warm air was forced upwards by the Cumbrian Mountains.
  3. As the air cooled, it condensed to form heavy rain. The weather front stopped over Cumbria and this heavy rain fell on land that had already been saturated.
  4. The falling rain poured into the River Derwent and River Cocker.
  5. Cockermouth is located at the rivers' confluence and as a result, led to significant flooding.

Human causes

A number of homes and businesses had been constructed on the flood plains of the local rivers.



  • Over 43,000 homes across Cumbria and Lancashire suffered from power cuts.
  • Approximately 5,200 homes were affected by flooding.
  • One person died in Cumbria.
  • About 40 schools closed in Cumbria.


  • Rail and road services were disrupted.
  • Many businesses suffered through damage to property and stock.
  • The estimated cost was £500 million across Cumbria. The government provided £50 million for flood victims and businesses.
  • Insurance companies have been predicted to pay out up to £325 million to residents and businesses.


  • Rivers were significantly altered with increased rates of erosion.
  • Landslides and mudslides were reported
  • Heavy rain washed nutrients from soil.
  • Vegetation was flooded causing habitat loss.
The River Derwent flooded homes in 2009
The River Derwent burst its banks in 2009 and again in 2015, leading to extensive flooding of homes and businesses in Cockermouth

Reducing the risks

Following the earlier 2009 floods in Cockermouth, a flood prevention scheme was implemented. River dredging was used to increase the capacity of the river channel so it could hold more water in the future. A self-closing flood barrier was also installed in 2013 to increase the height of the river banks - however, the record breaking rainfall of December 2015 was too much for the barrier to contain.

Alerting people to the risk of potential flooding enables the public to evacuate the area, reducing injuries and deaths. Economic losses can also be reduced as people and businesses can move their valuables to a safer area. The government has pledged to spend £2.3 billion on flood defences between 2016 and 2022.

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