Storm Desmond, 2015

• Northwest of UK is familiar with heavy rain; combination of warm wet westerly winds and uplands such as Cumbrian fells creates orographic (relief) rainfall. As a result, places in Cumbria are wettest in England e.g Seathwaite averages over 2 meters of rainfall a year. Surprisingly, it occurred twice in a decade - 2005 and 2009. When it happened again in 2015, it was suggested something unusual was happening with local hydrological system.
• Caused by deep Atlantic low-pressure system (depression). Associated fronts stretched across northern Britain, bringing prolonged and heavy rainfall through mechanism known as 'warm conveyor'.
• One theory to explain long periods of wet weather is position of jet stream. Jet streams are driving force which determine direction of depressions and their speed of movement. This band of fast-moving air moves north and south but remained over the northwest longer than usual, bringing in rain-laden depressions from across the Atlantic.
• Mismanagement of land - farmers overgraze land due to sheep and result in bare slopes replacing previously forested areas.
• Mismanaging rivers - combination of raised riverbanks, pumping stations and diversion channels carried surplus water away from built-up areas in Cumbria.
• After 2005 floods, Cumbria installed hard-engineering schemes to estimate how often a flood of a certain magnitude is likely to occur, based on past data. The flood defenses were unfortunately designed for a 1 in 100 year event but floods occurred after 6 years.
• Keswick's flood defences were built to allow river to rise to 5 meters (height it reached in 2009) but in 2015 the river rose 5.9 meters and thus overtopped new defences
• Social impacts:

  • 3000 homes were flooded in 2005 and over 5200 in 2015
  • Residents of flooded properties had to live in temporary accommodation
  • Some local services e.g schools, healthcare, shops and offices were forced to close temporarily
  • Many residents suffered anxiety, stress and psychological damage
• Economic impacts:

  • Many businesses closed and transport and infrastructure (bridges, roads and sewers) were damaged
  • Cost of flooding in Cumbria was £100 mn in 2005, £270 mn in 2009 and £400-500 mn in 2015
  • Insurance claims caused by flooding nationally in 2015 exceeded £6 bn
  • Farmers lost hedgerows and expensive dry-stone walls were washed away; many sheep also drowned
  • Risk of repeated flooding deterred tourists from visiting
• Environmental impacts:

  • many river banks eroded, adding to future flood risk
  • Rivers choked with debris and contaminated with sewage and effluents and pollutants
  • Soils eroded, habitats destroyed and ecosystems affected
  • Saturated ground led to decomposition of dead plants and animals - giving off noxious grapes such as hydrogen sulphide. Other poisons contaminated food chain and threatened wildlife.
  • Saturated ground also led to landslides