Extreme rainfall in Cumbria, November 2009 - an assessment of storm rarity

A new UK record was established at Seathwaite Farm, Borrowdale recently, when 316.4 mm of rainfall was recorded over the 24-hour period up to 00:00 on 20th November 2009. This exceptional event followed several days of heavy rainfall, and caused widespread flooding in Cumbria, which particularly affected the communities of Cockermouth and Workington and extended into south-west Scotland. Drawing on the results of a recent project which has developed a new model of point rainfall depth-duration-frequency (DDF) for the UK, return periods are estimated for rainfall observations available for the Cumbrian event at two raingauge sites. The new model has been designed as a replacement for the Flood Estimation Handbook (FEH) rainfall model and has been specifically developed to apply to very extreme events. The paper demonstrates how valuable even relatively short raingauge records can be in upland areas such as the Lake District in improving estimates of storm frequency.