Storm Christoph

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Storm Christoph brought strong winds, heavy rain and snow to the UK between 19 and 21 January 2021. The most intense rainfall occurred over north Wales and northern England, bringing localised flooding to many areas. The Environment Agency (EA) and Natural Resources Wales (NRW) issued flood warnings across much of the two countries including severe flooding warnings on the River Mersey, River Bollin and the English and Welsh River Dee. Approximately 3,000 people were evacuated from their homes.

Impact to property was not as severe as feared, with estimates ranging from 400 to 600 residential properties (EA, 2021a & Guardian, 2021) and around 100 commercial premises affected. The Environment Agency reported that 38,000 properties were protected by flood defences (EA, 2021b), though many defences, including those along the River Mersey in Didsbury, came within centimetres of being overtopped during the event.

METEOROLOGY AND FLOOD FORECASTING

The Met Office reported that 50 to 100mm of rain fell widely across Wales and north-west England, with over 100mm across upland areas of Wales, south-west England, the Lake District and the Pennines (Met Office, 2021). At several locations over 100% of the January monthly average rainfall fell between 18 and 20 January.

Source: Met Office Storm Christoph Summary

JBA’s flood forecasting system Flood Foresight continuously monitors rainfall and river flow conditions across the UK. Five days in advance Flood Foresight indicated that flooding following Storm Christoph had the potential to impact property. At three days and one day in advance, we published maps indicating the areas potentially at risk as the forecast became more refined. In the sequence of images below these maps are compared to the flow conditions on 21 January and the areas where JBA’s Event Response team and the Environment Agency reported property flooding.

Sequence of areas forecast to be affected by Flood Foresight. Top left, three days in advance, top right, one day in advance and below, comparison to the reported number of properties affected. Source: Environment Agency and JBA.

IMPACTS BY REGION: WALES

Across Wales, NRW issued 46 flood warnings, with two severe flood warnings indicating a potential threat to life. On 20 January, a major incident was declared as the River Dee threatened to inundate property in Bangor-on-Dee; 30 people were evacuated from their homes. On 21 January, the river peaked at a record-breaking 16.46m causing widespread property damage. In Wrexham and areas of Flintshire, flooding from the River Alyn and River Clywedog caused significant damage to properties and commercial premises. In Ruthin, Denbighshire, the River Clwyd caused at least 15 properties on Clwyd Street to be flooded 0.6-0.9 metres deep after flood waters breached temporary defences (DailyPost, 2021, Denbighshire free press, 2021).

JBA Risk Management’s 1-in-75-year flood map, Bangor-on-Dee, compared to observed flooding during Storm Christoph. Image credit: WalesOnline.

In the village of Skewen in Neath Port Talbot, around 80 people were evacuated on the afternoon of 21 January as flood water from a disused mine works erupted to the surface inundating property and cars in several streets. The cause is being attributed to one or more mine shafts being inundated by a considerable amount of rainwater, which rushed into the abandoned mines leading to potential blowouts.

Aerial image of flooding in Skewen caused by mine working blowout. Image credit: South Wales Police

As of 25 January, the river levels across north Wales remained high and a number of roads were still considered unsuitable for traffic due to debris and surface water.

IMPACTS BY REGION: CHESHIRE & GREATER MANCHESTER

Across Cheshire and Greater Manchester more than 87 flood warnings were issued between 19 and 22 January, with severe warnings indicating the potential of ‘threat to life’ (Flood Warning Information Service, 2021).

Across Warrington, Northwich, Chester, Ellesmere Port and Tattenhall more than 150 people were evacuated from their homes (Cheshire Fire Service, 2021). Evacuations by police and fire services across the county continued over the following 48 hours with Warrington and Northwich being particularly badly affected by flooding (Northwich Guardian, 2021).

In Warrington, the river Sankey Brook peaked at 5.9m at 4:45pm on 20 January, causing flooding in Dallam, Bewsey and Sankey Bridge, inundating 200 properties (EA, 2021a). The water level on the River Weaver at Northwich peaked at 3.57m at 10:45am on 21 January. Reports suggest that river defences held, but that surface water flooding inundated the town (CheshireLive, 2021). Analysis by JBA’s Event Response team indicates both riverside premises and the main high street were affected, with 39 commercial properties flooded (TheStandard, 2021). Elsewhere across Cheshire West and Chester, the Environment Agency reported that 52 properties were flooded (EA, 2021a).

(Pictured right) Rostherne Close, Sankey Bridge, Warrington inundated on 20 January, comparison to JBA’s 1-in-20-year flood map. Image credit Manchester Evening News.

Across Greater Manchester intense rainfall led to high river flows on both the River Irwell, inundating riverside walkways in central Manchester, and the River Mersey, leading to the Environment Agency issuing a severe flood warning. Approximately 2,000 homes in Didsbury and Northenden were evacuated on the evening of 20 January as the Environment Agency filled the Didsbury basin – a flood storage basin, immediately adjacent to the river. The river level peaked at 7.1m at Didsbury and a record high of 3.27m at Northenden in the early hours of 21 January. Flood waters were reported to be ‘centimetres away’ from the top of the 1-in-150-year flood defences. If these defences had been overtopped 2,300 properties would have been inundated.

(Pictured left) River Mersey beginning to recede on 21 January with Didsbury flood basin full, protecting an estimated 2,300 homes in South Manchester. Image credit: Manchester Evening News

In Wigan, commercial premises in the Saddle junction area were inundated, with the Environment Agency reporting 25 properties flooded (EA, 2021a). In nearby Leigh, several properties in the Higher Folds area were affected by surface water flooding.  

IMPACTS BY REGION: YORKSHIRE

The Environment Agency issued 123 flood warnings across Yorkshire during Storm Christoph. In West Yorkshire, the River Aire inundated the floodplain at several locations, including near Bingley and Castleford. Despite flood warnings, the River Calder did not cause significant flooding and unlike during Storm Ciara in 2020, there were no reports of property flooding.

The River Ouse at York peaked at 2:45am on 22 January at 4.64m, causing riverside flooding to premises and streets in the city centre. Around 130 homes in York were evacuated (Examiner Live, 2021). Further east at Stamford Bridge, the River Derwent peaked at 9.69m, at 12:15am on 22 January and caused flooding to riverside property. In Malton, North Yorkshire, the River Derwent peaked at 4:15am on 22 January at a record high level of 5.05m with property affected in Malton and in neighbouring villages, including Fryton, from Wath Beck. (BBC, 2021). Fire crews pumped water from premises in Selby, Tadcaster, Helmsley and Harrogate (North Yorkshire Fire & Rescue Service, 2021).

Malton, Yorkshire where the River Derwent flooded adjacent property. Image Credit: Ngarbuttmoor, Twitter.

SUMMARY AND OUTLOOK

Storm Christoph brought one of the wettest three-day periods on record across north Wales and north-west England. Despite new record flows on several watercourses, impact to property, whilst severe in some areas, was generally lower than expected. Some forecast rain fell as snow and as such did not reach watercourses as quickly as expected, giving time for water levels to drop before defences were overwhelmed. Active flood risk management in Greater Manchester, York and other areas significantly reduced the total number of properties flooded.

If you would like to find out more information about this event, our flood forecasting system, or our flood mapping for the UK, please fill in the form above or email our Event Response team. To ensure you are kept up to date with all future event response and company updates, subscribe to our mailing list using the form above.

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References

Daily Post. 2021 https://www.dailypost.co.uk/news/north-wales-news/it-like-scene-titanic-ruthin-19674674 [Accessed 25 Jan 2021]

Cheshire Fire Service 2021. https://www.cheshirefire.gov.uk/news-events/incidents?utm_source=Twitter&utm_medium=social&utm_campaign=Orlo [Accessed 21 Jan 2021].

Cheshire Live, 2021. https://www.cheshire-live.co.uk/news/chester-cheshire-news/mp-calls-urgent-investigation-northwich-19678950 [Acccessed 21 Jan 2021].

Denbighshire Free Press 2021 https://www.denbighshirefreepress.co.uk/news/19032661.tommys-hair-salon-clwyd-street-ruthin-lost-everything-ground-floor-flood/ [Accessed 28 Jan 2021]

Environment Agency 2021a. https://twitter.com/johncurtinEA [Accessed 22 Jan 2021]

Environment Agency 2021b. https://deframedia.blog.gov.uk/2021/01/25/guardian-coverage-of-flood-defences/ [Accessed 25 Jan 2021]

Examiner Live, 2021. https://www.examinerlive.co.uk/news/local-news/hundred-families-offered-hotel-rooms-19675940 [Accessed 21 Jan 2021].

Guardian 2021. https://www.theguardian.com/environment/2021/jan/24/england-vital-flood-defences-almost-useless [Accessed 24 Jan 2021]

Flood Warning Information Service 2021. https://flood-warning-information.service.gov.uk/warnings?location=+Manchester [Accessed 19 Jan 2021].

Manchester Evening News 2021. https://www.manchestereveningnews.co.uk/news/greater-manchester-news/didsbury-flood-evacuated-storm-christoph-19669989 [Accessed 21 Jan 2021].

Manchester Evening News 2021. https://www.manchestereveningnews.co.uk/news/uk-news/gallery/dramatic-pictures-show-people-being-19670214 [Accessed 28 Jan 2021].

Met Office 2021. https://www.metoffice.gov.uk/binaries/content/assets/metofficegovuk/pdf/weather/learn-about/uk-past-events/interesting/2021/2021_01_storm_christoph.pdf [Accessed 27 Jan 2021]

North Yorkshire Fire & Rescue Service, 2021. https://www.northyorksfire.gov.uk/news-events/breaking-news/20012021 [Accessed 21 Jan 2021].

Northwich Guardian, 2021. https://www.northwichguardian.co.uk/news/19032426.northwich-flood-defences-work-says-environment-secretary/ [Acccessed 21 Jan 2021].

South Wales Police, 2021. https://twitter.com/swpolice/status/1352624709561692161?s=20 [Accessed 21 Jan 2021].

The Standard, 2010. https://www.chesterstandard.co.uk/news/19042737.cheshire-west-leaders-call-government-support-help-storm-christoph-flooding-victims/ [Accessed 21 Jan 2021].

Wales Online 2021. https://www.walesonline.co.uk/news/wales-news/storm-christoph-bangor-dee-wrexham-19686179 [Accessed 25 Jan 2021]