Corporate report

Flood Forecasting Centre: annual review 2021 to 2022

Published 10 November 2022

Applies to England and Wales

This review provides a look back at the year April 2021 to March 2022 for the Flood Forecasting Centre (FFC).

The year saw:

• many named storms in quick succession during February 2022
• a number of periods of heavy and persistent rain

This meant a busy time operationally for the FFC.

It highlighted the role the FFC plays in flood resilience and response across England and Wales.

1. Overview for 2021 to 2022

The main features of the year were:

• flood risk generally remained very low through April and May - a few very isolated surface water flood impacts occurring during the latter half of May

• from June to September thunderstorm activity caused some surface water flooding and localised river flooding across England and Wales

• mid-June saw heavy showers and thunderstorms, followed by some prolonged thundery rain - spread northwards from the near continent

• July saw further thunderstorms and significant surface water flooding in London and Peterborough

• Storm Evert crossed the country on 30 July bringing widespread minor surface water impacts to the Midlands and the east of England

• the unsettled weather continued into August with further heavy showers bringing sporadic instances of minor impacts across the country

• several spells of heavy rain during October and early November led to instances of minor flooding across parts of England and Wales

• a notable event through this period was the prolonged heavy rain on 27 and 28 October - this brought significant river and surface water flooding to north-west England

• in late November Storm Arwen bought a few minor coastal flooding impacts

• December saw Storm Barra cause minor coastal impacts in southern England and minor surface water impacts in parts of England and Wales

• the most widespread flooding of the year period was during February - this saw 3 named storms within a week - Dudley, Eunice, and Franklin, with the latter 2 bringing most flooding impacts

• Storm Franklin brought the most rain along with some snowmelt - this resulted in significant river flooding in parts of Manchester and Yorkshire at first, and then along parts of the river Severn

The table shows the highest forecast flood risk from all flood sources for any Flood Guidance Statement (FGS) issued for each calendar day for 2021 to 2022.

Month 2021/22	Green	Yellow	Amber	Red
April	30	0	0	0
May	31	0	0	0
June	21	9	0	0
July	15	16	0	0
August	21	10	0	0
September	21	9	0	0
October	15	14	2	0
November	24	6	0	0
December	27	4	0	0
January	28	3	0	0
February	12	10	6	0
March	31	0	0	0

2. Main Flood Events

2.1 Thunderstorms and surface water flooding across London 12 July and 25 July

On 12 and 25 July, large parts of London were hit by intense storms. This resulted in the flooding of many homes and businesses as well as schools, hospitals and underground stations.

The Met Office records show that the rainfall on both days was exceptional, with a month’s rain falling in:

• an hour on 12 July
• 2 hours on 25 July

12 July flooding

Ahead of the 12 July thunderstorms the FGS highlighted:

• at day 5 (8 July), a small area of low likelihood of minor river and surface water impacts around Greater London, East Anglia and Kent

• at day 4 (9 July), a larger area of low likelihood of minor river and surface water impacts across much of eastern England including Greater London

• at day 3 (10 July), the area of low likelihood of minor impacts was highlighting northern England and north Wales

• at day 2 (11 July), an area of very low likelihood of significant surface water and river flooding impacts across parts of the south and south-east of England including Greater London

• the FGS issued on 12 July highlighted a low likelihood of significant impacts across the south and south-east of England

On 12 July, more than a month’s worth of rain fell in under an hour. Some areas received nearly 80mm of rain (170% of July’s average rainfall) over the course of the storm. Kensington, Westminster and Hammersmith were the most affected.

25 July flooding

Ahead of the 25 July thunderstorms the FGS highlighted:

• at day 4 (22 July), a very low likelihood of significant river and surface water impacts across much of England and Wales on 24 and 25 July

• at day 3 (23 July), a very low likelihood of significant river and surface water impacts across parts of the south and south-east of England on 24 and 25 July

• at day 2 (24 July), a low likelihood of significant river and surface water impacts across parts of the south and south-east of England on 24 July

• also at day 2, an area of low likelihood of significant river and surface water impacts across south-east England, including Greater London, within a broader area of very low likelihood impacts on 25 July

• on 25 July, the FGS continued to highlight an area of low likelihood of significant river and surface water impacts across south-east England, including Greater London

The floods from these events caused major disruption. It is estimated that flooding by storm water or sewage overflow affected:

• more than 1,000 properties - including homes, businesses and schools (the majority of these from the 12 July storm)
• more than 30 underground stations
• some hospital wards, which had to be evacuated

2.2 Heavy and persistent rain, 26 to 31 October

The beginning of October started unsettled, with river catchments sensitive. A slow-moving frontal system then brought persistent rain across parts of northern England from the 26 to 29 October.

The highest rainfall accumulations were seen across the Lake District, Cumbria. Here, over 400mm of rain fell in the last 6 days of the month.

On October 27, 2 rain-gauges recorded daily totals of over 200mm in an event known as a ‘warm-conveyor.’ This is where rainfall is greatly increased across high ground.

This event was very similar in characteristics to the extreme rainfall events of December 2015 and November 2009. These brought serious flooding to northern England.

Ahead of this event the FGS highlighted:

• river and surface water impacts at day 5 (23 October) with a very low likelihood
• the forecast impact level was increased at day 3 (25 October), to a very low likelihood of significant impacts
• 27 October saw the forecast likelihood increase to a medium flood risk (amber) - flagging a high likelihood of significant surface water impacts and a medium likelihood of significant river flooding impacts across Cumbria
• river flooding was forecast to continue at least until the 29 October

The persistent heavy rainfall brought significant flooding impacts across the English Lake District. These included:

• around 40 properties flooded (but over 1200 protected by flood defences)
• significant travel disruption with roads flooded and cars stranded
• rail passengers asked to avoid the West Coast main line and Cumbria coastal routes

2.3 Storms Dudley, Eunice and Franklin 16 to 21 February

In February 2022 the United Kingdom experienced 3 named storms (Dudley, Eunice and Franklin) in one week for the first time ever. These resulted in:

• high spring tides, a large storm surge and large waves on the coast

• a risk of severe flooding to south-west England and the entire Welsh coastline

Following a wet start to the month, the successive storms, together with snow at higher levels, brought significant flooding to parts of England and Wales.

Fortunately, severe coastal flooding in the Bristol Channel and Severn Estuary was avoided as defences held, and the storm surge did not coincide with high tide.

372 properties were flooded during the events. However, flood protection schemes and responses protected approximately 50,000 properties.

February 2022 set a number of national benchmarks:

• 3 named storms within a week, a first since UK storm naming began in 2015/2016

• record high river levels were reached at some local sites on the Lower Don, Wharfe, Severn, Mersey and Derwent (Derbyshire)

• for the first time severe coastal flood risks were flagged for the whole Welsh coastline and south-west of England

Storm Eunice

Ahead of Storm Eunice on the 18 February the FGS highlighted:

• coastal impacts at day 5 (14 February) with a very low likelihood of significant coastal flooding around the coasts of Wales and south-west of England

• the forecast impact level was increased on day 4 (15 February) to a very low likelihood of severe impacts for the coasts of Wales and south-west England

• Day 3 (17 February) saw the forecast likelihood for 18 February increase to a medium flood risk (amber) - a low likelihood of severe impacts was flagged around the whole coast of Wales and down to Cornwall

Fortunately, the morning of 18 February saw the peak storm surge arrive an hour or two after the high tides meaning impacts were very limited.

Storm Franklin

Ahead of Storm Franklin on the 20 to 21 February the FGS highlighted:

• at Day 4 (17 February), a small area with a medium likelihood of minor river and surface water flooding impacts around Greater Manchester - a larger area with a low likelihood of minor impacts was highlighted across east Wales and north-west England

• at Day 3 (18 February), very low likelihood of significant impacts across the Greater Manchester area as well as parts of the Midlands for Sunday - a medium likelihood of minor impacts was shown in north-west England and Powys, Shropshire, Herefordshire

• at Day 2 (19 February), the forecast for the Sunday increased the risk for Greater Manchester (River Mersey catchment) to a very low likelihood of severe impacts, with the river risk lasting until Wednesday

• the FGS issued on Day 1 (20 February) increased the overall flood risk to medium (amber) in the River Mersey catchment (a low likelihood of severe impacts) and western parts of North Yorkshire (a medium likelihood of significant impacts) - river flooding was now considered possible until Thursday on the Rivers Severn, Trent and Ouse

Significant river flooding impacts were observed across parts of:

• North, South and West Yorkshire
• Derbyshire
• Cheshire
• Greater Manchester

Widespread minor impacts from surface water and river flooding were recorded:

• from South Wales through the Severn catchment
• across north-west and north-east England up to Cumbria and County Durham

Impacts on the larger rivers, particularly the River Severn lasted until Saturday 26 February.

3. Customer insight

Key engagement activities this year are as follows:

• completing the transition of the FFC website to the GOV.UK platform (with the help of the Defra Digital team)

• successfully launching the new Flood Outlook product along with supporting materials and training

• continuing to develop the FFC user group

• carrying out winter readiness training

• measuring our user satisfaction through the biannual responder survey

• supporting development of the new strategic plan by providing user insight

• delivering a review of all user training and implementing improvements and additional support across the suite of materials available

4. Service development and improvement

4.1 Improving flood forecasting production with the new Incident Management Forecast System (IMFS)

We launched our new hydromet service for the Environment Agency on their new IMFS on 14 April 2021.

This service provides enhanced forecast scenarios for England to the Environment Agency, supporting their local flood forecast and warning service.

4.2 Introduction of a new groundwater flood forecasting service

We commissioned a new groundwater flood forecasting service to inform our FGS groundwater flood risk assessments. This was launched in November 2021 and:

• improves our capability in this area, through a partnership with British Geological Survey
• provides operational groundwater forecasts from November to April (the period of the year during which the potential for groundwater flooding is raised)

Through partnering with the British Geological Survey we now have access to:

• to a web-based forecasting tool
• consultancy support providing expertise in groundwater modelling and forecasting

4.3 Improving the value of our 6 to 30 day Flood Outlook service

Following on from preparatory work last year, we continued with the development of the new Flood Outlook service. Informed by our users, the refreshed Flood Outlook went live in spring 2022 with:

• improved content and a new design
• new training videos to support users to get the most from the product

4.4 Hydromet service continuity for Natural Resources Wales (NRW)

New production and delivery arrangements were implemented in March 2022 to ensure continued provision of Hydromet Services for NRW. This was necessary because of the retirement of an old legacy IT system.

We aim to continue to work closely NRW to improve the design, delivery and value of this service over the coming years.

4.5 Multi Model Decider – improving our medium to long-range flood risk forecasting

Decider is a medium to long-term weather forecast tool developed by the Met Office.

For several years the FFC have worked closely with Met Office colleagues to tailor this tool. It supports our coastal and river flood risk assessments, particularly for the Flood Outlook service.

Continuing this collaboration, this year we supported the development of a new ‘multi-model’ ensemble based version of Decider. It is designed to:

• improve our flood risk assessment for the 6 to 30 day ahead period
• aid early identification of the potential for extreme events

The new multi-model version of Decider will be implemented during routine upgrade windows through summer 2022.

4.6 Flood Guidance Statement lifecycle – improvements for verification

The FFC has always recognised the importance of reviewing how well our FGS performs in providing flood risk guidance over the 5 day horizon. To support this, we operate a verification system that collates forecast and observation data and analyses the accuracy of our guidance.

This year we developed a new resilient and supported verification system to replace an aging software.

This type of replacement work is critical for the FFC to remain fit for the future in an environment where technology is advancing at an increasing rapid rate.

5. Conclusion

If you have any questions about our performance during this year, please email us at ffcenquiries@environment-agency.gov.uk.