Research and analysis

South-east England water situation report: November 2024 summary

Updated 13 December 2024

Applies to England

• Publication for Northern Ireland
• Publication for Scotland
• Publication for Wales

1. Summary

November was a month of two contrasting halves across the south-east of England. The month started by being dominated by high pressure with dull, dry and mild conditions, described by the Meteorological Office as ‘anticyclonic gloom’. Then there was cold weather and patchy light snowfall on 21 November and 2 named storms a few days later. Despite these storms, the south-east of England received only 107% of the long term average (LTA) monthly rainfall. The soil moisture deficits (SMDs) rose slightly in the first half of the month owing to the dry weather. The SMDs ended the month below the LTA at zero or close to zero for most areal rainfall units in Thames (THM), Solent and South Downs (SSD) and Hertfordshire and North London (HNL). Recharge across the south-east of England was significantly higher than the LTA during the month, particularly in THM. The groundwater-fed rivers displayed at least notably high flows towards the north and west. On the Wealdon Clay in Kent, rivers remained in the normal range for the month. There were 108 fluvial flood alerts and 54 fluvial flood warnings issued in November. The cumulative impact of the last 12 months’ rainfall across the south-east of England has been particularly reflected by the high groundwater levels during November.

2. Rainfall

November was a month of 2 contrasting halves across the south-east of England. The month started by being dominated by high pressure with dull, dry and mild conditions, described by the Meteorological Office as ‘anticyclonic gloom’. Then there was cold weather and patchy light snowfall on 21 November and 2 named storms a few days later. The first storm was Bert on 23 and 24 of the month which brought widespread heavy rainfall and strong winds. The second was Storm Conell which resulted in heavy rainfall to the south coast on 26 November. Despite these storms, the south-east of England received only 107% of the LTA monthly rainfall. The wettest area was THM which received 137% of the rainfall LTA for November. Kent and South London (KSL) was the driest and only recorded 87% of the LTA for the month.

The first half of the month accounted for an average of 9% of the monthly total rainfall. The dates of the highest rainfall totals were 24 and 26 November, coinciding with the 2 storms. The highest daily total was 47.8mm recorded at Grimsbury, THM on 24 November. Calbourne, SSD recorded 45.7mm on 26 November.

3. Soil moisture deficit and recharge

The SMDs rose slightly in the first half of the month owing to the dry weather. However, these were reduced significantly after rainfall on 18 November, followed by a reduction to zero after Storm Bert. The SMDs ended the month at zero or close to zero for most areal rainfall units in THM, SSD and HNL. This was significantly below the LTA for November. Some residual deficits remained in KSL which has been significantly drier than the other 3 areas. As there has been a wet start to the winter, with corresponding low SMDs, the recharge across the south-east of England was significantly higher than the LTA during the month, particularly in the west. In THM there was almost 3 times the amount of recharge that we would normally expect for this time of year. The last time THM had this level of recharge for October and November was in 2000.

4. River flows

There was some contrast in the response of the indicator flow sites during the month. The groundwater-fed rivers displayed at least notably high flows towards the north and west. The groundwater components of their flows have been supported by the high recharge during the last 3 months. These rivers responded quickly to the rainfall but returned to their high baseflows prior to the storms. Examples included:

• Mimram at Panshanger (HNL) which recorded the highest November flows on record
• Ver at Colney Street (HNL) which also recorded the highest November flows on record
• Kennet at Marlborough (THM) which recorded the fourth highest November flows - the November flows in 2023 were the highest on record

On the Wealdon Clay in Kent, rivers remained in the normal range for the month. Further to the wetter west the rivers draining permeable catchments recorded flows in the above normal or notably high category. Generally, these quicker responding catchments responded rapidly and strongly to the heavy rainfall on 24 and 26 November, then flows dropped away quickly These included

• Loddon at Sheepbridge (THM)
• Lymington at Brockenhurst (SSD)
• Arun at Alfoldean (SSD)
• Medway at Teston and East Farleigh (KSL)
• Teise at Stonebridge (KSL)

There were 108 fluvial flood alerts and 54 fluvial flood warnings issued in November.

5. Groundwater levels   

The cumulative impact of the last 12 months’ rainfall across the south-east of England has been particularly reflected by the high groundwater levels during November. The highest levels were recorded in the Chilterns (HNL and THM), Berkshire Downs (THM) and the Test Chalk (SSD) during the month. The following sites recorded their highest November levels on record;

• Ampney Crucis, Cotswolds (THM)
• Stonor Estate, Chilterns (THM)
• Lilley Bottom, Chilterns (HNL)

Indicator sites on the North and South Downs were mainly in the above normal category. Groundwater levels rose at 10 of the 16 indicator sites across the south-east and were at notably high or higher at 8 sites.

6. Reservoir stocks

The reservoirs remained above average for November at all of the reservoirs across the south-east with 2 exceptions. Storage at Arlington (SSD) and Bewl (KSL) ended the month below the monthly LTA.

Author: groundwaterhydrology@environment-agency.gov.uk     

All data are provisional and may be subject to revision. The views expressed in this document are not necessarily those of the Environment Agency. Its officers, servants or agents accept no liability for any loss or damage arising from the interpretation or use of the information, or reliance upon views contained in this report.