Research and analysis

South-east England water situation report: October 2024 summary

Updated 13 November 2024

Applies to England

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

1. Summary

The south-east of England received 119% of the long term average (LTA) rainfall for October. The highest daily rainfall was 41.5 mm, recorded at Rapsgate (Thames, THM) on 8 October. Soil moisture deficits (SMDs) decreased significantly due to rainfall in the first half of the month, resulting in most areal units in THM and Solent and South Downs (SSD) ending the month at or near zero. River flows responded accordingly, with several sites recording their highest October flows on record. A total of 65 fluvial flood alerts and 3 flood warnings were issued throughout the month. Groundwater levels increased due to the substantial rainfall in the last 12 months, with several sites recording their highest levels since records began. Reservoir stocks remained above average at most reservoirs across the south-east, with just 2 exceptions.

2. Rainfall

The south-east of England received 119% of the LTA rainfall for October. The month was a tale of two halves. The first half of the month was characterised by unsettled weather, accounting for an average of 75% of the monthly total rainfall across the region. The second half was dominated by high-pressure systems, leading to more settled and drier conditions. On average, there were 11 dry days (days with less than 0.2 mm of rainfall) during October across the south-east.

The highest daily rainfall total was 41.5 mm recorded at Rapsgate (THM) on 8 October. This date also produced some of the top 5 highest rainfall totals for the month in Kent and South London (KSL) and SSD. In contrast, Hertfordshire and North London (HNL) experienced its highest rainfall totals on 1 October.

While October’s rainfall was generally unremarkable, the statistics for the 12 months ending in October are noteworthy. THM experienced its wettest 12 months on record. The south-east region recorded its second wettest 12 months ending in October since 2001. HNL had its wettest year since 2001, ranking as the fourth wettest overall, and KSL had its wettest year since 2014, ranking fifth overall.

3. Soil moisture deficit and recharge

In October, SMDs across the south-east decreased rapidly in response to rainfall during the first half of the month. By the end of the month, most areal units THM had SMDs at or near zero. Similarly, SMDs in Chilterns East and Lee Chalk (HNL) fell to near zero.

In SSD, all areal units recorded SMDs at or close to zero by the end of the month. Meanwhile, KSL, being drier than the other south-eastern Areas had only 2 out of 5 areal units with SMDs near zero by the end of October.

There has been significant recharge during the month, particularly after the rainfall in early October. This was due to the SMDs returning to zero earlier than is usually expected in the hydrological winter (October to March). There was over two and a half times the average recharge across the south-east by the end of the month. Effective rainfall totals were significantly above the LTA, with THM recording 452% of the LTA and SSD recording 254% of the LTA. In contrast, towards the east, HNL recorded 162% of the LTA and KSL experienced the least recharge, with effective rainfall at 154% of the LTA.

4. River flows

In October, key indicator flow sites displayed a range of responses. Rivers affected by the rainfall on 8 October responded very quickly, including normally slower responding groundwater-fed rivers that were already high by the end of September.

Of the 21 indicator flow sites across the south-east of England, the monthly mean flows for 8 sites were in the exceptionally high category during October. Rivers which were exceptionally high were mainly in THM and HNL and included:

• The Thames at Farmoor (THM)
• The Mimram at Panshanger (HNL)
• The Kennet at Marlborough (THM)

The highest October flows on record were recorded at the:

• Coln at Bibury (THM), with the previous second-highest flow in 2012
• Thames at Farmoor (THM), surpassing the second-highest flow recorded in 2019
• Kennet at Marlborough (THM), exceeding the second-highest flow from 2012
• Ver at Colney Street (HNL), with the previous second-highest flow in 2001
• Mimram at Panshanger (HNL), with the second-highest flow in 1993

Additionally, the Loddon at Sheepbridge (THM) recorded its second-highest October flow since 1987. The Thames at Kingston (THM) recorded its fourth-highest October flow with the third highest flow in 1960, the second-highest flow in 1891 and the highest ever in 1903.

Overall, the October flows across the south-east reflected response to the rainfall during the month, with several rivers recording their highest flows in decades. A total of 65 fluvial flood alerts and 3 fluvial flood warnings were issued during October.

Warning type	HNL	THM	SSD	KSL	Total
Fluvial flood alerts	6	26	12	21	65
Fluvial flood warnings	0	0	3	0	3
Total	6	26	15	21	68

5. Groundwater levels   

In October, groundwater levels increased across most sites, driven by the substantial rainfall during the last 12 months. Sites across KSL were the exception to this where all the indicator sites continued to fall throughout October. Of the 16 indicator sites, almost half the sites ended the month at exceptionally high levels during the month, they were all in THM, HNL and SSD. These were:

• Rockley, Stonor Estate, Tile Barn Farm (all THM), Lilley Bottom (HNL), and Clanville Gate (SSD) all recorded their highest groundwater levels for October since records began

• Ampney Crucis  and Gibbet Cottages (both THM) ranked second, with the highest levels since 2019 and 2007, respectively

• Ashley Green (HNL) and West Meon (SSD) ranked third, with the highest levels since 2001 and 2021, respectively

• Lopcombe Corner (SSD) recorded its second-highest groundwater level for October since 1966

6. Reservoir stocks

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