Research and analysis

South-east England water situation report: December 2025 summary

Updated 14 January 2026

Applies to England

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

1. Summary

December was another month when around the long term average (LTA) rainfall was recorded across the south-east of England. There was 105% of the monthly LTA rainfall recorded, with around 20% of the monthly totals measured on 18 December. The western halves of Thames (THM) and Solent and South Downs (SSD) experienced rainfall in the above normal category for December while the rest of the south east had rainfall in the normal category. The soil moisture deficits (SMDs) fell during the month, particularly after the rainfall on 18 December, but rose slightly during the dry week at the end of the month to end generally above the LTA for December. Recharge reflected the distribution of rainfall and SMDs. Where the SMDs were very low, there was significant recharge.

Hydrographs for most of the key flow indicator sites responded strongly to the rainfall on December 18, then fell in response to the dry weather towards the end of the month. All 16 indicator sites were in the normal or above, category for December. There were 98 fluvial flood alerts and 15 fluvial flood warnings issued during the month. Groundwater levels at 14 of the indicator sites rose during December, with significant rises at responsive sites on the south coast. The majority of the key indicator sites recorded levels in the normal range for the month. The reservoir stocks have all risen across the south east.

2. Rainfall

December was another month when around the LTA rainfall was recorded across the south east. There was 105% of the monthly LTA rainfall recorded. December began quite wet with over 50% of the monthly total on average, in the first 8 days. The wettest day was 18 December when around 20% of the monthly total was recorded. The top 5 daily rainfall totals were measured on 18 December, all in SSD with the highest daily total of 37.2mm recorded at Petersfield, Western Rother Greensand. All top 5 totals were greater than 30mm. Both Hertfordshire and North London (HNL) and Kent and South London (KSL) recorded their highest daily totals on 18 December, albeit a little less than SSD with 24mm and 30mm respectively. The highest daily total for THM was 33.9mm, recorded at Rapsgate, Cotswolds West on 15 December when a band of heavy rainfall clipped the top of the Thames catchment and the western half of SSD.

The western halves of THM and SSD experienced rainfall in the above normal category for December while the rest of the south east had rainfall in the normal category. On average there were 14 ‘dry’ days (less than 0.2mm rainfall in a day). These were largely in the second and last week of the month. The year ended with a particularly dry and cold snap across the south east, with a dusting of snow overnight on 30 December.

3. Soil moisture deficit and recharge

The SMDs fell during the month, particularly after the wet start to the month and rainfall on 18 December, but rose slightly during the dry week at the end of the month to be generally above the LTA for December. The SMDs for areal units towards the west fell to zero and remained close to zero during the month. However, the drier east still had significant SMDs at the end of December.

Recharge reflected the distribution of rainfall and SMDs. Where the SMDs were very low, there was significant recharge, for example Test Chalk and the Isle of Wight (both SSD) and the Cotswolds (THM). The recharge for SSD on average was greater than the LTA for December. By contrast, the average recharge for HNL was only 13%.

4. River flows

Unsurprisingly, hydrographs for most of the key flow indicator sites responded to the wet weather at the beginning of the month and strongly to the rainfall on December 18. Flows then fell in response to the dry weather towards the end of the month. This was particularly the case for the sites on the River Thames (THM) and rivers draining impermeable catchments, for example Lymington River at Brockenhurst (SSD) and the Medway at Teston and East Farleigh (KSL). All 16 indicator sites were in the normal or above category for December. Four sites were at notably high flows, including the Arun at Alfoldean (SSD) which had the fourth highest December flow on record, the highest since 2019. There were 98 flood alerts and 15 flood warnings issued during the month.

5. Groundwater levels   

Groundwater levels at 14 of the indicator sites rose during December. The exceptions were Stonor (Chilterns, THM) and Lilley Bottom (HNL) where levels continued to fall. Responsive boreholes on the south coast in SSD had the largest groundwater rises with Chilgrove levels rising by 22m and Houndean by 12m since November. The majority of the sites recorded levels in the normal range for the month. The 3 exceptions were Jackaments (THM) where levels were above normal; Sweeps Lane (KSL) with below normal levels and Chipstead (KSL) with exceptionally low levels. Chipstead had the third lowest level on record (started in 2002) and was the lowest level since 2011.

6. Reservoir stocks

The reservoir stocks have all risen across the south-east of England. However, stocks remained below average for December at all reservoirs except Farmoor (THM), Bough Beech (KSL) and Weir Wood (KSL) which ended the month above the LTA and Lower Lee (HNL) and Powdermill (KSL) which were both average for December.

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.