Research and analysis

South-east England water situation report: September 2026 summary

Updated 14 October 2026

Applies to England

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

1. Summary

September was another warm and dry month, with only 61% of the long term average (LTA) monthly rainfall recorded across the south-east of England. Three-quarters of the monthly total was recorded in the first 13 days after which, the weather resumed the warm and dry characteristics common during the summer. Six of the last seven months have had below the LTA rainfall, after a particularly wet January and February. It has been the driest three-month period ending in September on record for the south-east of England, Hertfordshire and North London (HNL) and Thames areas (THM). September marks the end of the hydrological summer period when the south-east received only 54% of the expected summer rainfall this year.

The soil moisture deficits (SMD) rose steadily during the month to end the month around twice the LTA. There was little recharge during September. Seasonal declines continued in the indicator sites for both flow and groundwater levels after the continued dry conditions. No fluvial flood alerts were issued.

2. Rainfall

September was another warm and dry month, with only 61% of the LTA monthly rainfall recorded across the south-east of England. The wettest days were the 7 and 8 of the month, which together accounted for more than half of the monthly total. Three-quarters of the monthly total was recorded in the first 13 days after which, the weather resumed the warm and dry characteristics common during the summer. The 7 and 8 September provided the highest daily totals for all four areas in the south east. The highest daily rainfall total was 22.9mm, recorded at Wroxall on the Isle of Wight, Solent and South Downs (SSD) on 7 September. On average, there were 7 ‘wet’ days, where the daily total across the south-east was greater than 1mm during the month, mainly in the first half of the month.

Six of the last 7 months have had below the LTA rainfall, after a particularly wet January and February. It has been the driest three-month period ending in September on record for the south-east, HNL and THM areas. A large number of their component hydrological areas also recorded the driest 3-month period, particularly towards the north. This is reflected in the exceptionally low category on the map showing 3 months in Section 2.1 of the full report. A similar pattern is apparent in the map for 6 months ending September, which was the driest on record for both HNL and THM.

September marks the end of the hydrological summer period when the south-east received only 54% of the expected summer rainfall. It is also the end of the hydrological year when the south-east received just less than the LTA rainfall at 93%.

3. Soil moisture deficit and recharge

The SMDs rose steadily during the month, with slight reductions around the 7 and 8 September after the rainfall, to end the month around twice the LTA. Most hydrological units had the highest SMD on record for the end of September, some being significantly higher than the second placed year. Unsurprisingly, there was little recharge during September and during the summer only 20% of the LTA recharge was calculated across the south-east.

4. River flows

The seasonal recession continued during the month at all 21 flow indicator sites. As there were record breaking high SMDs across the south-east, there was very little response to the rainfall in the flows. Around half of the sites had flows in the normal band. These were largely rivers draining chalk catchments, supported by groundwater baseflows, including the River Mimram at Panshanger (HNL) and the River Dour at Crabble Mill (Kent, South London and East Sussex, KSLES). The remaining 11 flow indicator sites were evenly split between the three categories from below normal to exceptionally low. The 3 rivers in the exceptionally low category included the River Coln at Bibury (THM) and the River Lymington at Brockenhurst (SSD). The River Thames at Farmoor (THM) and the River Arun at Alfoldean (SSD) both had the third lowest September flows on record. No fluvial flood alerts were issued during the month.

5. Groundwater levels   

All 16 of the groundwater indicator sites showed declining levels during September. Seven of the sites were in the normal range for the month, scattered across the Chilterns, Test Chalk and North Downs. There were 2 boreholes with levels in the exceptionally low range. These were Chipstead, North Downs (KSLES) and Carisbrooke Castle, Isle of Wight (SSD).  Carisbrooke had the lowest levels since September 1989 and Chipstead were the lowest since September 2006. The oolites at Jackaments (THM) had levels in the notably low range and the rate of decline was less steep during the month.

6. Reservoir stocks

The warm temperatures and below average rainfall has resulted in the continued decline in reservoir storage across the south-east. All of the reservoirs recorded below LTA storage for September with one exception being Weir Wood (KSLES) which ended the month above the LTA.

Most of the water companies that operate across the south-east have now issued temporary use bans (TUBs) as a result of the dry conditions of the last couple of months.

The West Berkshire Groundwater Scheme (THM) has been operated during the month in order to supplement the flows in the River Thames and to bolster the water available for abstraction in the Lower Thames.

Author: HNL Groundwater and Hydrology, 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.