Research and analysis

Hertfordshire and North London water situation: February 2026 summary

Updated 12 March 2026

Applies to England

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

1. Summary

Similar to January, February was a month that brought heavy rainfall across the Hertfordshire and North London area (the Area), with 91mm of rain (188% of the long term average (LTA)) received. Soil moisture deficits (SMD) remained at zero throughout the month, which meant that effective rainfall was well above average for the time of year. River baseflows increased further during February, with most chalk river indicator sites recording mean flows in the above normal band. Due to the month’s consistent rainfall, most clay and urban indicator sites recorded month mean river flows in the notably high band. Groundwater levels increased at all indicator sites during February, with most sites recording end of month levels in the normal band.

2. Rainfall

February was another month that brought heavy rainfall across the Hertfordshire and the Area, with a rainfall total of 91mm, equivalent to 188% of the LTA. All rainfall units ended the month in the notably high band, with the exception of the Lower Lee unit, which was in the exceptionally high band. Additionally, over the last 3 months, rainfall totals in all areal units fell into the exceptionally high band, apart from the Roding, which ended the period in the notably high band. There was a very consistent distribution of rain across February, with only 3 dry days (days when less than 0.2mm of rain was recorded). The highest rainfall total was on 5 February, with 21.9mm recorded at Mill Green STW (Lee Chalk unit). Other high rainfall totals were mostly recorded in the north of the Area, including:

• 21.2mm at North Mymms (North London unit)
• 18.2mm at Radlett STW (Chilterns East Colne unit)
• 18.0mm at Stevenage (Lee Chalk unit)

3. Soil moisture deficit and recharge

The consistent rainfall that the Area received during February allowed soil moisture deficits to remain around zero throughout the month (below the LTA). This allowed for a significant amount of effective rainfall to be recorded for the time of year, reaching 266% of the LTA. This level of effective rainfall should allow for a continued recharge of groundwater levels at least until the end of March.

4. River flows

River baseflows increased from January’s levels during February, with most chalk indicator sites recording month mean flows in the above normal band. Denham (River Colne) and Howe Green (River Lee) were the 2 exceptions, which recorded month mean flows in the notably high and exceptionally high bands respectively. In the clay and urban catchments, meanwhile, all indicator sites recorded month mean flows in the notably high band, apart from Redbridge (River Roding), which finished February in the exceptionally high band. High monthly flows in these areas were helped by the month’s heavy rainfall, with the most significant flow peaks occurring around 6 and 15 February. During February, a total of 21 flood alerts were issued across the area at various points during the month. Despite all the alerts, no flood warnings were issued.

5. Groundwater levels

During February, groundwater levels increased at all indicator sites in the Area, helped again by the recent effective rainfall. In the Mid-Chilterns Chalk aquifer, all indicator sites ended the month in the normal band. The Upper Lee Chalk aquifer, however, saw more of a mix of bandings, with Lilley Bottom and Therfield Rectory in the normal band, and Crescent Cottages and Hixham Hall in the above normal band. Cave Gate was the only indicator site in the Area to record its end of month groundwater level in the notably high band.

6. Reservoir stocks

During February, reservoir stocks in the Lee Valley group started the month at 88% of live capacity and ended the month at 92%, slightly above the average level for the time of year. In the Lower Thames group, reservoir stocks started February at 89% of live capacity and ended the month at 90%, meaning it was below its average level.

7. Environmental impact 

In the Colne catchment, February generally saw chalk river sources moving upstream of where they were in January, the:

• River Ver was flowing downstream of Markyate and flowed for its entire length
• River Gade started flowing at Bradden Lane.
• source of the River Bulbourne moved upstream to the fields above Dudswell
• source of the River Chess moved further upstream of Chesham to Missenden Road
• River Misbourne was flowing upstream of Great Missenden

The chalk river sources in the Upper Lee generally flowed from similar locations to where they were in January, the:

• source of the River Mimram moved upstream of Whitwell Gas Compound
• River Beane flowed upstream of Newall Lane, but temporarily ran dry in Cromer
• source of the River Rib was upstream of Reed End, where it flowed intermittently before gaining a steadier flow downstream of Chipping
• River Ash (Herts) flowed intermittently from Meesden, gaining a steadier flow at Little Hadham
• River Stort still flowed from its source above Langley Lower Green

To protect the environment, during February a number of abstraction licence flow constraints were in force. This ranged between 3 and 4 per week, out of a month maximum of 49.

Author: Groundwater and Hydrology, groundwaterhydrology@environment-agency.gov.uk

Contact Details: 03708 506 506

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 within.