Research and analysis

South-east England water situation report: March 2025 summary

Updated 14 April 2025

Applies to England

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

1. Summary

March was a dry month with only 12% of the long term average (LTA) rainfall recorded across the south-east of England. There were 23 ‘dry’ (less than 0.2mm rainfall) days during the month which meant that it was the driest March since 1961 for the south-east of England and all 4 Areas. Soil moisture deficits (SMDs) increased throughout the month and ended March at 3 times the LTA. The combination of such low rainfall and high SMDs meant that there was zero recharge during March. For the winter as a whole (October to March), there was 127% of the LTA recharge, which was the third consecutive winter when above average recharge was recorded.  River flows fell at all of the key indicator sites across the south-east of England and ranged from exceptionally high down to notably low during March. Groundwater levels at most of the key indicator sites fell during the month. By the end of March, groundwater levels ranged from exceptionally high in the Lee Chalk (Hertfordshire and North London, HNL) and Chilterns (Thames, THM) to notably low in the faster responding Oolites in THM.

2. Rainfall

March was a dry month with only 12% of the LTA rainfall recorded across the south-east of England. The rainfall was consistent across all Areas that recorded 12% LTA except THM that recorded 11%. The highest daily total was 10.8mm on 22 March at Aylesbury (THM).  The wettest day was 3 March when the top 5 daily rainfall totals in Solent and South Downs (SSD), Kent and South London (KSL) and THM (with the exception of Aylesbury on 22 March) were recorded. Just over a quarter of the monthly rainfall total fell on this day. There were 23 ‘dry’ (less than 0.2mm rainfall) days during the month, that meant it was the driest March since 1961 for the south-east of England, all four Areas and around a third of the areal units. It has also been the driest March since 1990 for another third of the areal units.

3. Soil moisture deficit and recharge

SMDs increased throughout the month, with a small exception around 23 March when it rained. SMDs ended the month at 3 times the LTA for the end of March.  This was the first time that SMDs were above average since August 2024. The combination of such low rainfall and high SMDs meant that there was zero recharge during March.  For the winter as a whole (October to March), there was 127% of the LTA recharge, which was the third consecutive winter when above average recharge was recorded.

4. River flows

River flows fell at all of the key indicator sites across the south-east of England. Flows ranged from exceptionally high to notably low during March. Generally, flows fell more steeply and to lower flows than have been seen for quite some time across the clay catchments across the Weald in KSL. Rivers in the chalk, groundwater-fed catchments were maintained at higher and more steady flows by the high groundwater levels. The Mimram at Panshanger and the Ver at Colney Street (both HNL) were the fourth and sixth highest March flows, respectively. This is the second consecutive year that both these rivers have been at their highest March flows. Just one fluvial flood alert was issued in KSL.

5. Groundwater levels   

The low rainfall totals, coupled with climbing SMDs and the lack of recharge has meant that groundwater levels at most of the key indicator sites fell during March. A couple of sites (Chipstead, KSL and Ashley Green, HNL) levelled off and there were a number of sites that continued to rise. The sites that rose included the slower responding chalk at Stonor (THM) and several sites in KSL including Riddles Lane in the North Kent Chalk. By the end of March, groundwater levels ranged from exceptionally high in the Lee Chalk (HNL) and Chilterns (THM) to notably low in the faster responding Oolites in THM. Lilley Bottom (HNL) remained exceptionally high and was the second highest March level on record. There were 6 groundwater alerts still in force, across THM, SSD and HNL.

6. Reservoir stocks

Farmoor and most of the reservoirs in KSL ended the month above the LTA. Only Lower Thames (THM) and Darwell (KSL) were below the LTA. The Lee Valley (HNL) and Arlington and Ardingly (SSD) reservoirs all ended March at the 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.