Research and analysis

Solent and South Downs water situation report: May 2025 summary

Updated 12 June 2025

Applies to England

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

1. Summary

Solent and South Downs (SSD) had below average rainfall in May, receiving 47% (24.4mm) of the long term average (LTA of 52mm). Monthly mean river flows across SSD ranged from exceptionally low to normal. The end of month groundwater levels ranged from exceptionally low to notably high. Soils across SSD ended the month much drier than the average for May. End of month reservoir stocks were below average at Ardingly Reservoir (Ouse) and at Arlington Reservoir (Cuckmere).

2. Rainfall

SSD had below average rainfall in May, receiving 47% (24.4mm) of LTA (52mm). Rainfall distribution was similar to April with higher totals in the east when compared to the west of the area. The East Sussex Chalk areal unit received the most rainfall during May with 63% (32.1mm) of LTA (51.2mm). The lowest monthly rainfall totals were recorded in the Lymington and Hampshire Tertiaries areal units with 18mm which represents 36% of LTA. 

The highest daily totals were recorded on 11 May with 14.9mm at Ardingly (Ouse) and on 21 May with 14.3mm at Warnford (East Hampshire Chalk).

There were only 5 days with widespread rain, 11, 13, 21, 23 and 27 May. The rest of May was mostly dry.

The last 3 months has been the fourth driest March to May period on record for SSD. Only the March to May periods for 1893, 1976 and 2011 were drier. It was the second driest March to May period on record for the East Hampshire Chalk, Hampshire Tertiaries and the Test Chalk areal units. Only the March to May period for 1893 received less rainfall.

For longer time periods the running totals remains high. For the 24-month period (starting June 2023) it was the sixth highest total for SSD. For the 36-month period (starting June 2022) it was the highest total for SSD. 

All these statistics are based on records going back to 1871.

3. Soil moisture deficit and recharge

Soils across SSD ended the month much drier than the LTA for May.

4. River flows

Monthly mean river flows for May ranged from exceptionally low to normal across SSD.

Flows were exceptionally low on the:

• River Lymington at Brockenhurst
• River Arun at Alfoldean

Flows were notably low on the:

• River Wallington at North Fareham

Flows were below normal on the:

• River Meon at Mislingford
• River Rother at Iping Mill
• River Adur at Sakeham
• River Ouse at Goldbridge
• River Cuckmere at Cowbeech

Flows were normal on the:

• River Medina at Blackwater
• River Itchen at Allbrook and Highbridge
• River Test at Broadlands
• River Test at Chilbolton

The exceptionally low monthly mean flows for the River Arun at Alfoldean were the fifth lowest on record for May in a record going back to 1970.

5. Groundwater levels   

End of month groundwater levels for May ranged from exceptionally low to notably high across SSD.

Groundwater levels were exceptionally low at:

• Carisbrooke Castle (Isle of Wight)

Groundwater levels were notably low at:

• Beeding Hill (West Sussex Chalk)

Groundwater levels were below normal at:

• Houndean Bottom (East Sussex Chalk)

Groundwater levels were normal at:

• Lopcombe Corner (Test Chalk)
• Clanville Gate (Test Chalk)
• West Meon (East Hampshire Chalk)
• Catherington (East Hampshire Chalk)
• Harting Common (Western Rother Greensand)
• Chilgrove (West Sussex Chalk)
• Cornish Farm (East Sussex Chalk)

Groundwater levels were notably high at:

• Preston Candover (East Hampshire Chalk)
• Youngwoods Copse (Isle of Wight)

The notably high groundwater level at Preston Candover (East Hampshire Chalk) was the fifth highest on record for May since 1975. In contrast, the exceptionally low groundwater level at Carisbrooke Castle (Isle of Wight) was the fourth lowest for May in a record going back to 1977.

6. Reservoir stocks

End of month reservoir stocks were below average at Ardingly Reservoir (Ouse) and at Arlington Reservoir (Cuckmere).

Ardingly Reservoir (Ouse) was at 89% of total capacity (LTA 97%) and Arlington Reservoir (Cuckmere) was at 85.1% of total capacity (LTA 93.2%).

7. Environmental impact 

At the start of May there were 2 abstraction licence restrictions in force. The reduced abstraction rate restriction on the River Meon (East Hampshire) and a cessation on the Loxwood Stream (Arun and Western Streams). By the end of May there was an additional licence restriction in the Arun and Western Streams on the Pagham Rife. There were also 3 cessations on the Walkford Brook (New Forest).

Author: HydrologySSD@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.