Research and analysis

Solent and South Downs water situation report: May 2026 summary

Updated 11 June 2026

Applies to England

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

Solent and South Downs (SSD) had below average rainfall in May, receiving 63% (32mm) of long term average (LTA) of 52mm. Monthly mean river flows for May ranged from exceptionally low to normal across SSD. End of month groundwater levels for May ranged from notably low to notably high. Soils across SSD ended the month drier than the LTA for May. End of month reservoir stocks were below average at Ardingly Reservoir (Ouse) and at Arlington Reservoir (Cuckmere).

1. Rainfall

SSD had below average rainfall in May receiving only 63% (32mm) of LTA (52mm). The lowest monthly total rainfall was in the Test Chalk areal unit with 25mm, 46% of LTA (54mm). The Isle of Wight areal unit received the highest monthly rainfall with 36mm, 75% of LTA (48mm).

Apart from 2 May the early part of the month was mostly dry. There were showery conditions from 10 to 19 May with the highest daily rainfall total, 23.1mm, recorded on 18 May, at Plumpton (East Sussex Chalk). The remainder of the month was very warm and dry.

The April-May 2-month period has been the seventh driest April-May period on record for the SSD as a whole and the fourth driest for the Test Chalk areal unit.

In contrast, the January to May 5-month period has been the twelfth wettest on record for SSD as a whole. The 5-month total was the seventh highest on record for East Hampshire Chalk, areal unit.

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

2. Soil moisture deficit and recharge

Soil moisture deficits (SMDs) are greater than LTA for May. Soils across SSD ended the month drier than average for May.

3. 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.

Flows were notably low on the:

• River Arun at Alfoldean
• River Ouse at Goldbridge

Flows were below normal on the:

• River Adur at Sakeham
• River Cuckmere at Cowbeech
• River Medina at Blackwater
• River Wallington at North Fareham

Flows were normal on the:

• River Test at Chilbolton
• River Test at Broadlands
• River Meon at Mislingford
• River Rother at Iping Mill
• River Itchen at Allbrook and Highbridge

The monthly mean flows for May ranked the fourth lowest for the River Lymington at Brockenhurst since 1960.

4. Groundwater levels 

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

Groundwater levels were notably low at Carisbrooke Castle (Isle of Wight).

Groundwater levels were normal at:

• Lopcombe Corner (Test Chalk)
• Clanville Gate (Test Chalk)
• Harting Common (Western Rother Greensand)
• Beeding Hill (West Sussex Chalk)
• Houndean Bottom (East Sussex Chalk)
• Catherington (East Hampshire Chalk)
• Chilgrove (West Sussex Chalk)

Groundwater levels were above normal at:

• Preston Candover (East Hampshire Chalk)
• West Meon (East Hampshire Chalk)
• Cornish Farm (East Sussex Chalk)

Groundwater levels were notably high at:

• Youngwoods Copse (Isle of Wight)

The groundwater level at Carisbrooke Castle was the fifth lowest on record for May since 1977.

5. Reservoir stocks

End of month reservoir stocks were below average at Ardingly Reservoir (Ouse) and at Arlington Reservoir (Cuckmere). Ardingly Reservoir was at 95.5% of total capacity (LTA 97%) and Arlington Reservoir was at 86% of total capacity (LTA 93.2%).

6. Environmental impact 

In May there were 2 licence restrictions in force throughout the month:

• cessation of abstraction for one licence on the Loxwood Stream (Arun and Western Streams)
• restriction on abstraction rates for one licence on the River Meon (East Hampshire) which reduced to cessation later in the month

In the third week of May there were additional restrictions in Arun and Western Stream and the New Forest which remained in force until the end of the month.

No flood alerts or flood warnings were issued in May.

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.