Solent and South Downs water situation report: December 2024 summary
Updated 14 January 2025
Applies to England
© Crown copyright 2025
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1. Summary
Solent and South Downs (SSD) had below average rainfall in December, receiving 66% (59mm) of the long term average (LTA, 88.8mm). Monthly mean river flows across SSD ranged from below normal to notably high. End of month groundwater levels ranged from below normal to exceptionally high. Soils across SSD ended the month wetter than the average for December. End of month reservoir stocks were above average at Ardingly Reservoir (Ouse) and below average at Arlington Reservoir (Cuckmere).
2. Rainfall
SSD had below average rainfall in December, receiving 66% (59mm) of the LTA (88.8mm). The areal units in Hampshire received lower rainfall, than most of the those in Sussex. The Lymington areal unit received the lowest rainfall with 52% (48mm) of LTA (91.8mm). The Cuckmere and Ouse areal units in the east of SSD received the highest rainfall with 82% (70mm and 71mm, respectively) of LTA.
Between 2 and 5 December about 50% of the month’s rainfall fell. The highest rainfall totals fell on the 4 December when 29mm was recorded at Plumpton (East Sussex Chalk) and 26mm at Duncton (Western Rother Greensand). Both Chilgrove House (West Sussex Chalk) and Carisbrooke RGs (Isle of Wight) also received about 21mm of rain on 4 December.
However, the last 12 months (January to December) has been the eighth wettest on record for SSD (since 1871). The Test Chalk and East Sussex Chalk areal unit recorded their third wettest calendar year and the Ouse and Cuckmere units their fifth wettest. All the SSD areal units recorded rainfall in the top 10 wettest on record.
Over the longer time periods, the 14-month, 18-month and 24 month running totals remain exceptionally high and were the wettest on record for SSD.
3. Soil moisture deficit and recharge
Soils across SSD ended the month wetter (0mm) than the average for December (7mm).
4. River flows
Monthly mean river flows across SSD ranged from below normal to notably high.
Flows were below normal on the River Wallington at North Fareham.
Flows were normal on the:
- River Meon at Mislingford
- River Arun at Alfoldean
- River Ouse at Goldbridge
- River Cuckmere at Cowbeech
- River Lymington at Brockenhurst
- River Medina at Blackwater
- River Rother at Iping Mill
- River Adur at Sakeham
Flows were notably high on the:
- River Test at Chilbolton
- River Test at Broadlands
- River Itchen at Allbrook and Highbridge
The monthly mean flows for December for the River Test were the fifth highest on record at Chilbolton (1989), and the sixth highest at Broadlands (1958). Monthly mean flows were the seventh highest on the River Itchen at Allbrook & Highbridge (1959).
5. Groundwater levels
End of month groundwater levels for December ranged from below normal to exceptionally high.
Groundwater levels were below normal at Carisbrooke Castle (Isle of Wight).
Groundwater levels were normal at:
- Catherington (East Hampshire Chalk)
- Harting Common (Western Rother Greensand)
- Chilgrove (West Sussex Chalk)
- Beeding Hill (West Sussex Chalk)
- Houndean Bottom (East Sussex Chalk)
Groundwater levels were above normal at West Meon (East Hampshire Chalk).
Groundwater levels were notably high at:
- Lopcombe Corner (Test Chalk)
- Cornish Farm (East Sussex Chalk)
- Clanville Gate (Test Chalk)
Groundwater levels were exceptionally high at:
- Preston Candover (East Hampshire Chalk)
- Youngwoods Copse (Isle of Wight)
The exceptionally high groundwater levels for December were the second highest on record at Youngwoods Copse (1978), and fourth highest at Preston Candover (1975). The notably high levels for December were the fifth highest at Clanville Gate (1966) and Lopcombe Corner (1963). Conversely, the end of month groundwater level at Carisbrooke Castle (Isle of Wight represents the tenth lowest level for December on its record (1977).
6. Reservoir stocks
End of month reservoir stocks were above average at Ardingly Reservoir (Ouse) and below average at Arlington Reservoir (Cuckmere). Ardingly Reservoir (Ouse) was at 99.8% of total capacity (LTA 87%) and Arlington Reservoir (Cuckmere) was at 65% of total capacity (LTA 87%).
7. Environmental impact
During December only one licence restriction was in force on the River Meon and this was lifted by the end of the month.
No flood warnings were issued for SSD in December, but 4 fluvial flood alerts and 1 groundwater alert were issued. All the fluvial alerts were located in Sussex. The groundwater alert was issued in Hampshire for headwater catchments of the River Itchen.
Author: HydrologySSD@environment-agency.gov.uk
Contact Details: 03708 506506
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.