Research and analysis

Wessex water situation: May 2024 summary

Updated 21 June 2024

Applies to England

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

1. Summary

May showed a small increase in rainfall compared to April. An average of 98mm of rain fell across Wessex, 160% of the long term average (LTA). While not record breaking rainfall in May alone, the last 6 months (December to May) has been the second wettest since records began in 1871 and the last 12 months (June to May) has been the wettest on record. Soil moisture deficit (SMD) largely remained close to 0mm across the month. Monthly mean river flows were normal and above normal across much of the north of Wessex but notably high and exceptionally high in the south of Wessex. Groundwater monitoring sites monitoring the Chalk recorded between normal and exceptionally high levels while those monitoring other formations recorded exceptionally high levels. Throughout May, reservoir levels for Wessex Water remained close to 100% capacity while Bristol Water reservoir levels were steady at approximately 94% capacity.

2. Rainfall

An average of 98mm of rain fell across Wessex in May (160% of the LTA), making it the 10th month in the last 12 to have rainfall above the LTA. May was predominantly dry at the start of the month except for heavy rainfall on 1 May (18% of the monthly total rain) and 13 May (23% of the monthly total rain). A total of 77% LTA rainfall for the whole month fell at Marshwood Lodgehouse rain gauge in Dorset on 13 May alone. May 2024 ended with a wetter period between 25 and 29 May when 28% of the total rainfall for the month fell.

In May most hydrological areas recorded either above normal or notably high amounts of rainfall. Most hydrological areas in the north of Wessex recorded above normal levels while most in the south of Wessex recorded notably high levels. The exceptions were West Somerset Streams which received normal rainfall levels and West Dorset Streams and the River Frome which both received exceptionally high levels. Over the longer term, the majority of hydrological areas recorded exceptionally high rainfall over the past 3 months with exceptions in the north and west of Wessex which recorded notably high levels. Over the past 6 and 12 month period, all hydrological areas recorded exceptionally high rainfall. As a result, this has been the fourth wettest 3 months (March to May), second wettest 6 months (December to May) and wettest 12 months (June to May) since records began in 1871.

3. Soil moisture

SMD remained close to 0mm across most of Wessex during May, although small areas to the east of Wessex recorded in the range of 11mm to 40mm. This is notably lower than SMD this time last year. The majority of Wessex recorded a SMD of 26% to 50% lower than the LTA, with a couple of areas to the west and east of Wessex recording a SMD between 6% to 25% lower than the LTA.

4. River flows

Sites in the north of Wessex mainly recorded normal and above normal monthly mean flows in May 2024. Sites in the south of Wessex, including those in Chalk catchments all recorded notably high and exceptionally high monthly mean flows. All sites recorded reduced flows at the end of May in comparison to the end of April. At the end of the month most daily mean flows were starting to decrease following the wet period towards the end of the month.

5. Groundwater levels 

Groundwater sites across Wessex recorded between exceptionally high and normal levels at the end of May. Amongst sites monitoring the Chalk, 2 reported above normal levels and 2 reported notably high levels. Oakley Industrial Estate (monitoring the Chalk) reported normal levels while Kingston Russell Road was the only site monitoring the Chalk to report exceptionally high levels. The 3 remaining sites, Didmarton (monitoring the Inferior Oolite formation), Allington (monitoring the Great Oolite formation) and Overcompton (monitoring the Bridport Sand formation) all recorded exceptionally high levels.

6. Reservoir stocks

Reservoir levels in Wessex remained close to 100% capacity during May for Wessex Water, reporting at approximately 98% full which is similar to the levels recorded this time last year. Bristol Water reported approximately 94% storage capacity which has remained steady throughout the month. This is similar to levels reported at the end of May last year.

Author: Wessex Hydrology, hydrologywessex@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.