1. Summary

January was a return to wetter weather following the dry end to 2024 with an average of 137mm of rainfall across Wessex, 154% of the long term average (LTA). Rain largely fell over a few days at either end of the month. Soil moisture deficit (SMD) remained close to zero during January. In most river catchments on the Chalk, recorded monthly mean flows were above normal and sites in the north of Wessex varied between normal and exceptionally high. Groundwater sites monitoring the Chalk varied between normal and exceptionally high at the end of January while all other monitoring sites reported notably high groundwater levels. Reservoirs ended the month at approximately 99% capacity for both Wessex Water and Bristol Water. For both water companies this was similar to levels in January 2024.

2. Rainfall

In January an average of 137mm (154% LTA) of rain fell across Wessex. Hydrological areas to the south of Wessex received notably high rainfall while areas to the north mostly received between above normal and notably high rainfall. The West Somerset Streams area was the only area to receive normal rainfall. Rainfall during January was largely restricted to 2 periods at either end of the month, 36% of rain fell between 1 and 5 January and 49% between 23 and 27 January during Storm Éowyn and Storm Herminia.

In the last 3 months, most hydrological areas have received normal rainfall on average with 3 areas receiving above normal rainfall. In the last 6 months, most hydrological areas in Wessex received between above normal and notably high rainfall with 2 hydrological areas to the east receiving exceptionally high rainfall and the West Somerset Streams the west receiving normal rainfall. Over the past 12 months almost all areas of Wessex received exceptionally high rainfall.

3. Soil moisture

SMD in Wessex remained close to zero on average throughout January. SMD at the end of the month was near zero on average across all areas of Wessex. SMD at the end of January was within 5mm of the LTA across all hydrological areas of Wessex.

4. River flows

Amongst sites within Chalk catchments, the majority reported above normal mean monthly flows. The exception was Sydling Water at Sydling St Nicholas which recorded normal flows. Amongst sites outside of Chalk catchments, 4 sites towards the centre of Wessex reported exceptionally high monthly mean flows while the remaining sites reported between normal and above normal monthly mean flows in January.

Daily mean flows in January peaked twice during the month after each period of higher rainfall. At the end of January, the majority of reporting sites across Wessex recorded between above normal and exceptionally high daily mean flows.

5. Groundwater levels   

The majority of groundwater monitoring sites across Wessex ended January reporting notably high levels. All 4 exceptions were sites monitoring the Chalk aquifer. Delcombe and Kingston Russell Road to the south of Wessex recorded normal levels at the end of the month while Chitterne Down and Oakley Industrial Estate were both exceptionally high. At the end of January, groundwater levels across all sites apart from Didmarton and Overcompton were increasing.

6. Reservoir stocks

Wessex Water reservoir levels remained close to 100% capacity throughout January. Overall, Bristol Water reservoir levels increased slightly, having begun the month at approximately 94% capacity and ending January at approximately 99% capacity. The current combined levels for both Wessex Water and Bristol Water are similar to those recorded this time last year and those in January 1995.

Author: Wessex Hydrology, hydrology.wessex@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.