Research and analysis

Devon and Cornwall water situation: December 2024 summary

Updated 14 January 2025

Applies to England

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

1. Summary

Devon and Cornwall received 60% of the December long term average (LTA) rainfall, which was below normal for the time of year. Soil moisture deficit (SMD) increased initially in December before decreasing again in the second half of the month, ending the month similar to the LTA for the time of year. Monthly mean river flows ranged from below normal to normal for the time of year across the area. Groundwater levels ended the month between below normal and exceptionally high for the time of year. Total reservoir storage across Devon and Cornwall ended the month at 89% net storage, with Wimbleball, Colliford and Roadford reservoirs at 87%, 79%, and 95% of net storage respectively at the end of December.

2. Rainfall

Devon and Cornwall received 83mm of rain during December (60% of the December LTA), which is classed as below normal for the time of year. Rain fell throughout the month, but the most significant periods of rain occurred between 4 and 6 December and between 17 and 23 December, as well as on the first and last day of the month. December was one of 4 months in the last 12 months to have experienced below average rainfall.

In December, rainfall was below normal in most hydrological areas except for the Otter, Sid, Axe and Lim, Fal and St Austell, and West Cornwall hydrological areas, where rainfall was notably low for the time of year. Cumulative rainfall in the last 3 and 6 months has been normal for the time of year across most areas. In the last 12 months, most of Cornwall and north Devon recorded notably high cumulative rainfall, with most of south Devon and east Devon recording exceptionally high cumulative rainfall.

3. Soil moisture deficit

SMD increased in the first part of December, before decreasing again in the second half of the month. The average deficit for Devon and Cornwall remained below 10mm for the whole of December, meaning the average deficit was similar to the LTA for the time of year. The SMD at the end of December was similar to the SMD at the end of December 2023.

SMD was less than 10mm across the whole Devon and Cornwall area on 1 January, which is within 5mm of the LTA.

4. River flows

December monthly mean river flows ranged between below normal to normal for the time of year. Bellever on the East Dart, Chudleigh Bridge on the Teign, Dotton on the Otter, Gunnislake on the Tamar, Torrington on the Torridge, and Umberleigh on the Taw all recorded below normal monthly mean flows, reflecting lower rainfall in these catchments. Most reporting stations experienced a decrease in daily mean flows over the month with some peaks seen in response to rainfall, particularly from 4 to 6 December. On 31 December, all reporting sites recorded below normal daily mean flows for the time of year, except for Chudleigh Bridge on the Teign and Whitford on the Axe, which reported notably low and normal flows respectively for time of year.

5. Groundwater levels   

On 31 December, groundwater levels were classed as follows:

• exceptionally high at Branscombe Lane (monitoring the Dawlish Sandstone), Whitlands (monitoring the Upper Greensand), Woodbury Common No2 (monitoring the Budleigh Salterton Pebble Beds), and Woodleys No1 (monitoring the Otterton Sandstone Formation)
• normal at Bussels No7A (monitoring the Dawlish Sandstone) and Coleford Production (monitoring the Permian Breccias and Sandstones)
• below normal at Winnards Perch (monitoring the Staddon Formation)

6. Reservoir stocks

Total reservoir storage was 89% at the end of December, which is an increase of 3% in storage since the end of November. This is higher than the total storage at the same time last year and in 2022. At the end of the month, storage at Wimbleball, Colliford and Roadford was 87%, 79% and 95% of net storage respectively, compared to 100%, 73% and 82% this time last year.

Author: Devon and Cornwall Hydrology, hydrology.dandc@environment-agency.gov.uk

All data are provisional and maybe subject to revision. The views expressed in this document are not necessarily the views of the Environment Agency. Its officers, servants, or agents accept no liability for loss or damage arising from the interpretation or use of the information, or reliance upon views contained in this report.