Research and analysis

Water situation : September 2024 summary

Updated 12 December 2024

Applies to England

It has been a very wet month across England with most catchments receiving above average rainfall during September. Soil moisture deficits (SMD) have decreased across England, with soils in many parts of the country ending September considerably wetter. River flows increased at all but 4 of our indicator sites in September and were classed as normal or higher at all sites. Groundwater levels decreased at nearly three-quarters of the sites we report on and levels at more than half of sites remain classed as notably or exceptionally high for the time of year. Reservoir storage decreased at more than three-quarters of the reservoirs we report on and the majority of reservoirs were classed as normal or higher. Reservoir stocks across England were 76% full at the end of September.  

1. Rainfall

The rainfall total for England for September was 133mm which represents 189% of the 1961 to 1990 long term average (LTA) for the month (195% of the 1991 to 2020 LTA). Most hydrological areas received above average rainfall during September with only 9 catchments receiving below average rainfall. The wettest hydrological area relative to the LTA was the Cotswold East catchment in south-east England which received 394% of LTA rainfall. The driest hydrological areas was the Derwent catchment in north-west England which received 61% of LTA rainfall in September. (Figure 2.1)

September rainfall totals were classed as normal or higher for the time of year in all but one catchment in England. Seventy-eight catchments (56%) were classed as exceptionally high for the time of year. Thirty-one hydrological areas recorded the wettest September since 1871. Additionally it was also the wettest September for central England since 1871. At the regional scale, September rainfall totals were a mixed picture. In south-east and central England rainfall was classed as exceptionally high whereas in north-west England rainfall was classed as normal. Rainfall in south-west and east England was classed as notably high and the north-east was above normal. For England as a whole rainfall was classed as exceptionally high. (Figure 2.2)

The 3-month cumulative totals were classed as normal or higher in all catchments with more than two-thirds of the catchments classed as above normal or higher. Three hydrological areas in south-east England, Cotswolds East, Cotswold West and Thame, all recorded their wettest 3 months (July to September) since 1871. The 6 month cumulative totals show a similar picture with rainfall classed as normal or higher in all catchments with all but 16 catchments classed as above normal or higher. The 12 month cumulative totals were exceptionally high in all but 4 catchments and it has been the wettest 12 months (October to September) since 1871 for 67 catchments. It has also been the wettest 12 month period ending in September for central and south-west England. Furthermore, England as a whole recorded the wettest 12 month period ending in September since 1871. (Figure 2.3)

2. Soil moisture deficit

Due to above average rainfall soil moisture deficits decreased significantly across most of England particularly across central, eastern and southern England. (Figure 3.1)

At a regional scale, soils across all areas of England remain wetter than average for the time of year. Across all regions of England soil moisture deficits had decreased sharply by the end of September and soils in north-west, south-west and central England had close to no SMD. (Figure 3.2)

3. River flows

Monthly mean river flows increased at all but four indicator sites in September. September monthly mean flows remain classed as normal or higher at all sites. Nineteen sites (35% of the total) were classed as exceptionally high for the time of year. Fourteen sites (25% of the total) were classed as normal for the time of year and 13 sites (24%) were classed as above normal. Nine sites (16%) were notably high. Seven sites recorded their highest monthly mean flow for September on record (record start given in brackets) in the:

• north-west, the River Weaver (since 1977)
• east England, the Bedford Ouse (since 1972) and the Nene (since 1970)
• south-east, the River Itchin (since 1958), the River Ouse (since 1979) and the River Ver (since 1956)
• south-west, the Upper Avon (since 1965) (Figure 4.1)

Monthly mean flows for September increased at all but one of the regional index sites. Flows at Caton on the River Lune in north-west England decreased however they remain classed in the normal range. Flows in The River Exe in south-west England were also classed as normal.  Naturalised flows at Kingston on the River Thames and flows at Orford on the Bedford Ouse in east England increased and were classed as exceptionally high for the time of year. The River Dove in central England and the South Tyne in the north-east both recorded above normal monthly mean flows. The Great Stour in south-east England recorded notably high flows for September. (Figure 4.2)

4. Groundwater levels   

At the end of September, nearly three-quarters of the groundwater indicator sites we report on recorded a decrease in levels. Levels at all indicator sites were normal or above for the time of year with more than a third of groundwater levels classed as exceptionally high. Seven sites were classed as normal at the end of September. Four sites recorded their highest end of September groundwater level on record including:

• Weir Farm (since 1983) in Bridgnorth Sandstone in central England
• Coxmoor (since 1990) in Idle Torne Sandstone in central England
• Priors Heyes (since 1972) in West Cheshire Sandstone in the north-west
• Skirwith (since 1978) in Carlisle Basin Sandstone in the north-west (Figure 5.1)

Groundwater levels decreased at all aquifer index sites in September with the exception of Jackaments Bottom (Burford Jurassic Limestone) in the south-east where levels increased to be classed exceptionally high. Levels at Weir Farm (Bridgnorth Sandstone), Skirwith (Carlisle Basin Sandstone) and Stonor Park (South West Chilterns Chalk) remain classed as exceptionally high for the time of year. Levels at Little Bucket (East Kent Stour Chalk) and Redlands Hall (Cam and Ely Ouse Chalk) were notably high and above normal respectively. Chilgrove (Chichester Chalk) and Dalton Estate (Hull and East Riding Chalk) were classed as normal for the end of September. (Figure 5.2)

5. Reservoir storage

Reservoir storage decreased during September at over three-quarters of the reservoirs and reservoir groups we report on. The largest stock decrease was at Farmoor in south-east England which decreased by 10%. Most reservoirs and reservoir groups we report on at the end of September were classed as normal or higher for the time of year. Four reservoirs were classed as below normal and one, the Pennines Group in north-west England, was classed as notably low. The Dee system continues to be impacted by ongoing reservoir maintenance and was classed as below normal. (Figure 6.1)

At a regional scale, total reservoir storage decreased in all regions. In south-west England, overall storage decreased by 5% during September. For England as whole, storage decreased to 76% at the end of September. (Figure 6.2) 

6. Forward look

October had an unsettled start, with wet conditions in many places, particularly the south-west of England. Through the middle of October, conditions are expected to settle with longer, drier spells in the south and east and the greatest chance of rain in the north. Some wet and windy conditions may set in to the north-west towards the end of the month, but more settled conditions are likely as high pressure becomes dominant. This could bring frost and fog at night, as the difference between daytime and overnight temperatures becomes large.

For the 3 month period for the UK from October to December, precipitation is expected to be near average, with normal chance of either dry or wet conditions. There is a greater than normal chance of conditions being mild, however cold spells remain possible particularly late in the period.

6.1 Projections for river flows at key sites

By the end of March 2025, river flows are projected to have a greater than average chance of being above normal or higher in east, central, south-west and south-east England. In north-east England, river flows have the greatest chance of being normal or lower for the time of year.

By the end of September 2025, river flows are projected to have a greater than average chance of being above normal or higher in south-east, south-west and central England. In north-west and east England, river flows have the greatest chance of being normal or higher, while in north-east England, river flows have the greatest chance of being below normal or lower.

6.2 Projections for groundwater levels in key aquifers

By the end of March 2025, river flows are projected to have a greater than average chance of being above normal or higher in east, central, south-west and south-east England. In north-east England, river flows have the greatest chance of being normal or lower for the time of year.

By the end of September 2025, river flows are projected to have a greater than average chance of being above normal or higher in south-east, south-west and central England. In north-west and east England, river flows have the greatest chance of being normal or higher, while in north-east England, river flows have the greatest chance of being below normal or lower.

Author: National Water Resources Hydrology Team, [email protected]

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.