Hydrological Outlook from September 2017

Latest Hydrological Outlook from September shows river flows to be normal to above normal across the UK

The one month outlook is for river flows to be normal to above normal across the UK, and a similar situation is most likely over the next three months, except in some localised parts of central southern England where flows may be below normal. The one month and three month outlooks for groundwater suggest a continuation of above normal levels in some northern aquifers, and below normal levels in parts of the Chalk of south-east England, suggesting the recharge season will commence from a below normal baseline in some areas.


Rainfall during August was very variable, spatially, but much of the country saw above average rainfall (the UK rainfall was 120% of average ) and it was particularly wet in Scotland and south-east England.

The Met Office 3-month Outlook issued on 24th August indicated that for September the chances of above- and below-average precipitation are fairly balanced.  For September-October-November as a whole, above-average precipitation is considered slightly more probable than below-average precipitation.

The probability that UK precipitation for September-October-November will fall into the driest of five equal categories is 20% and the probability that it will fall into the wettest of these categories is around 25% (the 1981-2010 probability for each of these categories is 20%). 

River flows

August river flows were mostly in the normal range or above normal, with above normal flows particularly prevalent in northern and western Britain and a more mixed pattern in lowland England. Below normal flows were observed in some catchments in central southern England.

The one month outlook is for normal flows to predominate across most of the country. However, there is a slight signal for above normal flows in most regions, reflecting the wet August, particularly in central and eastern Scotland; a wet start to September increases the likelihood of flows being above the normal range. The three month outlook suggests normal to above normal flows in all regions of the UK. In some groundwater-fed catchments in central southern England where flows are currently low, below normal flows may persist over the next three months.


Across much of the Chalk aquifer, August groundwater levels were below normal or notably low, although recovery was evident in some boreholes. In other aquifers, levels were normal or below normal except in some northern boreholes where levels were above normal or exceptionally high.

The one month outlook is for a broadly similar situation to persist. The three month outlook is also similar, although levels in the western Chalk may return to the normal range. Below normal levels are likely to persist through autumn in the Chilterns, parts of east Anglia and the North Downs. Above normal levels are likely in some northern aquifers. However, over this period, autumn rainfall will become influential in determining the long-term groundwater outlook.

Additional information

You can access the full summary here.

The Hydrological Outlook is produced in a collaboration led by the Natural Environment Research Council’s Centre for Ecology & Hydrology (CEH) and involving the Natural Environment Research Council’s British Geological Survey (BGS), the Environment Agency (EA), the Met Office (MO), the Scottish Environment Protection Agency (SEPA), Natural Resources Wales (NRW), and the Rivers Agency Northern Ireland (RA).

Data are provided for the Hydrological Outlook by the EA, NRW, SEPA and RA.

Meteorological data and modelling expertise are provided by the MO.

Hydrological and hydrogeological modelling expertise are provided by CEH, BGS and the EA.