November: Generally settled weather with one stormy interlude

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November was a cold, generally settled month and, with the exception of one stormy interlude, frequently under the influence of high pressure. 

The majority of substantial rainfall occurred within an unsettled three‑day period mid-month, outside of which notable rainfalls were relatively uncommon. 

Notably high river flows were registered during this short stormy interlude, particularly in south-west England and the Scottish Borders, resulting in fluvial flooding and substantial disruption to transport networks. Despite this, average river flows for November were markedly below average across most of Northern Ireland and western Britain and generally within the normal range elsewhere. 

Whilst the water resources situation remains favourable overall, below average reservoir stocks in certain areas of the UK and the continued delay in aquifer recharge necessitate vigilance, particularly in light of seasonal outlooks which suggest drier weather is more likely than wetter weather for at least the early part of winter.

November 2016 was a sharp contrast to the conditions of November 2015 which preceded one of the wettest periods on record as documented in our new report on the Winter Floods of 2015/2016 which was published last week.

The assessment is contained in the latest monthly hydrological summary for the UK, the most authoritative analysis of water resources status in the country. The monthly summaries are produced by the National Hydrological Monitoring Programme, operated by the Centre for Ecology & Hydrology in conjunction with the British Geological Survey.

On the 19th/20th November, the first named storm of the season, ‘Angus’, tracked across the south of England, bringing destructive winds (causing power cuts for 2,200 properties), intense rainfall (e.g. 27mm in one hour at Exeter Airport) and surface water flooding. A more disruptive low pressure system followed shortly thereafter on the 21st/22nd, slowly traversing north-eastwards across England. Persistent heavy rainfall (e.g. 70mm at Chillingham Barns, Northumberland) onto ground saturated by rainfall from ‘Angus’ caused substantial disruption to road and rail travel (including the South West and East Coast main lines).

River flows

Between the 19th and 21st , river flows across England increased markedly in response to persistent heavy rainfall; flows on the Tone increased from new early November minima to register one of the highest flows in a 56‑year record. Daily flows approached or exceeded previous November maxima for the Whiteadder Water, Exe, Brue and Otter; for these last three, flows ranked amongst the highest registered in any month (each in records of at least 50 years). 

In the south‑west, properties in Braunton and Bradiford were flooded and the Mole overtopped forcing the evacuation of a caravan park. During the second storm, more than 40 Flood Warnings and 140 Flood Alerts were issued and fluvial flooding was reported in locations including Bristol, Greater Manchester and Rotherham. 

Over the final week of the month, high pressure led to protracted recessions on most rivers. 

For the autumn overall, notably low flows characterised an extensive area of western Scotland (the Naver was exceptionally low), Northern Ireland and north Wales, with below normal flows throughout western parts of the UK. River flow deficiencies for much of western Britain have now extended over six months; the Annacloy registered a third of average flow over this timeframe.

Monthly rainfall and weather

The unsettled period mid-month was sufficient for England to register above average rainfall. For the rest of the UK, rainfall was notably below average under predominantly anticyclonic conditions, the culmination of a dry autumn for much of the country. 

Groundwater and reservoir levels

Groundwater levels generally continued their seasonal recession in early November although some boreholes responded rapidly to heavy rainfall mid-month. 

Although reservoir stocks for England & Wales were near average for November, some individual impoundments were substantially below average; stocks for Ardingly and Wimbleball were more than 20% below average, and Clatworthy similarly despite doubling its stocks during November. In Northern Ireland and parts of western Scotland, stocks fell relative to average and were around 15% below average. 

Additional information

A PDF of the full 12-page November 2016 summary can be downloaded here.

The monthly summary is a look back at hydrological events occurring in November 2016. Latest information on flood warnings is provided by the Environment Agency, Natural Resources Wales and Scottish Environment Protection Agency (flood warnings for Northern Ireland are not available).

The Centre for Ecology & Hydrology jointly operates the National Hydrological Monitoring Programme (for the UK) in conjunction with the British Geological Survey. NHMP scientists produce the UK Monthly Hydrological Summary which assesses rainfall, river flows, groundwater and reservoir levels. They also operate the UK’s National River Flow archive.

The NHMP also has a remit to analyse major flood and drought events in the UK and analyse long-term trends in UK hydrological data. The UK Monthly Hydrological Summary is normally published on, or before, the tenth working day, of the following month. A Hydrological Outlook for the UK is also available, and is updated monthly. The latest Outlook can be viewed here.

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