Long-term rainfall and runoff deficiencies were extended during a dry January in parts of the UK, though it was also a month of contrasts. At the national scale, it was the driest January since 2006, with the UK receiving 63% of the long-term average. Moderately above average rainfall was received in south-east England, but large areas of northern Britain registered less than half the typical January total, with some substantially drier pockets. Rainfall across aquifer areas in the English Lowlands triggered localised increases in groundwater levels, but levels remain well below the normal range across the Chalk.
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.
There were few deep depressions and notable daily rainfall totals and fluvial flood alerts were rare by the standards of recent winters. Modest, but welcome, replenishment was seen in many reservoirs, but at the national scale stocks remained substantially below average (for England & Wales as a whole, stocks were the lowest for January since 1997). Stocks were 30% below average or lower in some impoundments (Wimbleball and Ardingly in southern England, and Silent Valley in Northern Ireland).
The October-January rainfall for the UK was 65% of average, the second lowest average for these months on record (from 1910), with exceptional deficiencies in some northern and western areas – it was the driest on record for this timeframe for Northern Ireland. In southern Britain the recent anomalies are less exceptional, but more significant deficiencies are apparent from the summer: south-west England saw its second lowest July-January rainfall in a series from 1910.
Summary author Jamie Hannaford said, "In most areas, water resources are generally resilient to a single dry winter, but the observed deficiencies increase the potential for pressures later in the year. With the window for substantial aquifer and reservoir replenishment narrowing before evapotranspiration rates begin to climb, late-winter/early-spring rainfall patterns will have a significant bearing on the long-term water resources outlook."
He added, "February started wet, but the latest outlooks suggest a drier end to winter and no clear signal for the spring."
The monthly summary is a look back at hydrological events occurring in January 2017. 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.