River flows across the majority of the UK are likely to be normal to below normal in January and over the first three months of the year. This signal is particularly strong in most of southern and eastern England, where below normal flows are more likely than those in the normal range for both timeframes. The groundwater outlook for the Chalk of southern England for both January and January-March is for below normal levels. In January, for other aquifers and regions of the UK the outlook shows substantial regional variability. The three-month outlook is for above normal groundwater levels in southern Scotland and normal to below normal levels further south.
With the exception of the Scottish Highlands, all regions of the UK registered below average rainfall in December. Rainfall deficiencies were particularly extreme in England and Wales, most of which received less than half of the average, with less than a third of average for the counties of southern England.
The rainfall outlook for January and for January-February-March (released by the Met Office on 15th December 2016) suggests that there is only a slight shift from the normal range of expected conditions, with above-average and below-average precipitation considered nearly equally probable. The probability that UK-average precipitation for January-February-March will fall into the driest of five equal categories is between 15 and 20% and the probability that it will fall into the wettest of five equal categories is between 15 and 20% (the 1981-2010 probability for each of these categories is 20%).
December river flows were substantially below average for the majority of the country, notably so in Northern Ireland and south Wales, and exceptionally so in southern England and parts of the Midlands. Many rivers in southern England recorded less than a third of average flows for the time of year and were the lowest December mean flows on record.
The outlook for January is for a continuation of below normal flows across the majority of southern and eastern England. For some catchments in East Anglia and the far south-east of England, there is an increased likelihood of notably low flows. Normal to below normal flows are likely for most of the rest of the UK, though the signal for continued below normal flows in the generally wetter and more responsive northern and western areas is less strong. The outlook over the first three months of the year is very similar to that for January, with below normal flows most likely in the south-east and normal to below normal flows elsewhere. There is also the suggestion that average flows over the next six months in parts of East Anglia and the far south of England may be below normal and in some cases notably low.
Whilst groundwater levels in the Permo-Triassic sandstones of the Midlands were above normal, levels in the majority of boreholes in southern parts of England and Wales were below normal, notably so along the south coast. Below average rainfall for most of England and Wales through the autumn and early winter has prevented substantial groundwater recharge.
Below normal groundwater levels in the southern Chalk are likely to continue in January, with notably low levels in some localised areas; levels are unlikely to be above normal even under extremely high rainfall scenarios. In the Carboniferous Limestone of the Midlands the January outlook is also for below normal levels, though this signal is not as strong as that for the southern Chalk. The three-month outlook for the southern Chalk is similar to that for January, although there is slightly less confidence that below normal levels will characterise such wide areas of the aquifer. Over the three-month timeframe, above normal groundwater levels are likely for southern Scotland with normal to below normal levels elsewhere.