December 2014


Period: From December 2014      Issued on 10.12.2014 using data to the end of November

Summary

Although November rainfall for the UK overall was near-average, there were notable regional variations.  Southern and eastern areas of the country were much wetter than average, causing above normal river flows and groundwater levels in responsive catchments and boreholes.  Below average rainfall in northern and western parts of the UK caused below normal river flows within these areas.  The one month outlook for December is for both river flows and groundwater levels to be within the normal range for most of the UK apart from lowland England, where river flows are likely to be above normal.  The three month outlook suggests a similar pattern, but with an increased likelihood of above normal groundwater levels in the Permo-Triassic sandstones of north-west England. 

Rainfall

Latest predictions for UK-mean precipitation favour near-to or above-average rainfall for December and for the December-January-February period as a whole.  The probability that UK precipitation for December-January-February will fall into the driest of five equal categories is between 10% and 15% and the probability that it will fall into the wettest category is around 25% (the 1981-2010 probability for each of these categories is 20%).

River flows

November river flows were above normal for many catchments in eastern Scotland and southern, central and eastern England, closely corresponding with those areas which experienced above average rainfall.  Similarly, below normal flows were registered in northern and western parts of England, Scotland and Wales in response to below average rainfall in November.  The one month outlook suggests that river flows in all regions apart from lowland England will fall within the normal range in December.  The most likely outcome for many catchments in lowland England is for river flows to be above normal.  For the three month outlook, the situation is broadly similar.  River flows within the normal range are most likely for the majority of the UK, but there is a higher likelihood of above normal flows in parts of lowland England.

Groundwater

Groundwater recharge commenced in November, and groundwater levels were normal to above normal throughout the UK.  Levels in the Chalk were in the normal range or higher, with above normal levels recorded in more responsive Chalk boreholes.  Levels in the Permo-Triassic sandstones of western England and Wales continued to be above normal, exceptionally so for some boreholes in the south-west and the Midlands.  The one month outlook is for normal to above normal levels, with some localised exceptions below normal in December.  Despite some uncertainty, over the three month timeframe it is unlikely that groundwater levels will be below normal except for the most extreme dry rainfall scenarios.  Similarly, levels in the Permo-Triassic sandstones of north-west England are likely to be above normal for winter 2014/15.