October 2014


Period: From October 2014      Issued on 10.10.2014 using data to the end of September

Summary

After a very wet August, the UK registered its driest September on record.  The low rainfall caused river flows and groundwater levels to decline throughout September,  and at the beginning of October soil moisture deficits were above normal for the time of year.  The one month outlook for October is for both river flows and groundwater levels to be within the normal range, with some localised exceptions.  The three month outlook is suggestive of a similar pattern, with normal conditions most likely for the next few months.

Rainfall

The latest predictions for UK precipitation favour near- or above-average rainfall during October and above-average rainfall for October-November-December as a whole.  The probability that UK precipitation for October-November-December will fall into the driest of five equal categories is around 15% and the probability that it will fall into the wettest category is between 25 and 30% (the 1981-2010 probability for each of these categories is 20%).

 

River flows

September river flows were generally below normal across the north and west of the UK, exceptionally so in north Wales and parts of Scotland.  Flows remained in the normal range or above in south-east England and north-east Scotland, a reflection of intense rainfall in winter 2013/14 and in August 2014, respectively.  The one month outlook suggests that normal flows are the most likely outcome throughout the UK.  The influence of the wet winter of 2013/14 in south-east England has finally declined in importance, with some local exceptions in the Thames catchment.  Over the next three months, the dominant signal is for normal conditions for the majority of the UK, although the outcome for specific locations is contingent on the location of rainfall received over the remainder of 2014.  In general for most of the UK, below normal flows are more likely than above normal flows, but normal flows are the most likely outcome over both the one- and three-month timeframes for most of the UK.

Groundwater

September groundwater levels continued to fall back into the normal range, and there were few examples of groundwater recharge commencing.  Levels in the Permo-Triassic sandstones of south-west England remained exceptionally high in response to winter 2013/14.  Levels in the Chalk varied spatially according to aquifer properties, whilst some responsive boreholes in the west of the UK registered notably low levels.  The one month outlook is for levels to be within the normal range, with some localised above normal or below normal levels in response to aquifer characteristics.  The three month outlook is suggestive of a similar pattern, but there is a wider range of possible outcomes owing to the sensitivity of groundwater levels to rainfall over the remainder of 2014 and its impact on the commencement of the recharge season.