December 2013


Period: From December 2013      Issued on 11.12.2013 using data to the end of November

Summary

The outlook for December is for river flows to be in the normal to below normal range. Groundwater levels are likely to be normal in south-east England, but above normal in the north-west of England. The three month outlook is for this situation to persist. Winter is the critical time of year for groundwater recharge and reservoir replenishment. Whilst the current outlook suggests no immediate concern for water resources, this is dependent on meteorological forecasts which are highly uncertain. These currently suggest a slightly greater likelihood of colder, drier conditions this winter which would naturally increase the likelihood of lower flows and groundwater levels. Much of late-November and early-December has been dry and settled (with the notable exception of the very strong winds that caused major disruption and damage in early December); the persistence of such conditions further into winter could significantly alter the water resource outlook.

Rainfall

Confidence in the forecast for precipitation across the UK over the next three months is relatively low. For the December-January-February period as a whole there is a slight signal for below average precipitation. The probability that UK precipitation for December-January-February will fall into the driest of our five categories is around 25% and the probability that it will fall into the wettest category is around 15% (the 1981-2010 probability for each of these categories is 20%).

River flows

River flows in early November were high in many catchments but declined steadily through what was largely a drier than average month, resulting in monthly flows for November that were in the normal range in a majority of UK catchments. Exceptions were the above normal flows in parts of the south-west, and below normal flows in a number of Scottish catchments. The outlook for December is suggestive of normal to below normal flows in most regions, with below normal flows being more likely in northern and western regions (particularly in north-eastern Scotland) than in the south-east.  A similar pattern of normal to below normal flows extends to the three month forecast. 

Groundwater

The pattern of groundwater levels in December was similar to the previous month, with normal levels across most of the Chalk (with below normal levels in Yorkshire) and Jurassic limestone contrasting with above normal levels in the Permo-Triassic sandstone of the Midlands and north-west England. The one month outlook is suggestive of a continuation of this situation – normal levels are generally favoured across the Chalk, although below normal levels will probably occur in Yorkshire, Lincolnshire and in some boreholes in Wessex, and higher levels will probably persist in north-west England. The three month outlook is suggestive of similar patterns continuing through the winter. Groundwater recharge is at its most effective through the winter period so the long-term outlook is highly contingent on rainfall over the next three months.