September 2014


Period: From September 2014      Issued on 15.09.2014 using data to the end of August

Summary

In contrast with the dry early summer, August was wet across much of the UK, which has had an influence on the September outlook. The wet August reversed the decreasing soil moisture trend of the last few months, although this may prove to be temporary as early September has been dry. The one month outlook is for river flows to be normal to above-normal in northern Scotland and much of southern and eastern England, with normal flows elsewhere. Groundwater levels are likely to be in the normal range or above across all aquifers.  Projections for the next three months are for river flows and groundwater levels to be in the normal range or above across much of the UK, suggesting that the water resources situation will be favourable entering the winter. Autumn is  typically the time of year when groundwater recharge commences, so the long-term outlook is very contingent on rainfall over the next three months.

Rainfall

The latest predictions for UK precipitation slightly favour below-average rainfall for both September and  September-October-November as a whole. The probability that UK precipitation for September-October-November will fall into the driest of five equal categories is around 30% and the probability that it will fall into the wettest category is 25% (the 1981-2010 probability for each of these categories is 20%).

 

River flows

August river flows were exceptionally high in northern Scotland (with flooding in many Highland catchments) and above-normal in the southeast and parts of eastern England, but mostly normal elsewhere. The one month outlook is for a continuation of these broad patterns: flows are likely to be normal to above normal in southeast England and northern Scotland (with an increased likelihood of notable or exceptional flows in the latter), with normal flows the most likely outcome elsewhere. Over the next three months, there is significant uncertainty in the outlook, with a wide range of possible outcomes. Normal flows are generally the most likely outcomes across the UK, although above-normal flows may persist in some catchments in southeast England.

Groundwater

August groundwater levels were normal or above normal levels across all aquifers. Levels were above normal to above normal in the Chalk and Jurassic limestone. Levels in the Magnesian limestone and Permo-Triassic sandstone were above normal, with record levels (for the time of year) persisting in some boreholes in western England. The one-month outlook is for broadly similar patterns to persist. Above-normal levels are likely in parts of the southern Chalk, with normal levels elsewhere in the aquifer. Levels in the Permo-Triassic of northwest England are likely to be above-normal but may decrease from current record high levels. Over the next three months, rainfall will be far more influential in dictating the outlook, so the projections are less certain. The general outlook is for groundwater levels to be normal to above-normal across the majority of aquifers.