October 2013


Period: From October 2013      Issued on 14.10.2013 using data to the end of September

Summary

The general outlook for October is for a continuation of the current situation. River flows are likely to be normal to below-normal, with a high likelihood of low flows in north-east Scotland. Groundwater levels are likely to be normal or above-normal except in the southernmost parts of the Chalk aquifer, where below-normal levels will likely persist. The outlook for the next three months suggests little change to this situation, although considerable uncertainty surrounds any longer-term outlook at this time of year. The late autumn/early winter typically marks the start of the groundwater recharge season, and the timing of its onset will be especially influential on the water resource outlook. Soils are currently very dry for the time of year, which implies a possible delay to recharge, leading to a higher likelihood of below-normal groundwater levels and river flows.   

Rainfall

Confidence in the forecast precipitation over the next three months is low. There is a preference for near-to-below average rainfall during October. For October-November-December as a whole, the signal is similar to climatology, although with a slightly higher probability of above-average rainfall. The probability that UK precipitation for October-November-December will fall into the driest of our five categories is around 20% and the probability that it will fall into our wettest category is 20% (the 1981 – 2010 probability for each of these categories is 20%). 

River Flows

River flows in September were in the normal range or moderately below normal at a majority of sites; below-normal flows were more widespread in north-east Scotland and some catchments in Wales and western England. The one-month ahead outlook suggests the general expectation is for a continuation of the current situation, with normal flows most likely for the majority of the UK but with a higher likelihood of below-normal flows persisting in some areas (in north-east Scotland especially).  The three-month outlook is not suggestive of any major change in this situation, with model projections generally favouring flows in the normal range. However, comparisons with historical data suggests below-normal flows could persist in many catchments. 

Groundwater

Groundwater levels in September were in the normal range across most of south-east England (with the exception of some boreholes in the southern Chalk which were below normal), whilst above-normal levels were registered in many western Permo-Triassic boreholes. The outlook suggests a similar situation for October: normal levels are projected for the majority of boreholes and below-normal levels are likely to persist in parts of the southern Chalk, whilst above-normal levels are likely in some boreholes in the Permo-Triassic. The three-month outlook is suggestive of broadly similar patterns, but these projections are highly uncertain; with notably high soil-moisture deficits in early October, there is a high likelihood of the seasonal onset of recharge being delayed.